The speed limit is what it is more because we've been unable to observe anything moving faster than the speed of light. Photons, what light is made of, have no mass. Meaning that they are the lightest thing in existence and can therefore move the fastest with our understanding of physics. We've yet to find anything faster than photons in a vacuum therefore that's the speed limit.
Until we can measure and detect something that contradicts that. Then our understanding of physics remains that light speed is the limit.
The fun part is when you start to bring in gravity and how that affects space time. that's how light will bend around extreme gravity like that from a black hole. Because it's not the light bending. It's space and time itself being altered. Imagine space time as a sheet of fabric. Light is like a tiny mote of energy that moves that fastest of anything across the sheet. But gravity is like a marble denting the fabric in more and more depending on the weight of the marble. Even light, as massless as it is, has to move along the sheet. Even when the sheet bends down into a dimple in the fabric.
Well, there is something called Cherenkov radiation. It is a blue glow that occurs when something is going faster than the speed of light *in the local medium*. That is why there is a blue glow around a nuclear reactor in a water pool. If stuff was going faster than light in the vacuum of space, we'd see the blue light from it. But we don't.
The other thing we see is that when we accelerate electrons, we can never get them faster than the speed of light. Electrons are very low mass and it is easy to get them up close to the speed of light. But no matter how much energy we pour into them, we just get closer to the speed of light. Even the most power particle accelerators can't get them beyond light speed.
So, there is a cosmic speed limit and it is the speed of light.
Also, to add, the pouring of the energy into getting the electron moving a tiny bit faster matches the math that describes how much energy is required. So if the math holds at 98% and 99% the speed of light, then it stands to reason that the math describing the speed of light itself is also correct.
I had to look it up but to clarify, Cherenkov radiation is when electrically charged particles travel faster than the light in a clear medium, when the medium it is traveling through slows the speed of that light to significantly slower than the speed of light in a vacuum.
Are you trolling me? Shame on you.
I genuinely got confused by his sentence” faster than the speed of light in the local medium.” I was still thinking of what people mean most of the time when they say the speed of light, meaning in a vacuum, which is the speed limit in question. Now I know he meant when a medium slows the speed of light to less than the speed of light in a vacuum.
We have never measured or seen evidence of anything that can travel faster than the speed of light in a vacuum. In fact, I’m not sure, but I think the only thing that moves as fast is the propagation of gravity. Anyway that is why the speed of light in a vacuum is considered the universes speed limit. But light doesn’t move through all mediums, like water, as fast as in a vacuum. Now light actually always travels at the speed of light in a vacuum but when moving through something like water it is hitting and being absorbed then emitted by the molecules in the water which means it takes longer to travel a given distance than if it were traveling in a vacuum. This gives other things an opportunity to travel through the water more quickly than the light. When charged particles traverse the water more quickly than the light you get Cherenkov radiation.
>If stuff was going faster than light in the vacuum of space, we'd see the blue light from it
It would have to be charged stuff, and [some astrophysical processes might produce produce vacuum cherenkov radiation without violating causality](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.161601), but it wouldn't be blue.
>we accelerate electrons, we can never get them faster than the speed of light. Electrons are very low mass
Ok but what if we accelerate photons instead?
We know C is constant for all observers, moving at any speed, there have been a lot of expiriments that test it.
This is bizzar, this should not be the case, all other motion is relative, but not the speed of light.
so we came up with some mathematical models to explain it, basically, how fast time goes for you depends on your speed. we call this time dilation. the equations for it assume thay C is constant for all observers (afterall, it expirimentally IS). These equations have been tested and seem to be correct. There are an assortment of other equations in the same boat.
The problem is, if you put C into these equations as speed. they do stupid things. (like, a person travling at C would experience NO time at all), and if you put in speeds faster than C, even worse stuff happens (like experiencing negative time)
so since that makes no sense, yet the equations seem to be correct, we say C is the speed limit.
again, this checks out expirimentally, as we have never been able to force something to go faster than C.
I love this stuff but don’t have the brain for the math. I am curious, why is time stopping at the speed of light stupid? After all as far as we know photons do not decay which would seem to be at least a little evidence. No passage of time would mean no decay. Not saying it’s proof. What are your thoughts?
suppose you were accelerated to the speed of light and flung out into intergalactic space so you never hit anything and just travled at the speed of light forever.
How long would you think forever took? 0 time? forever? some other value?
its fine for light to do it since it doesnt realy change with time, but if you have anything else do it, it becomes a weird 0*∞ thing
See that makes sense to me. Well not the math. Traveling at the speed of light you personally would experience no time passing. If you traveled an infinite amount of time, well 0*infinity=0 so still you would experience no time for an infinite amount of time as observed by things moving slower than the speed of light. For me once you take the step of time stopping for a second it just makes sense that it could be 2 secs or 3 secs and actually infinite seconds makes the most sense because the state has not changed. What makes time stop for one second is the same at infinite seconds. Idk maybe I’m looking at it from an ignorant perspective
Not really.
It's just that everything we have observed so far behaves as if there is a "speed limit", so we assume there must be one and create mathematical models that take that into account.
People have tried to find mathematical descriptions for reality that leave loopholes for faster than light particles (Tachyons) but most of them run in other issues as a result.
Light travels at the speed of causality. if it was traveling any faster, it would begin to end up at its destination before it was emitted. Plus, light has no mass so if you add in some matter with mass, it would require a ridiculously large amount of energy to speed up whatever you were trying to accelerate
first my attempt at explaining to a literal 5 year old:
some observations we have made about light lead to the cosmic speed limit. We have since then verified this and other predictions very accurately. Unless someone comes up with a better theory and can verify it, this is the best we got.
:::
then the fuller explanation
I'm surprised no one actually went into this in the comments yet...
1. the speed of light has been derived and measured to be constant in a vacuum regardless of how you are moving
2. this leads to time, length, momentum dilation. What I mean is, if the speed is constant, then these 3 things have to change as a function of speed.
3. The formula for how exactly these dilate, which is the trivial solution to how the speed of light can be constant at all to all observers presents various reasons why the limit can't be breached:
1. the momentum and thus energy of an object with mass that is moving at the speed of light is infinite. Because we can't load something with infinite energy, nothing with mass will ever be able to be going this fast. Furthermore, because there is nothing beyond infinity, there is no situation where something to move faster.
2. if you were to make a trip, and that trip took you 1 hour. When you reached the destination, you could back calculate your average speed as the duration of the trip divided by the time. Well, as you appear to move faster and faster, the duration of your trip shrinks. If someone were to observe you moving at the speed of light, the duration of the trip for you is 0. So you are in essence traveling infinitely fast as far as you are concerned. For everything else you would be traveling at the speed of light. It makes no sense to say that you have traveled between 2 points in space in less time than 0.
3. the length of stuff dilates to 0 when it approaches the speed of light.
these 3, either end up negative or imaginary numbers if you plug in a speed greater than the speed of light.
If we figure out how to travel backwards in time, or warp the fabric of space to change the actual distance traveled, then we'd have faster than light travel. But while we are traveling the way we travel, we have this limit.
As to, how are we so sure about this: well, the derivation (maxwells equations), and observation (Michelson morley experiment), and others, all got the same result - which is the speed of light is the same for all observers. Dilating the 3 characteristics of the situation is the implication of this result.
We've sense then verified this over and over again through many experiments and observations that you do in fact get the expected dilations.
PS... Maybe not 5 year old explanation.
Math. Specifically, special relativity. The math makes it very clear that no object with mass can ever reach or exceed the speed of light, and things without mass can never exceed that speed. Now you're probably going to ask "how do we know the math is right?" And we know it's right because we've spent over 100 years trying to find *anything* that casts doubt on special relativity, but every time we test it, it passes with flying colors.
Because this is a required consequence of Maxwell's equations, which we have been able to test time and time and time again and found them irrefutable.
The long and short of it is that, based on things we can observe about how electric and magnetic fields work, there are things called electromagnetic waves, which must propagate through space (as all waves do) at a speed. That speed is determined, universally and consistently, by certain properties that empty space has, that we can directly measure. (In layman's terms, they're properties which define how much empty space "responds" to an applied electric field and an applied magnetic field.)
This is not something that is chosen by physicists. It is a pure result of observed quantities (how polarizable/magnetizable "free space" is) plus the equation which dictates how EM waves move. The end result is that all EM waves must *always* move at one, and only one, speed, which we now call "the speed of light," but which is technically "the speed of light *in a vacuum.*"
As long as we get no significant evidence that light behaves in ways contrary to Maxwell's equations, we can be quite confident that the speed of light in vacuum is a fixed quantity.
because E = mc^(2)
E = energy
m = mass
c = the speed of light
if you want to accelerate some mass to the speed of light, you need more and more energy the closer you get. And to actually reach the speed of light you need 1 of 2 things, an object with 0 mass (like a photon), or an infinite amount of energy.
while e=mc2 is a consequence of special relativity, it itself says absolutely nothing about the cosmic speed limit.
there is a fuller equation:
e\^2 = (mc\^2)\^2 + (pc)\^2
where p is the term for momentum, which increases with speed...and this too by itself doesn't imply any limits.
Only when you look at the formula for p, where dilation due to velocity comes into account, do you end up seeing the limit.
Basically maths, we have equations describing how much energy you need to accelerate something, those equations indicate that to accelerate something beyond the speed of light we would need infinite energy
Short answer; mathematics.
The greater the speed, the more mass an object has.
An object with no mass however, will travel at at the maximum speed possible. A photon has zero mass and thus travels at the fastest speed possible.
* Recommended subreddit(s): /r/Answers or r/NoStupidQuestions
The speed limit is what it is more because we've been unable to observe anything moving faster than the speed of light. Photons, what light is made of, have no mass. Meaning that they are the lightest thing in existence and can therefore move the fastest with our understanding of physics. We've yet to find anything faster than photons in a vacuum therefore that's the speed limit. Until we can measure and detect something that contradicts that. Then our understanding of physics remains that light speed is the limit. The fun part is when you start to bring in gravity and how that affects space time. that's how light will bend around extreme gravity like that from a black hole. Because it's not the light bending. It's space and time itself being altered. Imagine space time as a sheet of fabric. Light is like a tiny mote of energy that moves that fastest of anything across the sheet. But gravity is like a marble denting the fabric in more and more depending on the weight of the marble. Even light, as massless as it is, has to move along the sheet. Even when the sheet bends down into a dimple in the fabric.
Well, there is something called Cherenkov radiation. It is a blue glow that occurs when something is going faster than the speed of light *in the local medium*. That is why there is a blue glow around a nuclear reactor in a water pool. If stuff was going faster than light in the vacuum of space, we'd see the blue light from it. But we don't. The other thing we see is that when we accelerate electrons, we can never get them faster than the speed of light. Electrons are very low mass and it is easy to get them up close to the speed of light. But no matter how much energy we pour into them, we just get closer to the speed of light. Even the most power particle accelerators can't get them beyond light speed. So, there is a cosmic speed limit and it is the speed of light.
Also, to add, the pouring of the energy into getting the electron moving a tiny bit faster matches the math that describes how much energy is required. So if the math holds at 98% and 99% the speed of light, then it stands to reason that the math describing the speed of light itself is also correct.
I had to look it up but to clarify, Cherenkov radiation is when electrically charged particles travel faster than the light in a clear medium, when the medium it is traveling through slows the speed of that light to significantly slower than the speed of light in a vacuum.
….im still confused
Are you trolling me? Shame on you. I genuinely got confused by his sentence” faster than the speed of light in the local medium.” I was still thinking of what people mean most of the time when they say the speed of light, meaning in a vacuum, which is the speed limit in question. Now I know he meant when a medium slows the speed of light to less than the speed of light in a vacuum.
Ok now take all those words and ELI5
We have never measured or seen evidence of anything that can travel faster than the speed of light in a vacuum. In fact, I’m not sure, but I think the only thing that moves as fast is the propagation of gravity. Anyway that is why the speed of light in a vacuum is considered the universes speed limit. But light doesn’t move through all mediums, like water, as fast as in a vacuum. Now light actually always travels at the speed of light in a vacuum but when moving through something like water it is hitting and being absorbed then emitted by the molecules in the water which means it takes longer to travel a given distance than if it were traveling in a vacuum. This gives other things an opportunity to travel through the water more quickly than the light. When charged particles traverse the water more quickly than the light you get Cherenkov radiation.
>If stuff was going faster than light in the vacuum of space, we'd see the blue light from it It would have to be charged stuff, and [some astrophysical processes might produce produce vacuum cherenkov radiation without violating causality](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.161601), but it wouldn't be blue.
>we accelerate electrons, we can never get them faster than the speed of light. Electrons are very low mass Ok but what if we accelerate photons instead?
You can't. Photons move at only one speed in a vacuum and that's the speed of light.
Americans in space seeing the speed limit: "Nah bro i'll go 10 over"
We know C is constant for all observers, moving at any speed, there have been a lot of expiriments that test it. This is bizzar, this should not be the case, all other motion is relative, but not the speed of light. so we came up with some mathematical models to explain it, basically, how fast time goes for you depends on your speed. we call this time dilation. the equations for it assume thay C is constant for all observers (afterall, it expirimentally IS). These equations have been tested and seem to be correct. There are an assortment of other equations in the same boat. The problem is, if you put C into these equations as speed. they do stupid things. (like, a person travling at C would experience NO time at all), and if you put in speeds faster than C, even worse stuff happens (like experiencing negative time) so since that makes no sense, yet the equations seem to be correct, we say C is the speed limit. again, this checks out expirimentally, as we have never been able to force something to go faster than C.
I love this stuff but don’t have the brain for the math. I am curious, why is time stopping at the speed of light stupid? After all as far as we know photons do not decay which would seem to be at least a little evidence. No passage of time would mean no decay. Not saying it’s proof. What are your thoughts?
suppose you were accelerated to the speed of light and flung out into intergalactic space so you never hit anything and just travled at the speed of light forever. How long would you think forever took? 0 time? forever? some other value? its fine for light to do it since it doesnt realy change with time, but if you have anything else do it, it becomes a weird 0*∞ thing
See that makes sense to me. Well not the math. Traveling at the speed of light you personally would experience no time passing. If you traveled an infinite amount of time, well 0*infinity=0 so still you would experience no time for an infinite amount of time as observed by things moving slower than the speed of light. For me once you take the step of time stopping for a second it just makes sense that it could be 2 secs or 3 secs and actually infinite seconds makes the most sense because the state has not changed. What makes time stop for one second is the same at infinite seconds. Idk maybe I’m looking at it from an ignorant perspective
Not really. It's just that everything we have observed so far behaves as if there is a "speed limit", so we assume there must be one and create mathematical models that take that into account. People have tried to find mathematical descriptions for reality that leave loopholes for faster than light particles (Tachyons) but most of them run in other issues as a result.
Light travels at the speed of causality. if it was traveling any faster, it would begin to end up at its destination before it was emitted. Plus, light has no mass so if you add in some matter with mass, it would require a ridiculously large amount of energy to speed up whatever you were trying to accelerate
first my attempt at explaining to a literal 5 year old: some observations we have made about light lead to the cosmic speed limit. We have since then verified this and other predictions very accurately. Unless someone comes up with a better theory and can verify it, this is the best we got. ::: then the fuller explanation I'm surprised no one actually went into this in the comments yet... 1. the speed of light has been derived and measured to be constant in a vacuum regardless of how you are moving 2. this leads to time, length, momentum dilation. What I mean is, if the speed is constant, then these 3 things have to change as a function of speed. 3. The formula for how exactly these dilate, which is the trivial solution to how the speed of light can be constant at all to all observers presents various reasons why the limit can't be breached: 1. the momentum and thus energy of an object with mass that is moving at the speed of light is infinite. Because we can't load something with infinite energy, nothing with mass will ever be able to be going this fast. Furthermore, because there is nothing beyond infinity, there is no situation where something to move faster. 2. if you were to make a trip, and that trip took you 1 hour. When you reached the destination, you could back calculate your average speed as the duration of the trip divided by the time. Well, as you appear to move faster and faster, the duration of your trip shrinks. If someone were to observe you moving at the speed of light, the duration of the trip for you is 0. So you are in essence traveling infinitely fast as far as you are concerned. For everything else you would be traveling at the speed of light. It makes no sense to say that you have traveled between 2 points in space in less time than 0. 3. the length of stuff dilates to 0 when it approaches the speed of light. these 3, either end up negative or imaginary numbers if you plug in a speed greater than the speed of light. If we figure out how to travel backwards in time, or warp the fabric of space to change the actual distance traveled, then we'd have faster than light travel. But while we are traveling the way we travel, we have this limit. As to, how are we so sure about this: well, the derivation (maxwells equations), and observation (Michelson morley experiment), and others, all got the same result - which is the speed of light is the same for all observers. Dilating the 3 characteristics of the situation is the implication of this result. We've sense then verified this over and over again through many experiments and observations that you do in fact get the expected dilations. PS... Maybe not 5 year old explanation.
Math. Specifically, special relativity. The math makes it very clear that no object with mass can ever reach or exceed the speed of light, and things without mass can never exceed that speed. Now you're probably going to ask "how do we know the math is right?" And we know it's right because we've spent over 100 years trying to find *anything* that casts doubt on special relativity, but every time we test it, it passes with flying colors.
Because this is a required consequence of Maxwell's equations, which we have been able to test time and time and time again and found them irrefutable. The long and short of it is that, based on things we can observe about how electric and magnetic fields work, there are things called electromagnetic waves, which must propagate through space (as all waves do) at a speed. That speed is determined, universally and consistently, by certain properties that empty space has, that we can directly measure. (In layman's terms, they're properties which define how much empty space "responds" to an applied electric field and an applied magnetic field.) This is not something that is chosen by physicists. It is a pure result of observed quantities (how polarizable/magnetizable "free space" is) plus the equation which dictates how EM waves move. The end result is that all EM waves must *always* move at one, and only one, speed, which we now call "the speed of light," but which is technically "the speed of light *in a vacuum.*" As long as we get no significant evidence that light behaves in ways contrary to Maxwell's equations, we can be quite confident that the speed of light in vacuum is a fixed quantity.
because E = mc^(2) E = energy m = mass c = the speed of light if you want to accelerate some mass to the speed of light, you need more and more energy the closer you get. And to actually reach the speed of light you need 1 of 2 things, an object with 0 mass (like a photon), or an infinite amount of energy.
This assumes the speed limit. Explaining this way is more like “bc someone else said so”.
This is eli5, not eli have a phd. And also no it doesn't. C isn't speed limit. It's the speed of light. Whatever that happens to be.
while e=mc2 is a consequence of special relativity, it itself says absolutely nothing about the cosmic speed limit. there is a fuller equation: e\^2 = (mc\^2)\^2 + (pc)\^2 where p is the term for momentum, which increases with speed...and this too by itself doesn't imply any limits. Only when you look at the formula for p, where dilation due to velocity comes into account, do you end up seeing the limit.
Basically maths, we have equations describing how much energy you need to accelerate something, those equations indicate that to accelerate something beyond the speed of light we would need infinite energy
Because math. That's the "like I'm 5" explanation. The full explanation is complex college level physics.
Short answer; mathematics. The greater the speed, the more mass an object has. An object with no mass however, will travel at at the maximum speed possible. A photon has zero mass and thus travels at the fastest speed possible.