Altering the speed of light

Nenad

the speed of light would still look like normal. It would still move at a speed of c.

Nenad

SR has been one of the most remarkably accurate theories known to man. It the only theory that works as wee as it does, and giver results that are as accurate as they are.

bino

eventhough im going almost the same speed?

Nenad

yes thats the thing about light, its speed is always c, no matter in waht frame youre in. Even if yuo send two beams of light at each other, the speed at which they approach eachoter is not c+c, it is just c.

bino

so then if we were going the speed of light, light would still be going a lot faster than us?

Doc Al

As has been mentioned several times in this (seemingly endless) thread, one cannot go at the speed of light. So, let's say you were in your rocket going at 0.99c with respect to the earth. Someone (anyone!) fires off a beam of light. Observers on both rocket and earth will measure that beam as traveling at speed c with respect to themselves. The logical consequences of this fact lead to all the SR "effects" that we've been discussing throughout this thread: length contraction, time dilation, and simultaneity.

So, to answer your question directly. Everyone will always measure light as moving at speed c with respect to themselves. So, if that's what you mean by "going a lot faster", then yes. But another observer, watching you go by at say 0.99c, also measures that light as going at speed c with respect to him, so as far as he is concerned the light is only going 0.01c faster than you.

bino

thats interesting.

bino

so you find the length of a moving object by the time*speed?

h8ter

Why is it that when objects only loose length when traveling at relativistic speeds? Well, it is noticeable at relativistic speeds. What actually defines the magnitude of relativistic speed? When do you start applying the Lorentz Transform and why?

In addition to the statement about length contration, I would like to say that length is not PHYSICALLY lost. In one reference frame the length of an object at relativistic speeds is contracted, while relative to that object it is the same. It is not physically lost, because it is contracted and proper in two reference frames. This is contradictory. Nothing can loose length and keep it at the same time. Just my two coins going in.

ArmoSkater87

Since everyday speeds are nothing compared to the speed of light, the length contraction/time dilation/mass increase are neglected. When moving at relativistic speeds (close to the speed of light) these effects are very noticable. For example, mass is a little more than 2 times greater at .9c than the rest mass. Which shows that you have to get very close to the speed of light for the mass to start sky rocketing.

Correct, nothing is physically happening to it, there is no force making it contract. It simply IS shorter at a certain velocity.

Doc Al

As was discussed several posts ago, one way of measuring the length of a moving object is to time how long it takes to pass you, then multiply that time by its speed.

unicorn

And what is your opinion about tachyons, do they exist? Sorry if anyone asked this before.

h8ter

What is the barrier when you start considering speeds relativistic?

How is it simply shorter and at the same time simply the same size as it is when considered at rest to itself?

Tom Mattson

There isn't one. All speeds are relativistic. Now as to the related question, "When do you have to use relativity, and when can you get away with not using it?" the answer is another question: "How accurate do your calculations need to be?"

It is shorter than its proper length according to an observer watching it move by.
It is exactly its proper length in its rest frame.

You have to qualify observational statements with the frame in which the observation is made to make any sense.

h8ter

How can it have two lengths at the same time? Isn't that impossible. I know this is in regards to different inertial reference frames, but reference frames doesn't make something heavier or lighter depending on the speed of one related to another. That would make something have two different masses at the same time.

A good explanation would help me understand.

Tom Mattson

Because it happens to be a feature of the universe we live in that the length of an object is a function of its speed.

No, it isn't. In fact, it's quite impossible for it not to be that way!

The concept of relativistic mass can be accepted or abandoned at will, but we are stuck with length contraction and time dilation. So, I'll be confining my remarks to the latter two phenomena.

It all starts with Maxwell's equations of electrodynamics. This is how Einstein derived Special Relativity from two postulates:

1. The laws of physics must be the same in every inertial frame.
2. The speed of light must be the same in every inertial frame.

The first postulate means that you should not be able to tell whether you are moving or at rest merely by performing an experiment in a closed laboratory. What it really amounts to is that there is no such thing as a state of absolute rest. Equivalently, it means that there is no preferred inertial frame of reference.

The second postulate means that, for any light pulse, its speed will be measured to be 'c', no matter what the relative motion between the source and the observer. So if a source is stationary in your frame and you measure the speed of a pulse, it is 'c'. And if that same source comes at you at 0.5c and you measure the speed of another pulse, you still measure the speed to be 'c' (not 1.5c!).

That second postulate gives an inkling of length contraction and time dilation: Space and time cannot possibly be reckoned the same for all observers, if the speed of light is reckoned the same for all observers.

Now back to Maxwell. What Einstein did was pose the question, "What sort of coordinate transformation would leave Maxwell's equations in the same form for all inertial observers?" This question is relevant because of the first postulate. If the laws of physics have to be the same for everybody, then the equations have to be the same for everybody. Einstein didn't just pose the question, he also answered it: The coordinate transformation is the Lorentz transformation.

And derivable from the LT are the formulas for length contraction and time dilation. So the best way I can think of the "explain" these phenomena is to say that they are deduced from the postulates of SR, which in light of all the experimental data are eminently reasonable, and the covariance of Maxwell's equations, which are well-confirmed experimentally.

h8ter

We are not necessarily stuck with length contraction or time dilation. I've seriously been a firm believer in Einstein's theories, but as of lately, I've kind of trailed off thinking less of what he has theorized.

Time dilation has been tested, and scientist would even say it is proven to exist. I would have to argue that statement. Length contraction has never been observed, nor has mass increase been observed (Not sure about the mass increase, but I'm thinking it hasn't been measured, so dont go too hard on that one).

Would you like to explain to me exactly how light keeps it's constant velocity? I am in accordance with Maxwell saying the frequency is inversly proportional to the wavelength only when the source and detector are stationary. What I do not believe is that this is true when velocity of the source of detector is thrown in. I have no belief that the Lorents Transform did a good job in explaining this phenomenon. So, saying what you just said, has not influenced my thought. Can you go more indepth? I'm going astray; I need to get back on path with physics.