Speed of light - why is it a speed limit?

[AluminumStudios]

I'm sure this is a very old questions asked many times, and quite possibly difficult to explain or understand.

But I've never recieved any kind of explanation as to why you can't travel faster than the speed of light. Everyone has just said "you can't" but never offered me any kind of reasonable explanation ... Can anyone begin to shed some light on this for me (no pun intended.)

 

[Looney]

Because when you approach the speed of light, time slows down for you. And lets just say hypothetically that you have an unlimited amount of energy, the moment you hit the speed of light, time completely stops for you, so you can't get that extra push to go beyond the speed of light.

 

[Pulsar]

Incorrect.

The difficulty is that as your velocity increases, your mass increases proportionately toward infinity.

At the speed of light, you theoretically will have infinite mass. The amount of energy needed to accelerate that mass is infinite as well - i.e., you'll never get there.

There are alot of sites on relativity and the speed of light. Google it and you'll get an answer far superior to any we'll provide.

 

[AluminumStudios]

I guess I'll have to google it, because I want to understand why mass would increase ....

 

[itachi]

c, the speed of light in a vacuum, can and has been exceeded by itself in a different medium.
http://www.nec.co.jp/press/en/0007/1901.html

but like the website says, the findings don't disprove einstein's theory of relativity.


in an open system.. anything that travels at the speed of light has no mass and anything that has mass travels slower than the speed of light. there're dozens of experiments that've been performed to test this.. and has always returned true.
v = c => m = 0
v < c <= m > 0
?

 

[f95toli]

This is just one of those things you can not "understand", only accept.

Now, I don't think it is correct to say it is impossible to reach speeds faster than c *only* because the mass increases. The speed of light,c, is a fundemantal constant and is important in every area of physics; even when the physics has nothing to do with special relativity. One important example that has been discussed here recently is quantum teleportation, no matter what you do you can not transfer information faster than c. So even if you had an infinite amount of energy available (to compensate for the increase in mass) you would not be able to reach speeds>c.

Now, what has this to do with light? Well, it turns out that if you look at physics you will see that in order to be travel at c you need to set m=0 and the only particle which has zero mass is the photon (well sort of, you can't really speak of rest-mass in this case but you get the idea).

That is, light is a limiting case and travels at c because it has no mass; but c is much more than just the speed of light, it is a fundemantal constant just as h or epsilon.

Does that make sense?

 

[Looney]

So time doesn't slow down as you approach closer to the speed of light? I'm not wrong, this is the most common explanation for the laymen... Hawkings and Greene both use this example in their books.

 

[r00tcause]

Originally posted by: Hardcore
So time doesn't slow down as you approach closer to the speed of light? I'm not wrong, this is the most common explanation for the laymen... Hawkings and Greene both use this example in their books.

Well it would, for you.

 

[r00tcause]

Originally posted by: AluminumStudios
I'm sure this is a very old questions asked many times, and quite possibly difficult to explain or understand.

But I've never recieved any kind of explanation as to why you can't travel faster than the speed of light. Everyone has just said "you can't" but never offered me any kind of reasonable explanation ... Can anyone begin to shed some light on this for me (no pun intended.)

You cant get an explanation as to "why mass increases to infinity and time slows down" as you approach the speed of light because *nobody knows*.

Fact: We dont have all the answers.

Just like Gravity. What is it? We done know. We can describe it, just like C, but we cant explain it.

 

[silverpig]

Originally posted by: r00tcause

Originally posted by: AluminumStudios
I'm sure this is a very old questions asked many times, and quite possibly difficult to explain or understand.

But I've never recieved any kind of explanation as to why you can't travel faster than the speed of light. Everyone has just said "you can't" but never offered me any kind of reasonable explanation ... Can anyone begin to shed some light on this for me (no pun intended.)

You cant get an explanation as to "why mass increases to infinity and time slows down" as you approach the speed of light because *nobody knows*.

Fact: We dont have all the answers.

Just like Gravity. What is it? We done know. We can describe it, just like C, but we cant explain it.

Look up some derivations of special relativity. The explanations are there. People know.

For you on the ship, travelling at light speed, you would think time was just normal. You could look at your watch and it would tick away the seconds just like it does on earth.

The lifetime of the universe outside your spaceship would be over in an instant though...

 

[r00tcause]

Originally posted by: silverpig

Originally posted by: r00tcause

Originally posted by: AluminumStudios
I'm sure this is a very old questions asked many times, and quite possibly difficult to explain or understand.

But I've never recieved any kind of explanation as to why you can't travel faster than the speed of light. Everyone has just said "you can't" but never offered me any kind of reasonable explanation ... Can anyone begin to shed some light on this for me (no pun intended.)

You cant get an explanation as to "why mass increases to infinity and time slows down" as you approach the speed of light because *nobody knows*.

Fact: We dont have all the answers.

Just like Gravity. What is it? We done know. We can describe it, just like C, but we cant explain it.

Look up some derivations of special relativity. The explanations are there. People know.

For you on the ship, travelling at light speed, you would think time was just normal. You could look at your watch and it would tick away the seconds just like it does on earth.

The lifetime of the universe outside your spaceship would be over in an instant though...

Ive read countless papers on relativity. You listen poorly. I just said we can describe the properties of C but we cannot explain its reasons. You just described its properties, you did not explain its reasons. Thanks for telling me a bunch fo stuff I already knew.

 

[InseName]

simply put, the newtonian equation only works for slow speeds, for higher speeds refer to einstien's equations.

 

[itachi]

Originally posted by: r00tcause
You cant get an explanation as to "why mass increases to infinity and time slows down" as you approach the speed of light because *nobody knows*.

of course we can.. you just refuse to accept it. read the question in another way and you just might read it as "can someone explain why it's said that.."

Fact: We dont have all the answers.

i'll agree to that.

Just like Gravity. What is it? We done know. We can describe it, just like C, but we cant explain it.

redundant.

Ive read countless papers on relatively. You listen poorly. I just said we can describe the properties of C but we cannot explain its reasons. You just described its properties, you did not explain its reasons. Thanks for telling me a bunch fo stuff I already knew.

countless papers.. and yet, you can't even spell relativity properly.

in einstein's theory of relativity.. momentum is said to be the product of gamma, mass and velocity. gamma is the inverse square root of 1 - (v/c)^2.. when v << c, v/c ~= 0 => gamma ~= 1. the limit as v approaches c is infinity. before you can actually answer why, you have to define gamma.. gamma, the lorentz factor, is a value that comes into factor when length is affected by speed.. the term itself does little to explain "why", it simply just tells you how it is. how the lorentz factor was discovered, blind luck.. why the effect modeled by the lorentz factor is considered to be valid, just a wild guess here.. but maybe, just maybe.. the effect that the lorentz factor models is part of what einstein was explaining? the statement that mass approaches infinity as an objects velocity approaches the speed of light can easily be argued to apply only to people who aren't in that inertial frame of reference.
say a boeing 747 can reach the speed of light and it has an infinite amount of fuel. if the plane flew around in circles around the western hemisphere.. what do you think it would look like? like a huge circle of mass. how would you explain that phenomenon? with einstein's theory of relativity.

and that's what 30 min of reading taught me.. for someone who claims to have read countless papers, you sure do know how to run yourself in circles.

 

[f95toli]

I think that what r00tcause meant was that science can never give an answer to WHY nature behaves in a certain way, it can just tell us HOW it behaves. The reason why we believe SR is correct is because it correctly predicts the outcome of every experiment we have tried so far, not because SR is "natural" or "makes sense" or anything like that.
Most of modern physics is so counter-intuitive that we can never truly understand it, thw world it describes is too different from our low-speed macroscopic world.

 

[itachi]

Originally posted by: f95toli
I think that what r00tcause meant was that science can never give an answer to WHY nature behaves in a certain way, it can just tell us HOW it behaves. The reason why we believe SR is correct is because it correctly predicts the outcome of every experiment we have tried so far, not because SR is "natural" or "makes sense" or anything like that.

yea.. maybe, but aluminum wasn't asking why the phenomenon occurs.. he was just asking for an explanation.
pretty much any question that one can ask.. if asked enough will get to the core nature of the subject. a question of "why" can be answered with an explanation of "how". just because one asks "why" doesn't insinuate that the question is referring to nature.

btw.. who/what's sr?

 

[Sahakiel]

Originally posted by: AluminumStudios
I'm sure this is a very old questions asked many times, and quite possibly difficult to explain or understand.

But I've never recieved any kind of explanation as to why you can't travel faster than the speed of light. Everyone has just said "you can't" but never offered me any kind of reasonable explanation ... Can anyone begin to shed some light on this for me (no pun intended.)

Maxwell's equations.

 

[JAGedlion]

Maxwell gets my vote, dunno how he got them though, never bothered to ask.

 

[silverpig]

Originally posted by: Sahakiel

Originally posted by: AluminumStudios
I'm sure this is a very old questions asked many times, and quite possibly difficult to explain or understand.

But I've never recieved any kind of explanation as to why you can't travel faster than the speed of light. Everyone has just said "you can't" but never offered me any kind of reasonable explanation ... Can anyone begin to shed some light on this for me (no pun intended.)

Maxwell's equations.

Not really. They just allow you to derive the speed of light in a vacuum (or any medium really). That's it.

 

[MoD TaRkIn]

The equation that demonstrates all this is actually quite simple. It links the relativistic mass (ie, the mass you have when you move, becasue when you move you're mass increses.) with the rest mass. This is the mass we are all familiar with, its the mass of an object at rest, although, the rest mass is approximated to be the relatavistic mass of a moving object at less than about 10% c too, simply because they are so close. anyway; m(rel)=m(rest)*gamma. And, gamma is the lorents factor (like itachi said) of 1/sqrt(1-v^2/c^2). This means that as v approaches c, gamma becomes HUGE and will tend to infinity (like everyonw said). Gamma also appears all over the place. It is the factor by which everything changes with speed. Time dilates by a factor 1/gamma, length contracts by gamma etc etc.

Also, it is not beyonde the laws of physics that there exists some exotic form of matter/energy that wouuld allow faster than light travel, it's just really unlikley.

 

[f95toli]

True, but this does not explain WHY there is a maximum speed c, it is merely the mathematical relation that describes what happens when we approach the speed of light.

There is no theory that explains WHY there is maximum speed, SR (special relativity) and ís derived by postulating that the measured speed of light must be the same for all observers regardless of their frame of reference; this is also neccesary in order for Maxwell's equations (which imply a constant speed of light) to be valid for all observers.

 

[imgod2u]

Well, the speed of light was originally calculated using Maxwell's equations of EM. When it was calculated, it was found that it was dependent only on constants and therefore, would remain the same. Needless to say, this was quite upsetting and many explainations was offered. Relativity started from there (that the speed of light would be constant) and from that point, figured out that something else must change (time and space) in order for the speed to be constant despite your point of reference. This came to time and space dialation which produced theories of mass increase and the slowdown of time. Why it happens? Don't know, we only know what we've observed and it happens to imply/match the predictions made by relativity.

 

[kotss]

Originally posted by: MoD TaRkIn
The equation that demonstrates all this is actually quite simple. It links the relativistic mass (ie, the mass you have when you move, becasue when you move you're mass increses.) with the rest mass. This is the mass we are all familiar with, its the mass of an object at rest, although, the rest mass is approximated to be the relatavistic mass of a moving object at less than about 10% c too, simply because they are so close. anyway; m(rel)=m(rest)*gamma. And, gamma is the lorents factor (like itachi said) of 1/sqrt(1-v^2/c^2). This means that as v approaches c, gamma becomes HUGE and will tend to infinity (like everyonw said). Gamma also appears all over the place. It is the factor by which everything changes with speed. Time dilates by a factor 1/gamma, length contracts by gamma etc etc.

Also, it is not beyonde the laws of physics that there exists some exotic form of matter/energy that wouuld allow faster than light travel, it's just really unlikley.

Actually, you have stated the situation improperly. It is M(rel) = m(rest)/gamma.

When V approaches C. The v^2/c^2 becomes closer to 1 and 1 - 1 becomes zero.
When 1-V^2/C2 becomes zero you will take the square root of zero which is zero, then you will have
division by zero which results in infinity.

As to why c is a speed limit, no one can actually tell you why. Can only give you explanations as to why
it is believed to be a limit for objects that have rest mass. Why it is the speed that it is or why properties
of matter truly act the way they do, the answer is truly unknown. We can use Gravity to our advantage
or disadvantage but we do not actually know what makes it work, only that it works as we expect it
too. I believe the same this holds as to the speed of light. It is what it is. I am brushing up on my physics
to delve deeper into these topics that fascinate me so. I accept it for now. Sometimes there are truths
that we just have to accept. Does not mean we will not understand at some later time, but based on
our current technical level that is all we have.

 

[aplefka]

I've got a question somewhat related to this. If you travelled, let's say, one lightyear, is there any way to measure how much time would have passed on earth? Because if time works differently at the speed of light, one year travelling at that speed would be different than just 365 days would it not?

 

[Jeffyboy]

It's the only readily available radiation that can be easily reproduced and aligned and measured so... we call it a limit ;-) We could say tachyons are faster but, that's still a theoretical particle. It's all mathemetics up to this point. All formulas are subject to revision as you discover new and wonderful things about this universe.

Jeff

 

[r00tcause]

Originally posted by: itachi

Originally posted by: r00tcause
You cant get an explanation as to "why mass increases to infinity and time slows down" as you approach the speed of light because *nobody knows*.

of course we can.. you just refuse to accept it. read the question in another way and you just might read it as "can someone explain why it's said that.."

Refuse to accept it? I will agree that i was answering a question not yet asked. The answer is "because mass increases to infinity and it would take infinite energy". Thats a very incomplete answer. Ok so then, what is causing the "resistance" to super-luminal speeds?

countless papers.. and yet, you can't even spell relativity properly.

The response of a 2 year old. I was typing quickly and didnt notice I mistyped. I fixed it.

in einstein's theory of relativity.. momentum is said to be the product of gamma, mass and velocity. gamma is the inverse square root of 1 - (v/c)^2.. when v << c, v/c ~= 0 => gamma ~= 1. the limit as v approaches c is infinity. before you can actually answer why, you have to define gamma.. gamma, the lorentz factor, is a value that comes into factor when length is affected by speed.. the term itself does little to explain "why", it simply just tells you how it is. how the lorentz factor was discovered, blind luck.. why the effect modeled by the lorentz factor is considered to be valid, just a wild guess here.. but maybe, just maybe.. the effect that the lorentz factor models is part of what einstein was explaining? the statement that mass approaches infinity as an objects velocity approaches the speed of light can easily be argued to apply only to people who aren't in that inertial frame of reference.
say a boeing 747 can reach the speed of light and it has an infinite amount of fuel. if the plane flew around in circles around the western hemisphere.. what do you think it would look like? like a huge circle of mass. how would you explain that phenomenon? with einstein's theory of relativity.

and that's what 30 min of reading taught me.. for someone who claims to have read countless papers, you sure do know how to run yourself in circles.

Asbolutely none of that is relevant to what I was saying. Interesting, but irrelevant. If your above speculation were accurate, then you are implying that super-luminal speed only "appears" to require infinite energy and that in fact the entire principle of light being a speed barrier is false.

How can I make 1 post and "run myself in circles"? Thats interesting in itself!