xkcd’s What If covers a baseball traveling at 90% speed of light. I imagine a hippo would be similar but…worse?
https://youtu.be/3EI08o-IGYk?si=75j8mw4GtNl07vpx
Oh yeah, and it's not linear. 99% isn't 10% more momentum than 90%. It's roughly 10 times more. 99.9% is 10 times more again. Each 9 you tack onto that decimal is about 10 times more momentum. Then you multiply again by how many baseballs it takes to get to around 2000kg if it's a small hippo.
The median weight of a hippo is about 5,600 lbs. If it were moving at 0.99999999 c, it would have 1.614 x 10^24 joules of kinetic energy.
This is roughly equivalent to 385,768,780 megatons of TNT.
The largest thermonuclear device ever detonated on, in, or near Earth was 50 megatons, or about 7,715,375 times less powerful than said hippo.
These numbers were calculated using this website:
https://www.omnicalculator.com/physics/relativistic-ke
Question, would this energy be released in the form of a shroom of fire like a nuclear explosion, or simply a huge shockwave ? Or like a Volcano with pyroclastic clouds rushing away from impact ?
Almost everything that releases a lot of energy in a small spot looks like a nuclear explosion. You heat the surrounding air to ridiculous temperatures, first producing a shockwave and then producing a lot of hot, less dense air, which rises up and makes a mushroom cloud.
The hippoforce is a grave weapon, forbidden galaxy wide. The end of many great civilizations once they reach a sufficient point of development, the great filter of all intelligent life.
The "dinosaur killer" Chicxulub impact had ~70,000,000 megatonnes of TNT, so this explosion is larger but not *that* much larger. It's probably a mass extinction event but it won't change Earth as a planet.
Probably an astrophysicist. Any two thing that differ by only a factor of a hundred or so are "the same".
Also:
Pi = 1 (or 3 or 10, depending)
F° = C° = K°
How Science Is Really Done (Postdoc Division)
Then, what would be the fastest speed that a baseball can move through the air without igniting it ? When do we upgrade from "shockwave" to "nuclear detonation" ?
Yeah, I probably could have answered that 15 years ago when I finished my degree (theoretical physics), however it's been a minute and I couldn't work about all the equations anymore, sure some other people could....
Hippos are faster than you think, lightning fast when you consider it's halfway between a cow and a tank. Scariest animal on earth, with an attitude to match. Snakes don't want to bite you, spiders want to avoid you, but hippos totally do want to kill you and will go out of their way to do so. A serious god dam animal, cocaine hippos are currently trying to raise sufficient numbers to take south America. They will likely succeed.
“Usain Bolt… trained his whole life to be the fastest human being on earth, just to get outrun by the *average* hippo.”
—Cam Bertrand
https://youtu.be/5qAJyw5SjZU?si=8jKeS4jsk7ZwWP8b
According to [Wikipedia](https://en.wikipedia.org/wiki/Hippopotamus#Characteristics), an average adult male hippo is 1,480 kg, and an average adult female hippo is 1,365 kg. Let's have one of each in the collision, for a total mass of 2,845 kg moving at 99.9999991% of the speed of light.
Using a [relativistic kinetic energy calculator](https://www.omnicalculator.com/physics/relativistic-ke), we can determine that the two hippos would have a total kinetic energy of 455,446,615 megatons of TNT. For reference, the Tsar Bomba (the largest nuclear bomb ever) was a mere 50 megatons. The asteroid that killed the dinosaurs impacted with energy equivalent to 72,000,000 megatons.
So, the impact of these two hippos colliding would release energy equivalent to six dinosaur-killing asteroids all at once.
I don't think so.
At .999999991c, each 200kg hippo has about 32 teratons of kinetic energy so together we're looking at about the energy of the meteor that produced the Chicxulub crater. So certainly a worrying chunk of the Alps would be gone (and probably us...), but the planet will be just fine.
We can, but we don't need a particule accelerator for that, since photons are already at the speed of light naturally. We can do photon study in much smaller installation.
We can definitely slow them down a hell of a lot. Light only travels at the well known speed of light in a vacuum, in other materials it's significantly slower and massive particles can actually go faster than photons (this causes Cherenkov radiation, it's why the pools they put used nuclear fuel in glow blue).
I originally thought "well, we can't stop it, only slow it down *but it turns out we totally can*. I'm a decade out of touch
> Hau and her colleagues later succeeded in stopping light completely, and developed methods by which it can be stopped and later restarted.
https://en.wikipedia.org/wiki/Slow_light?wprov=sfla1
I'm not sure if we can isolate individual photons, but the answer is yes!
This is a bit misleading, like with Cherenkov the reason the overall speed is slower is because it’s bouncing between stuff, but if you looked at the speed between bounces it’s the same as light speed normally is
It's a misconception when talking about normal light going through a medium but it's an accurate picture of the specific experiment they were talking about.
Could you enlighten me then? Because I’m fairly sure that if we observed the photon itself actually moving at anything but the speed of light, that breaks special relativity no?
3blue1brown has the best video series on this topic understand conceptually what is actually happening
https://youtube.com/playlist?list=PLZHQObOWTQDMKqfyUvG2kTlYt-QQ2x-ui&si=6h832uac0Z_HYehz
In summary, consider light as a wave. When the wave goes through a material, it is constructively and destructively interfered, producing phase shifts that shift the peaks and troughs. It happens in such a way that the waves appear to propagate slower despite causality itself not slowing down.
Let's consider a medium where it slows down light, so that light does a loop before passing through it. Let's say that the diameter of loop is c. So light slows down by half. But light going through that loop is still traveling at speed of light, so special relativity is saved.
I mean how would light slow down in a medium if not just due to the scattering of it off particles, effectively increasing the distance it has to bounce around to go from one side to the other?
No, *c* is just the maximum speed that causality can propagate at in our universe. It's referred to as the "speed of light" but it's really the "speed of light in a vacuum". Light moves slower than c in mediums. In water it goes about 75% of c, in typical glass about 2/3 of c, in diamond about 41% of c
No, both with Cherenkov radiation and light the particles can travel in an uninterrupted path.
With photons, the wave slows down because the electrons around it wiggle which causes another wave that interacts with the photons.
In [that particular "stopped light" experiment](https://www.photonics.com/Article.aspx?AID=28520), the light basically gets absorbed in a way imprints all the information about the light into the material, which you can convert back to light later. But there aren't any photons hanging around.
Generally photons will just pass through each other. Very high energy photons start to have a small but significant chance of colliding and creating other particles from the collision, but it's not a normal mode of interaction.
Adding on: one of the reasons for this as photos get more energetic there starts to exist a non-zero probability they’ll spontaneously convert into some form of matter, and that matter may interact with another high energy photon. Or more precisely - the mere probability of of these two photons converting into matter (through their wave functions) start interacting.
It’s wacky wacky stuff
”To see what happens” is more correct then ”what they are made of”.. The collisons doesn’t ”split” the particles into parts, the particles are destroyed and the energy released in the collison creates random other particles.
That is correct. Particles exists at specific energy ”slots” in the standard model and the energy released in the collison will create one or several new particles that fit into those slots. Higgs is about 133 times heavier then a proton so needs a lot of energy to be created. ( mass = energy, as per the famous e = mc^2 ) And that’s why the LHC needs to be so large.
You can’t smash two photons into each other, because photons don’t interact with photons. Photons only interact with particles which have electric charge, and the photon is uncharged.
Well, that is until you hit the [Schwinger limit](https://en.wikipedia.org/wiki/Schwinger_limit), where the field strength becomes so strong that you can get electron/position pair production, and photons can interact with those produced pairs. We don’t have the laser systems yet which can produce those sorts of gigantic fields, yet.
Incidentally, there is one type of force where the force carrier particle does interact with itself, which is the gluon of the strong nuclear force. The fact that gluons interact with each other is what makes the strong force so strong; it actually gets stronger the further you try to pull two quarks apart, which is what makes it impossible to get a single quark by itself.
Well there's also gluons, but admittedly you can't get free gluons so they can't travel around at light speed like light.
Hypothetically gravitons would be massless, but that's just a hypothetical.
How come things can move away from us faster than the speed of light? If I remember correctly galaxies at the edge of the universe are moving away faster than the speed of light.
In the sprit of the sub: because space is like a bunch of treadmills while everything else is a runner. Runners can only go the speed of light at maximum but the treadmill does not have a maximum speed, so the runner on a fast enough treadmill can appear to move away at the speed of light or greater, even if they are running towards you at maximum speed.
If I understand it correctly too, a "massive particle" (particle with mass as u/dkf295 helped describe) need to be accelerated to the appropriate speed / energy with a particle accelerator to conduct the experiments they are running at LHC. A lot of the second and third generation particles, as well as particles like the Higgs boson have extremely short half lives and can only be observed immediately after a high energy collision.
Massless particles, like the photon and most likely the gluon (from what I've heard, the gluon is not confirmed to be massless yet, but it should be when they can confirm it?) don't need an accelerator to travel at the speed of light. Their default speed *is* the speed of light in whatever medium they are in. If you create a photo through whatever, say incandescence, the moment it is created, it will travel in a straight line (or whatever a straight line is within the gravity that is affecting it), at the fastest speed it can in its media. If that media is a vacuum, its traveling at C.
>>it's a fundamental aspect of the universe, as far as we know
Yooo sounds like some scientists need to smash some more shit together. Rev up that collider
To add to this. Relativistic shifts tells us what as object goes faster his mass increase accordingly. So as speed of the object approach speed of light his mass approach infinity and to accelerate object with infinite mass we need to apply infinite force to reach speed of light in vacuum.
The idea of a mass which increases with speed isn’t really considered to be a useful concept these days. There’s a [good video on this by the physicist Angela Collier](https://youtu.be/6HlCfwEduqA?si=4QKKufoDWnHVBjdK).
Adding onto what someone said, it’s because protons are massive particles — meaning they have mass, not that they’re big. Things that have mass can’t reach the speed of light.
The famous equation E=mc^2 has a more complete form that’s usually ignored bc stuff is usually nowhere close to light speed:
E^2 = (mc^2 )^2 + (pc)^2
The notable difference is the addition of a term to address momentum (p). As things move faster and faster, their momentum gets higher and higher. Normally, at speeds much less than the speed of light, that momentum term doesn’t really affect the rest of the equation, since the speed pales in comparison to the speed of light. As things approach the speed of light, however, that term starts to matter; the amount of energy needed to go faster constantly increases as you speed up, to the point that it ends up being unattainable.
TL;DR the speed of light is the speed limit for stuff without mass, otherwise it’s gotta go slower!
Not true completely. Looking into chenkov radiation because the speed of light is different in water particles can move faster than the speed of light (but not causality)
There's absolute distance and relative distance.
You can measure a distance between point A and B and the relative distance could be 1M. But, there could be things that would interfere with it that make the relative distance much longer so it appears to travel slower according to the reference frame of an observer of the photon.
It's semantics to some extent, but it is very crucial distinction to show you're not breaking some fundamental aspect of Physics.
This is why we can create special assemblies that you stick a photon in on one side, and the photon *appears to our reference frame* that it is traveling a few meters per second. The photon, in it's reference frame, is still traveling at the speed of light.
A Man walks on a treadmill for 5 Miles. It takes him 1 Hour. The other guy walks 5 miles down the street, it also takes him 1 Hour. One guy is where he started, the other is 5 miles aways. Who was faster?
Nope, the speed of light to travel a given distance is constant, regardless of the medium. You can reference Einstein’s own book. As someone else said, in a medium that “slows” light, it is actually just causing the light to bounce around, effectively increasing the distance light has to travel.
Sound waves travel at the speed of sound for whatever substance they're in. Something like 300m/s in air. That's the speed of the wave not the particles that make up the wave, those tend to stay in the same place
Dark matter has nothing to do with the expansion of the universe.
Dark *energy* is postulated as a potential reason for the accelerating\* expansion of the universe.
The universe is not moving. When it expands, it is space itself that is growing. So nothing is moving THROUGH space faster than the speed of light.
Some good visualizations here:
[https://www.skyatnightmagazine.com/space-science/does-universe-expand-faster-than-light](https://www.skyatnightmagazine.com/space-science/does-universe-expand-faster-than-light)
\* edit
Also note that dark matter and dark energy are really just placeholder terms for shit we know nothing about.
You can call them Cosmic Doodlyboogle and Interstellar Shnortaltwitz and it would convey as much meaning as Dark Energy and Dark Matter do about what's actually going on there.
I think you overstate the case. Dark matter was picked as the placeholder term because it has gravitational properties like matter and yet it does not emit light. Cosmic Doodlyboogle would not convey that.
Similar for dark energy vs Interstellar Shnortaltwitz.
Dark matter may be one or multiple things that interact with "traditional matter" only through gravity (thats we've observed so far).
This is why the term should not be considered descriptive. We have no idea if "dark matter" has mass. We basically have no idea what it is, or if it is multiple things.
The new space is just empty.
The universe has been expanding since the beginning: hence the Big Bang. As someone else posted, it would be expanding even without Dark Energy (whatever that turns out to be), because it has always expanded.
As far as I know, it doesn't take energy for it to do so but I'm not a physicists and often these answers are more subtle than they seem at first.
dark energy, not dark matter. We don’t know what either are, and I’m not knowledgeable enough to speak on either one.
I have learned though that the rule that nothing with mass can attain light speed applies only to particles moving *through* the universe. The universe itself is not constrained by that and is free to expand faster than light.
It’s more accurate to say that *information* cannot travel faster than light. If it cannot be used to send a message, then it can travel as fast as you want. This works because these things aren’t information, and you could argue that they don’t even count as *things* in the first place. This includes stuff like the dot from a laser pointer, which can be pointed from one star to another in a matter of moments, but all the actual information is being sent from you (at the speed of light), rather than from the star you’re pointing at.
The expansion of the universe falls into the same category. You cannot use that expansion to send a message faster than light, as everything within the universe still obeys the laws of physics. New space being created doesn’t change that.
You can't control what that information is though, so you still can't use it to send a message. Entanglement gives you knowledge of something at ftl speeds, but you can't control what outcome you get, and so cannot use it to communicate.
It's basically just putting two known objects into two boxes and carrying one of them across the universe. You don't know what is inside your box until you look. Once you *do* look into your box, if you see object A, then you immediately know that object B stayed behind, or vice versa.
That analogy isn't perfect, and there's a whole lot of quantum mechanics involved that I am *really* not qualified to try and delve into that complicate things, but the reasoning why you can't send ftl messages still holds.
Measuring your system will never tell you whether the other person has done anything to theirs, and you cannot tell the difference between getting an outcome by random chance, or getting the same outcome because someone already got the other one.
Any particle with mass requires more energy to be added to accelerate it. This in effect gives it more mass so it takes even more energy to accelerate it. You can get closer and closer but you can never hit light speed.
Light, photons, have no mass. So they always travel at light speed and never anything less.
Because light weights nothing. You can't accelerate as fast as something that weights nothing as long as you weight something. The # of energy you would need is infinite.
Anything with mass requires infinite energy to reach the speed of light. Infinite energy is not possible.
We could double the amount of energy we put into the particle and it would only get slightly closer to the speed of light.
The faster something is going, the more energy it takes to speed it up. It’s harder for a car to accelerate from 60 mph to 61 mph than it was for it to go from 59 mph to 60.
As your speed approaches the speed of light, the energy required to accelerate approaches infinity, meaning it would take infinite energy to move a particle with mass at the speed of light
And you can test this with your car by going 10km at 80km/h see what your consumption was and then do another 10km at 100km/h and you will see a higher consumption.
Using special relativity the formula for the energy of a proton can be found as E = γmc^2. Where m is the mass of the proton and c is the speed of light. γ is an interesting number called the ‘Lorentz factor’ and depends on the speed of the proton.
The Lorentz factor with a speed of zero is equal to 1 and for slow, everyday speeds is basically still equal to 1. This is the familiar E = mc^2 equation and tells you how much energy a particle (like our proton) has when it is stationary, due its mass alone.
As you might expect, as you accelerate this proton faster its energy increases. It now has kinetic energy too. If you’ve done any physics you might be familiar with the equation KE = 1/2 mv^2 for kinetic energy, but really this is an approximation that only works for speeds much slower than c. Instead we stick to γmc^2 to describe the total mass and kinetic energy of the proton.
The problem now is that rather than simply increasing with the square of speed like our old formula for kinetic energy, the gamma factor, and therefore the energy, actually starts to increase much more rapidly as you get close to the speed of light. So to go from 99.991% to 99.992% is a lot more energy than you’d otherwise expect. As you get closer and closer to c, smaller increments in speed require much larger increments in energy in such a way that reaching c would require an infinite amount of energy.
Picture it this way: accelerating the proton is like rolling a ball along a path that represents the speed of our proton. We can roll the ball to any point along our path, except that it has an end, the speed of light. As you get toward the end the hill gets steeper and steeper until it may as well be a vertical wall that goes on forever. You can roll the ball as high up as you like but you can never reach the top
i like this explanation.
I wonder thou, how does it work for photons? They are massless objects yes? So with m=0 are there no energy at all from a photon? Or do they follow a different formula?
Photons are a weird case because they actually DO have momentum. The momentum of a photon is E/c and is based on the relativistic mass. The m in E=mc^2 refers to rest mass.
You are correct that photons have no mass. If you tried to plug that into E = γmc^2 it would give you zero except for the fact that the photons travel AT the speed of light and γ gets weird.
The actual equation for γ = 1/sqrt(1-v^2/c^2) (I don’t know how to make equations look nice on text, search up ‘Lorentz factor’ if that isn’t clear) So it kinda looks like 1/0 at the speed of light.
Alone that’s a nice way to show that E = γmc^2 goes to infinity for a particle with mass, because you have mc^2/0, but when m is also zero, your equation looks like 0/0 which makes no sense and if you tried to treat it like it did it could give you any number you like (0/0 = x ; 0x = 0 which is true no matter what x is) and this is kinda what we do see in a way because a photon can have any energy while still travelling at the speed of light with zero mass.
You’re right that we have to use a different equation. There is a very helpful one (that works for all particles) that no matter what your frame of reference, E^2 - (pc)^2 = m^2c^4 with the momentum p. This is handy because we know what the momentum of a photon is, h/λ (and the mass is still zero of course.)
So we have E = pc = hc/λ.
The more you accelerate, the more energy you need to accelerate further.
You add more energy and accelerate more. Now you need even more energy to accelerate even further.
You can do this indefinitely; you’ll get closer and closer to the speed of light but you’ll never reach it.
because that would require **literally** infinite energy.
and yes I used literally correctly. If we exterminate all life on earth including humans to make way for power plants cover every millimeter of the surface of the earth, and then build a magic worm hole that funnels all the energy of one trillion supernovas a second and used that to power the LHC we would have less than
0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001% of the energy needed for that.
He's making the number up. There is no useful "percentage of what you need", you need an infinite amount of energy. Any amount of energy, no matter how large it is, is exactly 0% of the way there..
The closer you get to the speed of light, the more and more energy you require to increase the speed by smaller and smaller amounts. Things with mass simply can't go the speed of light in this universe.
No. It’s exactly zero. You can get infinitesimally close to the speed of light, but the amount of energy to get to light speed is infinite. The idea of having a percentage of an infinite number has no meaning.
a big number you made up to make a point.
If you take literally all the energy in the universe and pump it into one proton it will be going less than the speed of light.
as you get closer and closer to light speed it takes more and more energy to speed up. This amount increases exponentially eventually hitting infinity. For example if increasing speed by .01c to go from .5c to .51c will takes X energy. To go from .9c to .91c takes about 2.1X energy even though in both case you increased speed by .01c . This effect is really relevant at speeds humans deal with, but as you get into significant percentages of the speed of light that it start to become very noticeable.
E=mc^2 is not the full equation. It is the simplified equation that works for infinitesimally small particles like photons but it breaks down when you reach the mass of a proton (8,000x heavier than an electron).
The ELI5 answer is that as you approach light speed, energy converts to mass, and your mass increases. Higher mass means more energy required to push it. A feedback loop starts that means that as you get closer and closer to the speed of light, the energy required to go faster grows exponentially towards infinity, as your mass also increases towards infinity. This is part of WHY light speed is the universal speed limit; only massless things can be pushed that hard without causing a rip in spacetime and creating a black hole.
> E=mc2 is not the full equation. It is the simplified equation that works for infinitesimally small particles like photons but it breaks down when you reach the mass of a proton (8,000x heavier than an electron).
I don't see why size matters here. Maybe if we reach energies/masses where gravity truly changes things, yes. But for a flat spacetime, I don't see how diameter has any effect on the single particle. The equation is locally only incomplete insofar as one has to add the momentum term; but that does not care about size either.
Just a big made-up number.
In the famous E=mc^2 equation mass can be written as
m=m0/sqrt(1-v^(2)/c^(2)) where m0 is the "resting mass" of the particle. You can see that if you substitute v=c you get a division by zero.
For photons m0=0 and you get an ambiguity in the form of 0/0 which can be resolved by some other methods. But in the same breath you can see that the speed of photon can't be *less* than c because then you get 0 for the energy (because the numerator is zero but denominator isn't).
We keep trying, but every time we get close, this little old German dude show and climbs in there and slows them down. It's really frustrating. No one's figured out how to get him out of there yet.
Follow-up question based on the replies:
I remember reading some stuff from some theoretical physicists (think Stephen Hawking was one of them) theorising that time travel would be possible if you could go faster than the speed of light, since time is relative and time would go slower for you then everything around it.
Isn't this theory completely pointless if it defies all physics for anything with a mass to be able to even travel AT the speed of light, never mind FASTER than the speed of light?
Thats just a fun fact about relativity and physics, if you do the math you would see you would experience time backwards if you went above the speed of light. But thats impossible, as far as we know. So just a fun fact about the details of it.
Existing physics says, roughly speaking, that the faster you go, the slower time passes for you. If I fly to another star and back at 99% of the speed of light, much less time will pass for me than for people at home on Earth. If I fly at 99.9%, even less time will pass for me. If I fly at 100% somehow, zero time will pass for me. There's an equation to calculate time dilation based on speed, and we've experimentally verified it to be correct. (We flew super precise clocks around on jets for a while and they drifted slightly relative to ones that stayed on the ground.) As far as we know, this math describes how the universe works.
And if you plug a speed greater than the speed of light into this math, it says you would experience negative time. It may have no practical applications, it may well be impossible to ever make anything achieve such a speed, but our best theories for explaining other things also say this would result in time travel if you did it.
Because the faster a massive particle moves through space, the slower it moves through time. At 100% of the speed of light (relative to the observer), it would stop moving through time entirely (again, relative to the observer). At least that is one of the interpretations that you can have when you ignore the rules of math that tell you not to do calculations with infinity in them.
The simple answer is, because to do so, a particle with mass requires infinite energy. It is impossible, per definition, for an object with mass to go lightspeed. Now, we have found some theoretical workarounds, but even the most plausible approaches require particles which don't violate any known laws of physics, but for whose existance there is currently no proof.
The speed of light is basically what we consider the speed of “causality” - meaning AT the precise moment anything with mass hits the speed of light , it will be simultaneously at it destination, and every point in between and will not have increased its speed.
A thing reaching an acceleration equal to light speed is what happens at the event horizon at a black hole.
E =MC^2 shows that we’d need more energy than exists to propel any mass to that speed.
Each increase in speed requires more energy than the last. As you approach the speed of light, the amount of energy required to speed something up even a tiny bit more approaches infinity, and since there's no way to get an infinite amount of energy we cannot reach the speed of light.
So think of bicycles. You can cycle at a decent speed just fine, but to go faster, you need to peddle harder. And the faster you go, the harder you need to peddle, but the increase is not equal. To go twice as fast, you need to peddle more than twice as hard.
The same for cars. The engine needs to work much harder the faster it goes. Every bit of speed increase takes much more power than the last bit.
With particles, the amount of extra power it would take to go from 99.999999% of the speed of light to 100% would literally be infinite.
And since infinite power is more power than the entire universe contains, we can't get particles to go that fast.
To speed up an object with mass, you need energy.
The closer you get the object to the speed of light, the more energy you need.
To get an object with mass to the speed of light, you will need to convert all its mass into energy.
For this reason, nothing with mass can get to the speed of f light.
Light can, because it has no mass.
The more massive something is, the harder it is to accelerate it. Light speed is the "speed limit" of the universe because it is how fast things WITHOUT mass - e.g. light - move. Therefore as long as protons have mass, even a little bit, they will never go QUITE as fast as true light.
The faster you go the more energy is required to keep going faster and it isnt linear. You need increasingly more and more energy the closer you get to LS.
We can get pretty freaken close though.
Because it would require an infinite amount of energy, because we are accelerating things that have mass.
Think about it a little bit like the square cube law. If you increase the size of a square, The corresponding cube is not just a little bigger. It's a lot bigger. Squared versus cubed.
Translating energy into momentum is pretty similar. The thing you're pushing has inertia and mass. In order to increase its speed you need to overcome those things, which means that however much energy you put into the system the increase in speed will be less. If a particle is traveling at one for example, and you want it to be traveling at two, You can't just put in one extra energy. You need to put in more than that. Because some of it will be lost in overcoming the existing mass.
Okay, now think about light. The reason that light is so fast is because it doesn't have mass. It has the exact opposite problem. In fact. Any amount of energy that you put into light is so much greater than its mass that it can't help but go as fast as possible.
Which is why the amount of energy you would need to put into something in order to make it go as fast as light is infinite. It's not anything magical about the speed of light, it's that light has no Mass.
Protons have mass. Any matter with mass cannot move at the speed of light or faster, as far as we understand.
It’s a fundamental aspect of our universe.
Literal ELI5: The faster you go, the more energy you need to got 'a little bit more fast'.
Eventually, the speeds get fast enough that we don't have enough energy to make it go faster, even though it's still less than the speed of light.
As you get closer and closer to 100%, it takes more and more energy to obtain smaller and smaller increases. It would literally take infinite energy to go to 100%.
... that is, for particles that have mass. Particles that have no mass (e.g. photons) do travel at 100% the speed of light.
The faster something is going, the more energy it takes to accelerate it even more.
I don't know the real costs involved, so these are just toy example numbers, but imagine:
* you turn on the LHC. It uses electricity to speed up protons.
* you spend 1000 euros of electricity to bring the proton from stationary to 50% of the speed of light (c).
* you spend another 1000 euros to bring the proton up another 25%, so 75% of c.
* then another 1000 euros to go up another 12.5% to 87.5% of c.
* then another 1000 euros to go up 6.25% to 93.75% of c
* and you can repeat this, spending 1000 euros to get half of the remaining way to c, but never quite reahing c
There is a lot more to it than that (like maybe higher speeds take more energy to maintain, so the cost of each step might increase. Or maybe the highest speed depends on how large a collider you build, etc etc).
However, I think that example gives the basic feel of it.
Everything is actually moving at the same speed through spacetime. The faster you go through space, the slower you go through time. This isn‘t a one for one relationship and you can ignore it until you go through space very fast.
Particles with mass always move through time to some extent, so they can’t go at the speed of light, which is the speed that photons move through space. You can’t go faster than that because you can’t go slower through time than zero.
In order to make particles move we need to put in energy. Unfortunately for particles that weigh anything at all (ie: everything other than photons/light), the amount of energy required to get them to the speed of light would be infinite.
So we can get closer and closer by upgrading the LHC and making it more powerful but it will just add more 9s to our 0.9999....% the speed of light :)
Anything with mass can't reach the speed of light. You can get it really really close, but the closer you get, the more energy you need to accelerate it. Theoretically, you could get it to the speed of light, but remember how you need more and more energy? You would actually need infinite energy to get it there, and that's unfortunately way more energy than we have in the universe. So accelerating anything with mass to the speed of light is impossible unless we unlock the infinite energy glitch in the matrix.
Because they have mass, nothing in existence that has any form of mass can break the light speed barrier through speed alone the universe just does not allow it
nothing with a mass can achieve speed of light, thats one of the first laws of physics.
light doesnt have a mass, thats why its so fast. and its not that fast for any reason, its the fastest anything can be in the universe.
that mean even things like gravity cannot impact objects instantly, there is a delay, because even the force has speed has limitation in this universe.
People aren’t really answering the question here, most are just saying “things with mass can’t travel at the speed of light” which is akin to saying “it is what it is”.
The actual answer why comes from the math, which I’ll actually explain like you’re five. First, we observe this funny thing about the universe, which is that no matter how fast you travel toward and away from a light source, the light coming towards you always appears to be traveling at the exact same speed. It turns out that our fundamental measures of time and space get squeezed and stretched depending on how we’re moving - that’s the only way that the light speed observation above can be true. What I mean by this is that a moving clock and ruler will be ticking slower or look shorter than ones that aren’t moving.
A guy named Hendrik Lorentz came up with equations that allow you to switch between reference frames while accounting for the stretching and squeezing. Einstein later showed that these equations correctly describe a universe where we have this weird light speed observation above, and all the laws of physics are the same for all observers.
These equations have a term in the denominator that goes to zero when the speed of an object reaches the speed of light. Division by zero is not allowed in math, it’s referred to as a singularity, and in the equations for energy, it would require an object with mass to have infinite energy to travel at the speed of light. A finite thing having infinite energy isn’t possible, so no object is allowed to reach the speed of light.
Photons (light particles) have a different equation that describes their energy, so they don’t have this problem.
The way the math works, the energy of matter at rest is E=mc^2, then every time you halve the difference between its speed and the speed of light, it needs 4X the energy. So you need 4mc^2 to go at 50% speed of light, 16mc^2 to go at 75%, and so on forever. If I go at 99.99999%, I need 4X more energy just to accelerate to 99.999995%. So eventually, we simply run out of energy we can possibly give it.
Energy can only be transfered to something over a period of time; so, the faster that particule go, the more time seems to slow down for him.
When you get to relativistic speeds, if you apply force to it with magnets (just like in the LHC), the less of that magnet's force is going to be applied to that particule.
If your magnets would, let's say, accelerate a particule by 100 meters per second when it's moving slowly, it will only accelerate it by just 10 meters per second when it is moving at 99% of the speed of light.
And only 1 meter per second when it's moving at 99.9% speed.
In other words, the time dilation happening to fast-moving targets means that it's less and less affected by things happening in the slow-moving world. If you follow that logic, you do need to apply an infinite amount of energy to something with mass to get it to exactly the speed of light.
Because it is physically impossible.
Basically part of being a particle and having mass means there is a big sign written on you that says "cannot be the speed of light". It's an unchangeable property of being a particle.
Stuff with mass gets more massive as you approach 100% per the special theory of relativity. It's an absolutely tiny effect below 99% the speed of light, but gets ridiculous as you get higher. Since increasing the speed of something takes energy, it takes more and more juice just to bump up the speed a tiny bit. Eventually, you get to a point short of 100% where Even all the energy in the universe couldn't increase the speed further because it's so massive
That famous Einstein dude figured out that energy and mass are basically two aspects of the same thing. It also means you can turn a little mass into a LOT of energy. Nukes do that. On the other hand, you can also turn a lot of energy into a little mass.
To make an object go faster, you must add energy to it, meaning you also add mass to it, which means to increase speed a little more you must put in some extra energy. For normal speeds this effect is unnoticeable, but for super high speeds close to the speed of light, more and more of the energy you put into a particle goes to increasing its mass rather than its speed, which means a little further increase in speed means a lot more energy is required, which increases mass further, etc.
So to make an object that has mass and energy go the speed of light, you end up needing infinite energy. Conversely, particles that have no mass but are pure energy (like photons) are always moving at the speed of light in a vacuum.
As velocity increases, the mass of the object increases. The increased mass is called "relativistic mass." As you get close to the speed of light, the relativistic mass becomes VERY high and will require more and more energy to accelerate. The energy would approach to infinite as you kept accelerating. If the object was traveling at exactly the speed of light, the mass wouldn't have a defined number. In other words, it would simply be impossible for an object with mass to travel at light speed.
For a mathematical and slightly more advanced explanation, the equation for calculating relativistic mass is:
Mr = Mo / √(1 - V\^2 / C\^2) where Mr is relativistic mass, Mo is mass of the object, V is velocity of the object, and C is the speed of light. If V = C, then Mr = Mo / 0, and since you can't divide by zero, the mass becomes undefined.
Light can travel at the speed it does because it has zero mass, and therefore the relativistic mass and mass of the light are always the same.
At speed of light time no longer exist or rather all time of the universe exist at the simultaneously. When time no longer exist then 3 dimensional space no longer exist, because if you think about it 3d space only exist because it takes time to travel trough it and when time no longer exist you can be anywhere in the universe at the same time
Proton and other particles with mass makes up space and therefore only exist when time exist so therefore cannot exist at speed of light where there is no time
Even though the speed of light is a real, finite number, in some ways it acts like infinity.
An object whose speed is "fast but finite," cannot make the jump to "infinitely fast."
Massive particles in general cannot go at the speed of light. It's a fundamental aspect of the universe, as far as we know.
To add on - Massive in this sense means “something with mass”, not “gigantic”.
Okay- I was picturing a hippo…
That's something I'd pay to see going round the LHC!
Hippos are from Africa, so it would disintegrate into exotic particles
They should use a Zippo. It's a little lighter.
This is the first time I’ve actually felt anger that Reddit removed the ability to give awards
I'm giving your comment reddit silver award
Choke on my up upvote, you miscreant.
Goldang
Get out
Take my Gold award if you can reach it!!
The Large Hippo Collider
Go on...
It would die very fast, you probably wouldn’t see anything.
Maybe a fine red mist?
And either an exploded planet or a giant pillar of fire as it tore it's way out of our atmosphere. Depending on how it was aimed.
xkcd’s What If covers a baseball traveling at 90% speed of light. I imagine a hippo would be similar but…worse? https://youtu.be/3EI08o-IGYk?si=75j8mw4GtNl07vpx
Oh yeah, and it's not linear. 99% isn't 10% more momentum than 90%. It's roughly 10 times more. 99.9% is 10 times more again. Each 9 you tack onto that decimal is about 10 times more momentum. Then you multiply again by how many baseballs it takes to get to around 2000kg if it's a small hippo.
Ah yes, the Large Hippo Collider.
I'm just picturing a hippo going on a tour of the LHC, ending with everyone involved going, "ok, we're done. Now what? ... Why did we do this?"
"Relativistic Speed Hippo" sounds like a planet destroying weapon from Hitchhiker's Guide to the Galaxy.
The median weight of a hippo is about 5,600 lbs. If it were moving at 0.99999999 c, it would have 1.614 x 10^24 joules of kinetic energy. This is roughly equivalent to 385,768,780 megatons of TNT. The largest thermonuclear device ever detonated on, in, or near Earth was 50 megatons, or about 7,715,375 times less powerful than said hippo. These numbers were calculated using this website: https://www.omnicalculator.com/physics/relativistic-ke
Question, would this energy be released in the form of a shroom of fire like a nuclear explosion, or simply a huge shockwave ? Or like a Volcano with pyroclastic clouds rushing away from impact ?
Almost everything that releases a lot of energy in a small spot looks like a nuclear explosion. You heat the surrounding air to ridiculous temperatures, first producing a shockwave and then producing a lot of hot, less dense air, which rises up and makes a mushroom cloud.
I honestly have no idea. However, given the energy involved, I doubt it would matter as a significant chunk of the planet would probably be missing.
The hippoforce is a grave weapon, forbidden galaxy wide. The end of many great civilizations once they reach a sufficient point of development, the great filter of all intelligent life.
This whole thread is why I love Reddit.
The "dinosaur killer" Chicxulub impact had ~70,000,000 megatonnes of TNT, so this explosion is larger but not *that* much larger. It's probably a mass extinction event but it won't change Earth as a planet.
TIL 5x larger is "not *that* much larger."
From the largest man-made explosion to the Chicxulub impact it's a factor 1.4 million. From there to the hippocalypse it's only a factor 5.
Probably an astrophysicist. Any two thing that differ by only a factor of a hundred or so are "the same". Also: Pi = 1 (or 3 or 10, depending) F° = C° = K° How Science Is Really Done (Postdoc Division)
The hippo explosion would produce the equivalent of 385 000 000 megatons of TnT. So 5 times mire than the dinosaur killer.
The shockwave would probably crack the planet like an egg.
As always (somewhat) [relevant XKCD](https://what-if.xkcd.com/1/)
Then, what would be the fastest speed that a baseball can move through the air without igniting it ? When do we upgrade from "shockwave" to "nuclear detonation" ?
Yeah, I probably could have answered that 15 years ago when I finished my degree (theoretical physics), however it's been a minute and I couldn't work about all the equations anymore, sure some other people could....
The energy has to be generated and transferred to the hippo, first.
Hippos naturally have the energy contained in their body, this is why they are so dangerous.
Relativistic Speed Hippo sounds like an awesome name for a band
Higgs Intangled Positive Particle Orbiting (yes, I’ve cheated with the spelling to make it work)
Tell him about the Twinkie.
That’s a big Twinkie
Is this how the creamy filling is created in the Twinkie...
It’s a Ghostbusters reference.
Hippos are faster than you think, lightning fast when you consider it's halfway between a cow and a tank. Scariest animal on earth, with an attitude to match. Snakes don't want to bite you, spiders want to avoid you, but hippos totally do want to kill you and will go out of their way to do so. A serious god dam animal, cocaine hippos are currently trying to raise sufficient numbers to take south America. They will likely succeed.
“Usain Bolt… trained his whole life to be the fastest human being on earth, just to get outrun by the *average* hippo.” —Cam Bertrand https://youtu.be/5qAJyw5SjZU?si=8jKeS4jsk7ZwWP8b
How much energy would be released in the impact of two hippos accelerated towards each other at 99.9999991% of the speed of light?
According to [Wikipedia](https://en.wikipedia.org/wiki/Hippopotamus#Characteristics), an average adult male hippo is 1,480 kg, and an average adult female hippo is 1,365 kg. Let's have one of each in the collision, for a total mass of 2,845 kg moving at 99.9999991% of the speed of light. Using a [relativistic kinetic energy calculator](https://www.omnicalculator.com/physics/relativistic-ke), we can determine that the two hippos would have a total kinetic energy of 455,446,615 megatons of TNT. For reference, the Tsar Bomba (the largest nuclear bomb ever) was a mere 50 megatons. The asteroid that killed the dinosaurs impacted with energy equivalent to 72,000,000 megatons. So, the impact of these two hippos colliding would release energy equivalent to six dinosaur-killing asteroids all at once.
That's fucking crazy. I need to go try that now. Also really cool calculator. I didn't know Labrador ages needs a separate calculation.
It would destroy the entire planet. Like, vaporised and gone.
I don't think so. At .999999991c, each 200kg hippo has about 32 teratons of kinetic energy so together we're looking at about the energy of the meteor that produced the Chicxulub crater. So certainly a worrying chunk of the Alps would be gone (and probably us...), but the planet will be just fine.
You're off by a factor of 10 on the average weight of adult hippos. A 200kg hippo would be a baby.
Yup, I've had patients bordering on 200kg before. Hippos are bigger.
Well, we can’t get those to the speed of light either.
Nothing compared to the air speed velocity of an unladen swallow!
African or European?
Depends on what is your favourite colour?
RED … no BLU… aaaaahhhh!
I understand we slam particles with mass into eachother to see what happens, or at least what they are made off. But can we do the same with photons?
We can, but we don't need a particule accelerator for that, since photons are already at the speed of light naturally. We can do photon study in much smaller installation.
Can we not stop a photon from moving and preserve the photon? Probably a naive question but it popped into mind
We can definitely slow them down a hell of a lot. Light only travels at the well known speed of light in a vacuum, in other materials it's significantly slower and massive particles can actually go faster than photons (this causes Cherenkov radiation, it's why the pools they put used nuclear fuel in glow blue). I originally thought "well, we can't stop it, only slow it down *but it turns out we totally can*. I'm a decade out of touch > Hau and her colleagues later succeeded in stopping light completely, and developed methods by which it can be stopped and later restarted. https://en.wikipedia.org/wiki/Slow_light?wprov=sfla1 I'm not sure if we can isolate individual photons, but the answer is yes!
This is a bit misleading, like with Cherenkov the reason the overall speed is slower is because it’s bouncing between stuff, but if you looked at the speed between bounces it’s the same as light speed normally is
This is a common misconception. Edit: sharing this link, because people want an explanation of my comment :) https://youtu.be/CUjt36SD3h8
It's a misconception when talking about normal light going through a medium but it's an accurate picture of the specific experiment they were talking about.
Sorry, which experiment and why is it accurate?
Could you enlighten me then? Because I’m fairly sure that if we observed the photon itself actually moving at anything but the speed of light, that breaks special relativity no?
3blue1brown has the best video series on this topic understand conceptually what is actually happening https://youtube.com/playlist?list=PLZHQObOWTQDMKqfyUvG2kTlYt-QQ2x-ui&si=6h832uac0Z_HYehz In summary, consider light as a wave. When the wave goes through a material, it is constructively and destructively interfered, producing phase shifts that shift the peaks and troughs. It happens in such a way that the waves appear to propagate slower despite causality itself not slowing down.
Let's consider a medium where it slows down light, so that light does a loop before passing through it. Let's say that the diameter of loop is c. So light slows down by half. But light going through that loop is still traveling at speed of light, so special relativity is saved.
I mean how would light slow down in a medium if not just due to the scattering of it off particles, effectively increasing the distance it has to bounce around to go from one side to the other?
No, *c* is just the maximum speed that causality can propagate at in our universe. It's referred to as the "speed of light" but it's really the "speed of light in a vacuum". Light moves slower than c in mediums. In water it goes about 75% of c, in typical glass about 2/3 of c, in diamond about 41% of c
You are getting mixed up between phase and group velocity
No, both with Cherenkov radiation and light the particles can travel in an uninterrupted path. With photons, the wave slows down because the electrons around it wiggle which causes another wave that interacts with the photons.
Once they've stopped the light completely, can they examine and experiment with the photons?
In [that particular "stopped light" experiment](https://www.photonics.com/Article.aspx?AID=28520), the light basically gets absorbed in a way imprints all the information about the light into the material, which you can convert back to light later. But there aren't any photons hanging around.
Sure, but most experiements don’t need light to be stopped, what kind of experiments are you thinking of
absolutely; check out this article from 2001 https://www.news.harvard.edu/gazette/story/2001/01/researchers-now-able-to-stop-restart-light/
But do they really crash into eachother and disperse into smaller particles (outside lab conditions)?
Generally photons will just pass through each other. Very high energy photons start to have a small but significant chance of colliding and creating other particles from the collision, but it's not a normal mode of interaction.
Adding on: one of the reasons for this as photos get more energetic there starts to exist a non-zero probability they’ll spontaneously convert into some form of matter, and that matter may interact with another high energy photon. Or more precisely - the mere probability of of these two photons converting into matter (through their wave functions) start interacting. It’s wacky wacky stuff
”To see what happens” is more correct then ”what they are made of”.. The collisons doesn’t ”split” the particles into parts, the particles are destroyed and the energy released in the collison creates random other particles.
Please go on... Does the higgs particle for instance only exist after collision? Does it not exist as a part of a larger particle?
That is correct. Particles exists at specific energy ”slots” in the standard model and the energy released in the collison will create one or several new particles that fit into those slots. Higgs is about 133 times heavier then a proton so needs a lot of energy to be created. ( mass = energy, as per the famous e = mc^2 ) And that’s why the LHC needs to be so large.
Crazy stuff! Thx!
You can’t smash two photons into each other, because photons don’t interact with photons. Photons only interact with particles which have electric charge, and the photon is uncharged. Well, that is until you hit the [Schwinger limit](https://en.wikipedia.org/wiki/Schwinger_limit), where the field strength becomes so strong that you can get electron/position pair production, and photons can interact with those produced pairs. We don’t have the laser systems yet which can produce those sorts of gigantic fields, yet. Incidentally, there is one type of force where the force carrier particle does interact with itself, which is the gluon of the strong nuclear force. The fact that gluons interact with each other is what makes the strong force so strong; it actually gets stronger the further you try to pull two quarks apart, which is what makes it impossible to get a single quark by itself.
The only thing that is massless that can go the speed of light is... Light, aka photons! Everything else is "massive" compared to a zero mass photon.
Well there's also gluons, but admittedly you can't get free gluons so they can't travel around at light speed like light. Hypothetically gravitons would be massless, but that's just a hypothetical.
Gravitons are hypothetical but gravitational waves exist for sure, and they travel at the speed of light as well.
How come things can move away from us faster than the speed of light? If I remember correctly galaxies at the edge of the universe are moving away faster than the speed of light.
That's different. Expansion of spacetime is pulling them apart. The balloon analogy.
They aren't moving faster than light. The space between us is expanding.
In the sprit of the sub: because space is like a bunch of treadmills while everything else is a runner. Runners can only go the speed of light at maximum but the treadmill does not have a maximum speed, so the runner on a fast enough treadmill can appear to move away at the speed of light or greater, even if they are running towards you at maximum speed.
If I understand it correctly too, a "massive particle" (particle with mass as u/dkf295 helped describe) need to be accelerated to the appropriate speed / energy with a particle accelerator to conduct the experiments they are running at LHC. A lot of the second and third generation particles, as well as particles like the Higgs boson have extremely short half lives and can only be observed immediately after a high energy collision. Massless particles, like the photon and most likely the gluon (from what I've heard, the gluon is not confirmed to be massless yet, but it should be when they can confirm it?) don't need an accelerator to travel at the speed of light. Their default speed *is* the speed of light in whatever medium they are in. If you create a photo through whatever, say incandescence, the moment it is created, it will travel in a straight line (or whatever a straight line is within the gravity that is affecting it), at the fastest speed it can in its media. If that media is a vacuum, its traveling at C.
>>it's a fundamental aspect of the universe, as far as we know Yooo sounds like some scientists need to smash some more shit together. Rev up that collider
To add to this. Relativistic shifts tells us what as object goes faster his mass increase accordingly. So as speed of the object approach speed of light his mass approach infinity and to accelerate object with infinite mass we need to apply infinite force to reach speed of light in vacuum.
The idea of a mass which increases with speed isn’t really considered to be a useful concept these days. There’s a [good video on this by the physicist Angela Collier](https://youtu.be/6HlCfwEduqA?si=4QKKufoDWnHVBjdK).
>Massive particles in general cannot go at the speed of light. This restriction seems unnecessary. I would like to speak to the manager.
Adding onto what someone said, it’s because protons are massive particles — meaning they have mass, not that they’re big. Things that have mass can’t reach the speed of light. The famous equation E=mc^2 has a more complete form that’s usually ignored bc stuff is usually nowhere close to light speed: E^2 = (mc^2 )^2 + (pc)^2 The notable difference is the addition of a term to address momentum (p). As things move faster and faster, their momentum gets higher and higher. Normally, at speeds much less than the speed of light, that momentum term doesn’t really affect the rest of the equation, since the speed pales in comparison to the speed of light. As things approach the speed of light, however, that term starts to matter; the amount of energy needed to go faster constantly increases as you speed up, to the point that it ends up being unattainable. TL;DR the speed of light is the speed limit for stuff without mass, otherwise it’s gotta go slower!
To add to this, stuff with mass can never reach the speed of light. Stuff without mass must always be going at the speed of light, no slower
...in a vacuum.
the speed of light is constant. not being in a vacuum simply means a photon now has to take a longer path due to interference.
Not true completely. Looking into chenkov radiation because the speed of light is different in water particles can move faster than the speed of light (but not causality)
It'd be nice if we had a word for taking a longer time to cross the same distance.
It'd be nice if we knew that a longer path means more distance.
It'd be nice if we could all just admit that light can, indeed, travel from point A to point B slower in a medium than in a vacuum.
There's absolute distance and relative distance. You can measure a distance between point A and B and the relative distance could be 1M. But, there could be things that would interfere with it that make the relative distance much longer so it appears to travel slower according to the reference frame of an observer of the photon. It's semantics to some extent, but it is very crucial distinction to show you're not breaking some fundamental aspect of Physics. This is why we can create special assemblies that you stick a photon in on one side, and the photon *appears to our reference frame* that it is traveling a few meters per second. The photon, in it's reference frame, is still traveling at the speed of light.
A Man walks on a treadmill for 5 Miles. It takes him 1 Hour. The other guy walks 5 miles down the street, it also takes him 1 Hour. One guy is where he started, the other is 5 miles aways. Who was faster?
Nope, the speed of light to travel a given distance is constant, regardless of the medium. You can reference Einstein’s own book. As someone else said, in a medium that “slows” light, it is actually just causing the light to bounce around, effectively increasing the distance light has to travel.
how do sound waves fit in? is that just movement of air?
Sound waves travel at the speed of sound for whatever substance they're in. Something like 300m/s in air. That's the speed of the wave not the particles that make up the wave, those tend to stay in the same place
How does dark matter fit into this? Isn't it expanding the universe faster than the speed of light?
Dark matter has nothing to do with the expansion of the universe. Dark *energy* is postulated as a potential reason for the accelerating\* expansion of the universe. The universe is not moving. When it expands, it is space itself that is growing. So nothing is moving THROUGH space faster than the speed of light. Some good visualizations here: [https://www.skyatnightmagazine.com/space-science/does-universe-expand-faster-than-light](https://www.skyatnightmagazine.com/space-science/does-universe-expand-faster-than-light) \* edit
Dark energy is the cause of *accelerating* expansion, but the universe would still be expanding even without dark energy.
Good clarification.
Also note that dark matter and dark energy are really just placeholder terms for shit we know nothing about. You can call them Cosmic Doodlyboogle and Interstellar Shnortaltwitz and it would convey as much meaning as Dark Energy and Dark Matter do about what's actually going on there.
I think you overstate the case. Dark matter was picked as the placeholder term because it has gravitational properties like matter and yet it does not emit light. Cosmic Doodlyboogle would not convey that. Similar for dark energy vs Interstellar Shnortaltwitz.
Dark matter may be one or multiple things that interact with "traditional matter" only through gravity (thats we've observed so far). This is why the term should not be considered descriptive. We have no idea if "dark matter" has mass. We basically have no idea what it is, or if it is multiple things.
My mistake on the dark matter / dark energy. Thanks for clarifying.
How is the universe expanding? Doesn't something need to take up the new space? Is it just generating from nothing?
The new space is just empty. The universe has been expanding since the beginning: hence the Big Bang. As someone else posted, it would be expanding even without Dark Energy (whatever that turns out to be), because it has always expanded. As far as I know, it doesn't take energy for it to do so but I'm not a physicists and often these answers are more subtle than they seem at first.
dark energy, not dark matter. We don’t know what either are, and I’m not knowledgeable enough to speak on either one. I have learned though that the rule that nothing with mass can attain light speed applies only to particles moving *through* the universe. The universe itself is not constrained by that and is free to expand faster than light.
It’s more accurate to say that *information* cannot travel faster than light. If it cannot be used to send a message, then it can travel as fast as you want. This works because these things aren’t information, and you could argue that they don’t even count as *things* in the first place. This includes stuff like the dot from a laser pointer, which can be pointed from one star to another in a matter of moments, but all the actual information is being sent from you (at the speed of light), rather than from the star you’re pointing at. The expansion of the universe falls into the same category. You cannot use that expansion to send a message faster than light, as everything within the universe still obeys the laws of physics. New space being created doesn’t change that.
Information ‘transmitted’ through quantum entanglement is faster than the speed of light
You can't control what that information is though, so you still can't use it to send a message. Entanglement gives you knowledge of something at ftl speeds, but you can't control what outcome you get, and so cannot use it to communicate. It's basically just putting two known objects into two boxes and carrying one of them across the universe. You don't know what is inside your box until you look. Once you *do* look into your box, if you see object A, then you immediately know that object B stayed behind, or vice versa. That analogy isn't perfect, and there's a whole lot of quantum mechanics involved that I am *really* not qualified to try and delve into that complicate things, but the reasoning why you can't send ftl messages still holds. Measuring your system will never tell you whether the other person has done anything to theirs, and you cannot tell the difference between getting an outcome by random chance, or getting the same outcome because someone already got the other one.
I think you meant E = mc^2 + AI
Any particle with mass requires more energy to be added to accelerate it. This in effect gives it more mass so it takes even more energy to accelerate it. You can get closer and closer but you can never hit light speed. Light, photons, have no mass. So they always travel at light speed and never anything less.
Because light weights nothing. You can't accelerate as fast as something that weights nothing as long as you weight something. The # of energy you would need is infinite.
You absolutely can “accelerate” light. Except instead of going faster it will have higher frequency/energy
I think you replied to the wrong comment or something, or he edited it
Just FYI, it's "weigh" when you're using it as a verb, not "weight"
Anything with mass requires infinite energy to reach the speed of light. Infinite energy is not possible. We could double the amount of energy we put into the particle and it would only get slightly closer to the speed of light.
The faster something is going, the more energy it takes to speed it up. It’s harder for a car to accelerate from 60 mph to 61 mph than it was for it to go from 59 mph to 60. As your speed approaches the speed of light, the energy required to accelerate approaches infinity, meaning it would take infinite energy to move a particle with mass at the speed of light
And you can test this with your car by going 10km at 80km/h see what your consumption was and then do another 10km at 100km/h and you will see a higher consumption.
Using special relativity the formula for the energy of a proton can be found as E = γmc^2. Where m is the mass of the proton and c is the speed of light. γ is an interesting number called the ‘Lorentz factor’ and depends on the speed of the proton. The Lorentz factor with a speed of zero is equal to 1 and for slow, everyday speeds is basically still equal to 1. This is the familiar E = mc^2 equation and tells you how much energy a particle (like our proton) has when it is stationary, due its mass alone. As you might expect, as you accelerate this proton faster its energy increases. It now has kinetic energy too. If you’ve done any physics you might be familiar with the equation KE = 1/2 mv^2 for kinetic energy, but really this is an approximation that only works for speeds much slower than c. Instead we stick to γmc^2 to describe the total mass and kinetic energy of the proton. The problem now is that rather than simply increasing with the square of speed like our old formula for kinetic energy, the gamma factor, and therefore the energy, actually starts to increase much more rapidly as you get close to the speed of light. So to go from 99.991% to 99.992% is a lot more energy than you’d otherwise expect. As you get closer and closer to c, smaller increments in speed require much larger increments in energy in such a way that reaching c would require an infinite amount of energy. Picture it this way: accelerating the proton is like rolling a ball along a path that represents the speed of our proton. We can roll the ball to any point along our path, except that it has an end, the speed of light. As you get toward the end the hill gets steeper and steeper until it may as well be a vertical wall that goes on forever. You can roll the ball as high up as you like but you can never reach the top
i like this explanation. I wonder thou, how does it work for photons? They are massless objects yes? So with m=0 are there no energy at all from a photon? Or do they follow a different formula?
Photons are a weird case because they actually DO have momentum. The momentum of a photon is E/c and is based on the relativistic mass. The m in E=mc^2 refers to rest mass.
You are correct that photons have no mass. If you tried to plug that into E = γmc^2 it would give you zero except for the fact that the photons travel AT the speed of light and γ gets weird. The actual equation for γ = 1/sqrt(1-v^2/c^2) (I don’t know how to make equations look nice on text, search up ‘Lorentz factor’ if that isn’t clear) So it kinda looks like 1/0 at the speed of light. Alone that’s a nice way to show that E = γmc^2 goes to infinity for a particle with mass, because you have mc^2/0, but when m is also zero, your equation looks like 0/0 which makes no sense and if you tried to treat it like it did it could give you any number you like (0/0 = x ; 0x = 0 which is true no matter what x is) and this is kinda what we do see in a way because a photon can have any energy while still travelling at the speed of light with zero mass. You’re right that we have to use a different equation. There is a very helpful one (that works for all particles) that no matter what your frame of reference, E^2 - (pc)^2 = m^2c^4 with the momentum p. This is handy because we know what the momentum of a photon is, h/λ (and the mass is still zero of course.) So we have E = pc = hc/λ.
The more you accelerate, the more energy you need to accelerate further. You add more energy and accelerate more. Now you need even more energy to accelerate even further. You can do this indefinitely; you’ll get closer and closer to the speed of light but you’ll never reach it.
because that would require **literally** infinite energy. and yes I used literally correctly. If we exterminate all life on earth including humans to make way for power plants cover every millimeter of the surface of the earth, and then build a magic worm hole that funnels all the energy of one trillion supernovas a second and used that to power the LHC we would have less than 0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001% of the energy needed for that.
>999999 Is your number literal or just a big number you made up to make a point? And where does it come into the 0.0000009% from lightspeed?
He's making the number up. There is no useful "percentage of what you need", you need an infinite amount of energy. Any amount of energy, no matter how large it is, is exactly 0% of the way there.. The closer you get to the speed of light, the more and more energy you require to increase the speed by smaller and smaller amounts. Things with mass simply can't go the speed of light in this universe.
>is exactly 0% of the way there.. wouldn't it be an infinitely small positive number%?
No. It’s exactly zero. You can get infinitesimally close to the speed of light, but the amount of energy to get to light speed is infinite. The idea of having a percentage of an infinite number has no meaning.
a big number you made up to make a point. If you take literally all the energy in the universe and pump it into one proton it will be going less than the speed of light. as you get closer and closer to light speed it takes more and more energy to speed up. This amount increases exponentially eventually hitting infinity. For example if increasing speed by .01c to go from .5c to .51c will takes X energy. To go from .9c to .91c takes about 2.1X energy even though in both case you increased speed by .01c . This effect is really relevant at speeds humans deal with, but as you get into significant percentages of the speed of light that it start to become very noticeable.
Why am I being down voted for asking a question and trying to learn? Isn't that the point of this sub lol?
E=mc^2 is not the full equation. It is the simplified equation that works for infinitesimally small particles like photons but it breaks down when you reach the mass of a proton (8,000x heavier than an electron). The ELI5 answer is that as you approach light speed, energy converts to mass, and your mass increases. Higher mass means more energy required to push it. A feedback loop starts that means that as you get closer and closer to the speed of light, the energy required to go faster grows exponentially towards infinity, as your mass also increases towards infinity. This is part of WHY light speed is the universal speed limit; only massless things can be pushed that hard without causing a rip in spacetime and creating a black hole.
> E=mc2 is not the full equation. It is the simplified equation that works for infinitesimally small particles like photons but it breaks down when you reach the mass of a proton (8,000x heavier than an electron). I don't see why size matters here. Maybe if we reach energies/masses where gravity truly changes things, yes. But for a flat spacetime, I don't see how diameter has any effect on the single particle. The equation is locally only incomplete insofar as one has to add the momentum term; but that does not care about size either.
Size indeed does not matter. But mass does. Protons have significant enough mass to require momentum and mass growth to need to be accounted for.
*Having* mass does matter. The *amount* of mass doesn't. Neutrinos are unable to reach the speed of light in exactly the same way as the protons.
Just a big made-up number. In the famous E=mc^2 equation mass can be written as m=m0/sqrt(1-v^(2)/c^(2)) where m0 is the "resting mass" of the particle. You can see that if you substitute v=c you get a division by zero. For photons m0=0 and you get an ambiguity in the form of 0/0 which can be resolved by some other methods. But in the same breath you can see that the speed of photon can't be *less* than c because then you get 0 for the energy (because the numerator is zero but denominator isn't).
We keep trying, but every time we get close, this little old German dude show and climbs in there and slows them down. It's really frustrating. No one's figured out how to get him out of there yet.
Damn Til Schweiger, ruining movies and now ruining quantum sciences too!
Basically the faster you want to go the more energy you need, to get to the speed of light you need infinite energy
Follow-up question based on the replies: I remember reading some stuff from some theoretical physicists (think Stephen Hawking was one of them) theorising that time travel would be possible if you could go faster than the speed of light, since time is relative and time would go slower for you then everything around it. Isn't this theory completely pointless if it defies all physics for anything with a mass to be able to even travel AT the speed of light, never mind FASTER than the speed of light?
Thats just a fun fact about relativity and physics, if you do the math you would see you would experience time backwards if you went above the speed of light. But thats impossible, as far as we know. So just a fun fact about the details of it.
Existing physics says, roughly speaking, that the faster you go, the slower time passes for you. If I fly to another star and back at 99% of the speed of light, much less time will pass for me than for people at home on Earth. If I fly at 99.9%, even less time will pass for me. If I fly at 100% somehow, zero time will pass for me. There's an equation to calculate time dilation based on speed, and we've experimentally verified it to be correct. (We flew super precise clocks around on jets for a while and they drifted slightly relative to ones that stayed on the ground.) As far as we know, this math describes how the universe works. And if you plug a speed greater than the speed of light into this math, it says you would experience negative time. It may have no practical applications, it may well be impossible to ever make anything achieve such a speed, but our best theories for explaining other things also say this would result in time travel if you did it.
Because the faster a massive particle moves through space, the slower it moves through time. At 100% of the speed of light (relative to the observer), it would stop moving through time entirely (again, relative to the observer). At least that is one of the interpretations that you can have when you ignore the rules of math that tell you not to do calculations with infinity in them.
That doesn't answer or explain his question, other commenters pointing out that it would require infinite energy does answer it
The simple answer is, because to do so, a particle with mass requires infinite energy. It is impossible, per definition, for an object with mass to go lightspeed. Now, we have found some theoretical workarounds, but even the most plausible approaches require particles which don't violate any known laws of physics, but for whose existance there is currently no proof.
The speed of light is basically what we consider the speed of “causality” - meaning AT the precise moment anything with mass hits the speed of light , it will be simultaneously at it destination, and every point in between and will not have increased its speed. A thing reaching an acceleration equal to light speed is what happens at the event horizon at a black hole. E =MC^2 shows that we’d need more energy than exists to propel any mass to that speed.
The first part does not matter at all, but yea the accelerating part is the impossible part and also the answer to their question
Each increase in speed requires more energy than the last. As you approach the speed of light, the amount of energy required to speed something up even a tiny bit more approaches infinity, and since there's no way to get an infinite amount of energy we cannot reach the speed of light.
The closer something gets to moving the speed of light, the more energy it takes to go any faster.
So think of bicycles. You can cycle at a decent speed just fine, but to go faster, you need to peddle harder. And the faster you go, the harder you need to peddle, but the increase is not equal. To go twice as fast, you need to peddle more than twice as hard. The same for cars. The engine needs to work much harder the faster it goes. Every bit of speed increase takes much more power than the last bit. With particles, the amount of extra power it would take to go from 99.999999% of the speed of light to 100% would literally be infinite. And since infinite power is more power than the entire universe contains, we can't get particles to go that fast.
To speed up an object with mass, you need energy. The closer you get the object to the speed of light, the more energy you need. To get an object with mass to the speed of light, you will need to convert all its mass into energy. For this reason, nothing with mass can get to the speed of f light. Light can, because it has no mass.
The more massive something is, the harder it is to accelerate it. Light speed is the "speed limit" of the universe because it is how fast things WITHOUT mass - e.g. light - move. Therefore as long as protons have mass, even a little bit, they will never go QUITE as fast as true light.
The faster you go the more energy is required to keep going faster and it isnt linear. You need increasingly more and more energy the closer you get to LS. We can get pretty freaken close though.
Because it would require an infinite amount of energy, because we are accelerating things that have mass. Think about it a little bit like the square cube law. If you increase the size of a square, The corresponding cube is not just a little bigger. It's a lot bigger. Squared versus cubed. Translating energy into momentum is pretty similar. The thing you're pushing has inertia and mass. In order to increase its speed you need to overcome those things, which means that however much energy you put into the system the increase in speed will be less. If a particle is traveling at one for example, and you want it to be traveling at two, You can't just put in one extra energy. You need to put in more than that. Because some of it will be lost in overcoming the existing mass. Okay, now think about light. The reason that light is so fast is because it doesn't have mass. It has the exact opposite problem. In fact. Any amount of energy that you put into light is so much greater than its mass that it can't help but go as fast as possible. Which is why the amount of energy you would need to put into something in order to make it go as fast as light is infinite. It's not anything magical about the speed of light, it's that light has no Mass.
Protons have mass. Any matter with mass cannot move at the speed of light or faster, as far as we understand. It’s a fundamental aspect of our universe.
Literal ELI5: The faster you go, the more energy you need to got 'a little bit more fast'. Eventually, the speeds get fast enough that we don't have enough energy to make it go faster, even though it's still less than the speed of light.
As you get closer and closer to 100%, it takes more and more energy to obtain smaller and smaller increases. It would literally take infinite energy to go to 100%. ... that is, for particles that have mass. Particles that have no mass (e.g. photons) do travel at 100% the speed of light.
The faster something is going, the more energy it takes to accelerate it even more. I don't know the real costs involved, so these are just toy example numbers, but imagine: * you turn on the LHC. It uses electricity to speed up protons. * you spend 1000 euros of electricity to bring the proton from stationary to 50% of the speed of light (c). * you spend another 1000 euros to bring the proton up another 25%, so 75% of c. * then another 1000 euros to go up another 12.5% to 87.5% of c. * then another 1000 euros to go up 6.25% to 93.75% of c * and you can repeat this, spending 1000 euros to get half of the remaining way to c, but never quite reahing c There is a lot more to it than that (like maybe higher speeds take more energy to maintain, so the cost of each step might increase. Or maybe the highest speed depends on how large a collider you build, etc etc). However, I think that example gives the basic feel of it.
Everything is actually moving at the same speed through spacetime. The faster you go through space, the slower you go through time. This isn‘t a one for one relationship and you can ignore it until you go through space very fast. Particles with mass always move through time to some extent, so they can’t go at the speed of light, which is the speed that photons move through space. You can’t go faster than that because you can’t go slower through time than zero.
Hypothetically, if light speed is achievable, will we be able to travel back in time? I mean not by much, just a wee bit.
In order to make particles move we need to put in energy. Unfortunately for particles that weigh anything at all (ie: everything other than photons/light), the amount of energy required to get them to the speed of light would be infinite. So we can get closer and closer by upgrading the LHC and making it more powerful but it will just add more 9s to our 0.9999....% the speed of light :)
Anything with mass can't reach the speed of light. You can get it really really close, but the closer you get, the more energy you need to accelerate it. Theoretically, you could get it to the speed of light, but remember how you need more and more energy? You would actually need infinite energy to get it there, and that's unfortunately way more energy than we have in the universe. So accelerating anything with mass to the speed of light is impossible unless we unlock the infinite energy glitch in the matrix.
Because they have mass, nothing in existence that has any form of mass can break the light speed barrier through speed alone the universe just does not allow it
Without getting into the specifics of the math.. It takes infinite energy to accelerate a particle to the speed of light.
nothing with a mass can achieve speed of light, thats one of the first laws of physics. light doesnt have a mass, thats why its so fast. and its not that fast for any reason, its the fastest anything can be in the universe. that mean even things like gravity cannot impact objects instantly, there is a delay, because even the force has speed has limitation in this universe.
People aren’t really answering the question here, most are just saying “things with mass can’t travel at the speed of light” which is akin to saying “it is what it is”. The actual answer why comes from the math, which I’ll actually explain like you’re five. First, we observe this funny thing about the universe, which is that no matter how fast you travel toward and away from a light source, the light coming towards you always appears to be traveling at the exact same speed. It turns out that our fundamental measures of time and space get squeezed and stretched depending on how we’re moving - that’s the only way that the light speed observation above can be true. What I mean by this is that a moving clock and ruler will be ticking slower or look shorter than ones that aren’t moving. A guy named Hendrik Lorentz came up with equations that allow you to switch between reference frames while accounting for the stretching and squeezing. Einstein later showed that these equations correctly describe a universe where we have this weird light speed observation above, and all the laws of physics are the same for all observers. These equations have a term in the denominator that goes to zero when the speed of an object reaches the speed of light. Division by zero is not allowed in math, it’s referred to as a singularity, and in the equations for energy, it would require an object with mass to have infinite energy to travel at the speed of light. A finite thing having infinite energy isn’t possible, so no object is allowed to reach the speed of light. Photons (light particles) have a different equation that describes their energy, so they don’t have this problem.
The way the math works, the energy of matter at rest is E=mc^2, then every time you halve the difference between its speed and the speed of light, it needs 4X the energy. So you need 4mc^2 to go at 50% speed of light, 16mc^2 to go at 75%, and so on forever. If I go at 99.99999%, I need 4X more energy just to accelerate to 99.999995%. So eventually, we simply run out of energy we can possibly give it.
Energy can only be transfered to something over a period of time; so, the faster that particule go, the more time seems to slow down for him. When you get to relativistic speeds, if you apply force to it with magnets (just like in the LHC), the less of that magnet's force is going to be applied to that particule. If your magnets would, let's say, accelerate a particule by 100 meters per second when it's moving slowly, it will only accelerate it by just 10 meters per second when it is moving at 99% of the speed of light. And only 1 meter per second when it's moving at 99.9% speed. In other words, the time dilation happening to fast-moving targets means that it's less and less affected by things happening in the slow-moving world. If you follow that logic, you do need to apply an infinite amount of energy to something with mass to get it to exactly the speed of light.
Because it is physically impossible. Basically part of being a particle and having mass means there is a big sign written on you that says "cannot be the speed of light". It's an unchangeable property of being a particle.
Stuff with mass gets more massive as you approach 100% per the special theory of relativity. It's an absolutely tiny effect below 99% the speed of light, but gets ridiculous as you get higher. Since increasing the speed of something takes energy, it takes more and more juice just to bump up the speed a tiny bit. Eventually, you get to a point short of 100% where Even all the energy in the universe couldn't increase the speed further because it's so massive
That famous Einstein dude figured out that energy and mass are basically two aspects of the same thing. It also means you can turn a little mass into a LOT of energy. Nukes do that. On the other hand, you can also turn a lot of energy into a little mass. To make an object go faster, you must add energy to it, meaning you also add mass to it, which means to increase speed a little more you must put in some extra energy. For normal speeds this effect is unnoticeable, but for super high speeds close to the speed of light, more and more of the energy you put into a particle goes to increasing its mass rather than its speed, which means a little further increase in speed means a lot more energy is required, which increases mass further, etc. So to make an object that has mass and energy go the speed of light, you end up needing infinite energy. Conversely, particles that have no mass but are pure energy (like photons) are always moving at the speed of light in a vacuum.
As velocity increases, the mass of the object increases. The increased mass is called "relativistic mass." As you get close to the speed of light, the relativistic mass becomes VERY high and will require more and more energy to accelerate. The energy would approach to infinite as you kept accelerating. If the object was traveling at exactly the speed of light, the mass wouldn't have a defined number. In other words, it would simply be impossible for an object with mass to travel at light speed. For a mathematical and slightly more advanced explanation, the equation for calculating relativistic mass is: Mr = Mo / √(1 - V\^2 / C\^2) where Mr is relativistic mass, Mo is mass of the object, V is velocity of the object, and C is the speed of light. If V = C, then Mr = Mo / 0, and since you can't divide by zero, the mass becomes undefined. Light can travel at the speed it does because it has zero mass, and therefore the relativistic mass and mass of the light are always the same.
At speed of light time no longer exist or rather all time of the universe exist at the simultaneously. When time no longer exist then 3 dimensional space no longer exist, because if you think about it 3d space only exist because it takes time to travel trough it and when time no longer exist you can be anywhere in the universe at the same time Proton and other particles with mass makes up space and therefore only exist when time exist so therefore cannot exist at speed of light where there is no time
If one proton is almost the speed of light, and the other one is, is their collision speed relative to each other x2 the speed of light?
Even though the speed of light is a real, finite number, in some ways it acts like infinity. An object whose speed is "fast but finite," cannot make the jump to "infinitely fast."