Why is the speed of light a limit?

[peachoftree]

Say I was moving in a rocket traveling at c, and I do a 1 m/s burn. What stops me from traveling at c + 1m/s?

[Brethern]

Something to do with that 1m/s burn requiring infinite fuel because the ship has infinite weight.

[arkie87]

Something to do with that 1m/s burn requiring infinite fuel because the ship has infinite weight.

that's one way of looking at it.

another way is that time itself slows down such that velocity, which is distance divided by time, cannot increase because time (which is in the denominator) increases too fast at speeds near that of light

if that made sense, great! if not, dont worry about it...

[Kerbart]

As Brethern pointed out, your mass increases with your velocity. At light speed, your mass would be infinite, and since acceleration is proportional to force divided by mass, your acceleration would be zero, regardless of how powerful your engine is.

[peachoftree]

ok. I can understand why the speed of light is a limit if mass increases with velocity, but why does mass increase with velocity?

[SargeRho]

Because you have more energy the faster you move, and energy and mass are the same thing. Near the speed of light, your mass increases in such an extreme manner that you have to spend infinite energy to accelerate to the speed of light - this is heavily simplefied of course.

Also If you have no rest mass, you can not move at any speed other than the speed of light.

[xrayfishx]

ok. I can understand why the speed of light is a limit if mass increases with velocity, but why does mass increase with velocity?

Nobel prize to the one who answers that. I'm sure someone is going to post some shiny math to show you, but why the universe actually works like that, who knows?

Edit: Ninjad.

[arkie87]

ok. I can understand why the speed of light is a limit if mass increases with velocity, but why does mass increase with velocity?

E = m c^2

Energy is mass and mass is energy.

If you are moving fast, you have kinetic energy, so, you have additional mass.

This is also the reason that some elementary particles are said to have zero "rest mass", but have (inertial) mass, since they are moving and have kinetic energy

[Tex_NL]

To get a decent answer to your question you should talk to a theoretical physicist. And even then it would take a good deal of maths, relativity and quantum mechanics to explain it all.

It's a lot easier to just accept it as the ultimate speed limit. But as much as it is a limit that can't be broken it might be possible to avoid it. Hyperspace, warp speed, wormholes, etc.

[K^2]

Something to do with that 1m/s burn requiring infinite fuel because the ship has infinite weight.

But you have infinite weight of fuel to work with, which, by the way, carries infinite amount of energy.

External frame is bad for understanding this. Thing is, from perspective of the ship, you can allways add another 1m/s. The problem is that it doesn't make objects around you move 1m/s faster. This has to do with the way relativistic velocities are added.

[Newt]

If I get the question right, it is not asking about the symptoms, of increasing mass, or nonavailability of infinite energy, rather about really why. Why does the mass increase with the velocity of an object? Why does the Universe pay so much heed to that one speed?

I agree that there is a possibility of getting very deep into this, and trying to evaluate why with fancy maths and theoretical physics, but the real answer for now is probably best that no one knows. We have evidence that it does this, it makes sense based on many experiments, based on much observational evidence, but ultimately it is yet unanswered.

Then again, you can also maybe be satisfied by the idea of multiple reference frames. You can go faster, and a ship that fires its engines, launching from another ship will be going clearly slightly faster to both parties involved, the one at .9999999c, and the one at .9999998c. Time will just be going differently for the two vehicles, and for the people watching from a nearby star system, making it look to each, as though relative to them, c is constant.

[Ikaneko]

No objects with mass can travel at the speed of light or faster. Light photons *technically* have no mass, which is how they can travel at the speed of light.

[DerpenWolf]

If mass increases with velocity then does the gravitational pull of that object increase as well?

[*Aqua*]

Of course!

...

That's an interesting question! Infinite mass also means infinite gravity. So mass moving with lightspeed would end our universe by ripping all of spacetime in pieces!

Edited December 11, 2014 by *Aqua*
typo

[1of6Billion]

Things would be more fun if it where the other way around. Infinite speed with limited mass

[vexx32]

Okay, so this all boils down to one very basic, experimentally verified fact: the speed of light in a vacuum, c, is a constant in all reference frames. This essentially means that no matter how fast you're moving relative to anything else, if you measure the speed of light you will always get c.

Einstein's Theory of Relativity (I always get General and Special Relativity messed up, because I don't know much more than the basics myself) was developed in an attempt to explain this phenomenon. He concluded that in order for that result (c being a universal constant regardless of inertial frame of reference) to be possible, time must dilate as you approach c, and space must contract along the axis of travel (the direction you happen to be moving) as you approach c. In addition, mass dilates as well. Because of these, although the surrounding universe would eventually look extremely odd (an observer travelling near c would view the surrounding, slow-moving universe as very, very thin), it is impossible to reach c.

As to exactly why this occurs... well, it's a question on par with 'why is gravity an attractive force?' and 'why don't we see the effect of quantum fluctuations?'. We just don't know why the laws of physics in our universe are as we have observed them to be. Our models allow us to understand it better, but they are most likely quite far from perfect and will see a great deal of refinement in the centuries to come, opening up new avenues to explore as they are continually improved upon.

[Guest]

We have evidence that it does this, it makes sense based on many experiments, based on much observational evidence, but ultimately it is yet unanswered.

I did a quick google search for "evidence that mass increases with velocity" and turned up a bunch of though experiments and mathematical proofs, but no actual physical experiments that show mass increasing with velocity. Do you have a link to any experiments or observations that show physical mass increasing with velocity? I'd be interested in studying this more. It looks to me like this theory is nothing more than an attempt to explain away "magical" things that happen in particle colliders and such. Things that defy logical explanation. Things that our feeble minds fail to comprehend just yet. I'm sure that I don't have to bring up the fact that at one time everyone knew the world was flat. Oh, wait a minute, the world isn't flat. Well, everyone knows that you can't go faster than the speed of sound. Oh, wait a minute......

[N_las]

I did a quick google search for "evidence that mass increases with velocity" and turned up a bunch of though experiments and mathematical proofs, but no actual physical experiments that show mass increasing with velocity. Do you have a link to any experiments or observations that show physical mass increasing with velocity? I'd be interested in studying this more. It looks to me like this theory is nothing more than an attempt to explain away "magical" things that happen in particle colliders and such. Things that defy logical explanation. Things that our feeble minds fail to comprehend just yet. I'm sure that I don't have to bring up the fact that at one time everyone knew the world was flat. Oh, wait a minute, the world isn't flat. Well, everyone knows that you can't go faster than the speed of sound. Oh, wait a minute......

"... "magical" things that happen in particle colliders and such. Things that defy logical explanation."

Those "magical" things actually have logical explanations. And some of these "magical" things are the evidence you are asking for.

" I'm sure that I don't have to bring up the fact that at one time everyone knew the world was flat."

When was that time? And who thought that? As far as I know, every educated person in the last 2500 years knew the earth is round. The moment we could do experiments on the earths roundness (the greecs did it with shadows and sticks), we knew the earth was round.

"Well, everyone knows that you can't go faster than the speed of sound."

Who in history has ever claimed that moving faster than the speed of sound is impossible? We had bullets moving at supersonic speeds for hundreds of years. Just because some people believed it to be unlikely that supersonic airplanes are possible doesn't mean anything.

Next your are claiming that according to physics the bumblebee can't fly... You seem to be a walking textbook of science-history-misconceptions.

Edit:

And a quick google search didn't show anything? Wow... You really are a master of investigation!

http://en.wikipedia.org/wiki/Kaufmann%E2%80%93Bucherer%E2%80%93Neumann_experiments

http://scholarship.rice.edu/handle/1911/18426

http://adsabs.harvard.edu/abs/1964AmJPh..32..551B

http://arxiv.org/abs/1108.5977

http://adsabs.harvard.edu/abs/2005JPhB...38S.741P

Edited December 11, 2014 by N_las

[theend3r]

Okay, so this all boils down to one very basic, experimentally verified fact: the speed of light in a vacuum, c, is a constant in all reference frames. This essentially means that no matter how fast you're moving relative to anything else, if you measure the speed of light you will always get c.

I know this isn't right but I do not know why so I would appreciate if someone enlightened me:

If you theoretically moved at the speed of light (I know it's impossible ofc), wouldn't the relative speed of light with the same direction vector be 0? Wouldn't the light move alongside you?

Actually wouldn't all the light have a "speed" of 0 in your reference frame since the time around you would essentially stop?

[N_las]

I know this isn't right but I do not know why so I would appreciate if someone enlightened me:

If you theoretically moved at the speed of light (I know it's impossible ofc), wouldn't the relative speed of light with the same direction vector be 0? Wouldn't the light move alongside you?

Actually wouldn't all the light have a "speed" of 0 in your reference frame since the time around you would essentially stop?

Moving at c is so impossible, that you can't even "theoretically move" at the speed of light. So there are no anwers to your questions.

Travelling to the moon was impossible for Galileo Galilei. But only because of practical reason. So he could ask: "If we theoretically moved to the moon, what would happen".

But this question is only valid, because it is theoretically possible to go to the moon.

Omnipotence is impossible to obtain. If we could aks: "If theoretically we were omnipotent, could we create a rock so heavy that we coudn't lift it?"

This question is invalid, because it is even theoretically impossible to be omnipotent.

Edited December 11, 2014 by N_las

[Newt]

Actually wouldn't all the light have a "speed" of 0 in your reference frame since the time around you would essentially stop?

Well, no. Time from the perspective of a moving object constantly adjusts itself such that the speed of light relative to that moving object is constant. Though it is impossible, a hypothetical spacecraft (or bouncy ball ), moving at the speed of light, would perceive time to stop. This would mean that between the bouncy ball and a hypothetical photon near by it (or on the other side of the universe), there would be no increase or decrease in distance at all. But that would have to be taken with the understanding that no time has elapsed for the bouncy ball, so the distance (0m) divided by the time (0s) really does not go at all against that limit of velocity, as velocity's measurement mandates the passage of time. You could do the same evaluation for me sitting at my computer. If time were to freeze, the distance between myself and any photon would remain constant and static.

@Otis: N_Las provided a few good sources for you. You have to remember for this, that we routinely accelerate particles to nearly the speed of light in particle accelerators.

@Derpen Wolf: That is an interesting thought. I am thinking it might have something to do with the time dilation, and an apparent mass change not a physical one. But I am thinking about it, and would be curious for any other ideas.

Edited December 11, 2014 by Newt

[Mr Shifty]

If you theoretically moved at the speed of light (I know it's impossible ofc), wouldn't the relative speed of light with the same direction vector be 0? Wouldn't the light move alongside you?

Actually wouldn't all the light have a "speed" of 0 in your reference frame since the time around you would essentially stop?

Relativity doesn't work at light speed. You could try to do a thought experiment to figure out what a photon "sees", but you can't use the equations of relativity to figure it out; you get infinities in your ratios and the equations become unsolvable. You run into problems with how the photon could exist in the first place.

It's maybe better to ask what happens as you approach light speed. The main effect that you'd experience subjectively is Lorentz contraction: that is, the distance to all objects in the direction of your travel would shrink. Lorentz length contraction sort of maps time dilation into and out of your subjective frame. It's how you could reach a galaxy that's 160,000 light years away in 40 subjective years. It's not that you're going faster than light speed; it's that the galaxy gets closer to you.

In a universe that contained nothing but you and your vessel, there would be no way to tell what speed you're travelling. You could always accelerate, and detect the results of the acceleration, but without some external reference, you can't measure your velocity. That's what relativity means. Think about it for a minute. According to classical mechanics, you'd suppose that if you started at rest and accelerated at 10 m/s², that you'd reach light speed in 30 million seconds (about a year.) If you sent out a light pulse ahead of you before you started accelerating, you should match its speed after a year, then be able to catch up to it. But you won't. In fact, if you could detect it (say, through a system of relays that send a signal to you when your light pulse passes them), you'd notice that it's still travelling away from you at light speed. No matter how much you accelerate, it's still receding at light speed. (Note: You'd measure the same thing if you hadn't accelerated at all. The light pulse would travel away from you at light speed. In fact, if you accelerated directly away from the direction of the light pulse, you'd again measure the same thing. And reconciling that seeming paradox is one way to derive all the equations of special relativity.)

It's impossible to catch-up to or match speeds with light. You can only measure your speed relative to an external reference frame (like, for instance, the visible universe.)

Edited December 11, 2014 by Mr Shifty

[John FX]

Say I was moving in a rocket traveling at c, and I do a 1 m/s burn. What stops me from traveling at c + 1m/s?

Exactly the same as if you have an infinite number of monkeys and they breed, doubling the number.

You`d still only have an infinite amount of monkeys.

What is stopping you having twice as many monkeys? The fact you already have as many monkeys as you possibly can...

It`s sort of the same. The question does not make sense in the real universe.

Tachyons (if they exist) may argue the point but they can`t go as slow as the speed of light for similar reasons.

EDIT :

Relativity doesn't work at light speed. You could try to do a thought experiment to figure out what a photon "sees", but you can't use the equations of relativity to figure it out; you get infinities in your ratios and the equations become unsolvable. You run into problems with how the photon could exist in the first place.

It's maybe better to ask what happens as you approach light speed. The main effect that you'd experience subjectively is Lorentz contraction: that is, the distance to all objects in the direction of your travel would shrink. Lorentz length contraction sort of maps time dilation into and out of your subjective frame. It's how you could reach a galaxy that's 160,000 light years away in 40 subjective years. It's not that you're going faster than light speed; it's that the galaxy gets closer to you.

In a universe that contained nothing but you and your vessel, there would be no way to tell what speed you're travelling. You could always accelerate, and detect the results of the acceleration, but without some external reference, you can't measure your velocity. That's what relativity means. Think about it for a minute. According to classical mechanics, you'd suppose that if you started at rest and accelerated at 10 m/s², that you'd reach light speed in 30 million seconds (about a year.) If you sent out a light pulse ahead of you before you started accelerating, you should match its speed after a year, then be able to catch up to it. But you won't. In fact, if you could detect it (say, through a system of relays that send a signal to you when your light pulse passes them), you'd notice that it's still travelling away from you at light speed. No matter how much you accelerate, it's still receding at light speed. (Note: You'd measure the same thing if you hadn't accelerated at all. The light pulse would travel away from you at light speed. In fact, if you accelerated directly away from the direction of the light pulse, you'd again measure the same thing. And reconciling that seeming paradox is one way to derive all the equations of special relativity.)

It's impossible to catch-up to or match speeds with light. You can only measure your speed relative to an external reference frame (like, for instance, the visible universe.)

This relates to a question I asked in the science lounge about a single subatomic particle far far far into the future when expansion has moved all other matter so far away that light (or other forces) can never affect it again.

My point was that if there is a delay caused by the speed of light, eventually stuff moves so far apart that even the speed of light is not enough to allow an effect to transfer due to universal expansion, it`s why we will just see a dark sky with no stars eventually from this point in space.

It`s at that point when *all* other matter is too far away to affect the subatomic particle, even if the force travels at the speed of light, that is the point I am talking about.

Also, when stuff moves fast, time goes faster meaning if you go at the speed of light then you would instantly find yourself at the end of time because of time dilation. This implies that if you can COMPLETELY stop, you would experience no time. Subatomic particles move relative to each other and so give an internal frame of reference for macro objects. If you remove that, what could they use as a frame of reference?

When all matter is so far away that it does not affect the particle, what gives it a frame of reference?

Edited December 11, 2014 by John FX

[Camacha]

Say I was moving in a rocket traveling at c, and I do a 1 m/s burn. What stops me from traveling at c + 1m/s?

Isn't this the car at 1c turning on its headlights all over again? I think this question has been answered a couple of times on this forum, with a number of very nice and comprehensive posts. I'll see if I can dig some up for you.

[Guest]

I cannot remember exactly - I got my university degree very long time ago.

As far as my failing memory tells me, universe needs maximum speed limit to avoid some funny things with causality - like time travel, knowing something happened before it happened, and such. Since photons have zero rest mass, they move at max speed. Why max speed = C ? Speed units based on length units and time units, and time units are arbitrary, so C as well might be equal to 1.

Edited December 11, 2014 by Guest
Damn so many typos.