# Why can't light travel faster than c?

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rootone
C is what it is
Many experiments confirm this.
It could be another number. but it isn't; it's what it is

Why is it that number and not something different?. is not some thing that science can address,.
You could ask why is PI the number that it is

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C is what it is
Many experiments confirm this.
It could be another number. but it isn't; it's what it is

Why is it that number and not something different?. is not some thing that science can address,.
You could ask why is PI the number that it is
Why pi is what it is is more fundamental. You could ask an alien civilisation and they would, once they understood what you were asking, give you the same number. The speed of light is chosen by us through our definition of the units we use.

Mentor
C is what it is Many experiments confirm this. It could be another number. but it isn't; it's what it is Why is it that number and not something different?. is not some thing that science can address,. You could ask why is PI the number that it is

The exact value of c depends on units used. It's really is not relevant to fundamental questions - although very important to applied mathematicians or physicists, engineers and such in practical applications. I explained one way to see its constant in all frames by showing it leads to magnetic fields. The second reason given is perhaps easier - according to Maxwell's equations its speed does not depend on the speed of the source.

Thanks
Bill

Eric Bretschneider
For what the same reason you can’t outrun yourself.

Seriously? Why can’t Light travel faster than light? Nothing travels faster than itself.

Sorcerer
Photons do not have mass, so why stop at 299700 km/s??
That’s just a number. There are units where c is just the number 1. There is a universal speed limit. It is either infinite or finite (Lorentz transformation). Experiment conforms the latter. It doesn’t matter what particular number you call that speed. Whatever it is, it is the maximim speed.

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For what the same reason you can’t outrun yourself.

Seriously? Why can’t Light travel faster than light? Nothing travels faster than itself.

Light is unique in that it has an invariant speed in all inertial reference frames (IRF).

A massive object, like you, for example will have a different speed in different reference frames.

If you are at rest in one IRF and emit a pulse of light, you measure its speed as ##c##.

In another IRF, moving with respect to the first, you will have some speed ##v##, but the light pulse will still have a speed of ##c##.

That does require an explanation.

Eric Bretschneider
Light is unique in that it has an invariant speed in all inertial reference frames (IRF).

A massive object, like you, for example will have a different speed in different reference frames.

If you are at rest in one IRF and emit a pulse of light, you measure its speed as ##c##.

In another IRF, moving with respect to the first, you will have some speed ##v##, but the light pulse will still have a speed of ##c##.

That does require an explanation.

You are still ignoring the core concept of the question. There is a logical answer that doesn’t require any physics. Replace “light” with “a horse”. Remember the c is the speed of light meaning the transformed question becomes: “why can’t a horse travel faster than the speed of a horse?”

There is no need to delve into discussions that the speed of light is constant and that it can’t travel slower or faster.

Step back and see the Forrest and not the trees.

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You are still ignoring the core concept of the question. There is a logical answer that doesn’t require any physics. Replace “light” with “a horse”. Remember the c is the speed of light meaning the transformed question becomes: “why can’t a horse travel faster than the speed of a horse?”
.

There is no "speed of a horse". There is a thing called a "horse race", where horses run against each other and the fastest horse wins.

A light race, on the other hand, would be a bit of a non event.

PS more scientifically, there is, for example, no such thing as the speed of an electron, although all electrons are identical.

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Replace “light” with “a horse”. Remember the c is the speed of light meaning the transformed question becomes: “why can’t a horse travel faster than the speed of a horse?”
You are correct that you can play word games here. Alternatively we could discuss physics.

Why does a horse not travel faster than 30mph (or whatever its top speed is) has an answer in terms of its muscles' power output and its joint structure. It's not unreasonable to wonder if there isn't a similar answer for why light travels at 3x108m/s. There isn't, really, although you can spin the question off in many interesting directions.

bhobba
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Why does a horse not travel faster than 30mph (or whatever its top speed is) ...

It will travel faster if you put it in a horse box and drive it along the motorway

Mentor
There is no need to delve into discussions that the speed of light is constant and that it can’t travel slower or faster..

Light has the strange property of being the same speed regardless of the speed of the source. Horses do not have that quirky characteristic ie if they run at 20mph on a 30mph train carriage they will be running at 50mph

Why is light so strange - well we have Maxwell's equations - but if that explains it or simply say's the same thing in a more detailed way is an interesting question (you simply notice the speed of the source is not part of the solution for EM radiation and its speed) - but more for philosophy than physics.

Another possibility is the thought experiment Einstein asked. Heuristically light waves are created because a changing electric field creates a changing magnetic field which creates a changing electric field and so on, propagating at the speed of light. Now let's get on a bike and travel at the speed of light - then the fields will not be changing - but light can only exist if they are. The solution is it travels at the same speed regardless of the speed of the bike.

Thanks
Bill

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Helios
There's also the universal speed of a stationary particle. They say you can't get any slower than that.

Eric Bretschneider
Eric Bretschneider
You’re still missing the point. The question is why can’t Light travel faster than the speed of light?

Stop thinking like a physicist because anyone who asks the question has no physics background. My response is an effort to make the originator of the thread to stop and think about what they asked so that they can ask a better question.

Why can’t something travel faster than itself? It’s a ridiculous question. Why is the speed of light constant? Would be vastly better

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There's also the universal speed of a stationary particle. They say you can't get any slower than that.
That is a nonsensical statement. There is no such thing as a stationary particle in the kind of absolute terms you clearly intend.

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You’re still missing the point. The question is why can’t Light travel faster than the speed of light?
That is indeed the thread title, and if that were the question it would be subject to the criticism that you're directing at it. However, the body of the original post seems to clarify that the original poster is using ##c## to represent the quantity 299700 km/sec, so the question being asked is "Why that particular speed, and what limits the speed of light to that value?"

bhobba, PeroK and Ibix
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Why can’t something travel faster than itself? It’s a ridiculous question.

You supposedly have a PhD in Chemical Engineering. You should know better. The question is why can't light travel faster than C. C is the invariant speed that comes from the derivation of the Lorentz transformations I gave using group theory. The question is not why light can't travel faster than itself - the question is why can't light travel faster than the invariant speed C, which is by definition the constant velocity the same in all frames that naturally emerges in deriving the Lorentz transformations. It can't travel faster than that invariant speed because as you travel faster and faster you never catch up to it due to its invariance. Another way of looking at it is C, by definition, is the speed of light in a vacuum from a stationary source. Normal velocities go faster if their source goes faster - light does not and that's why light or anything else can't go faster than C. Its a perfectly valid question - but for some reason you chose to think its not valid. With your educational background how you made such as error beats me.

The question to ask is why is that invariant speed the speed of light. Symmetry considerations prove such a speed exists, that it is the speed of light is the follow up question which this thread has tried to answer.

Thanks
Bill

PeterDonis
Eric Bretschneider
Who cares about language any more - is communication becoming a lost art because everyone tries to guess at the meaning and intent of the question?

A detailed answer to a poor question really doesn’t do anything for the person asking the question. Giving the simple answer may force them to think about their question and perhaps ask a much better question.

Consider it a version of the Socratic method of teaching with the difference that instead of asking a question, I was attempting to force someone to think more before asking a question.

To each his own. Sorry, but I have had to teach and train individuals throughout my career and forcing someone to think rather than giving a detailed answer that is well above the apparent technical level of the person who asked the question doesn’t work well.

There are some great technical answers on this thread - I DO NOT QUESTION THAT THEY ARE VALID, but if someone understood those answers they never would have asked the question in the first place.

Lorentz transformations using group theory to answer a very simple question about the speed of light? If you know Lorentz transformations you almost certainly know the speed of light is constant.

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This thread has run its course. It is closed.