# B What Einstein said on faster than light travel

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1. Oct 3, 2016

Hi, I'm a CAD student, writing a research paper for my English Comp. class on interstellar travel. I wan't to quote Einstein but can't find were he stated this exactly: Because space and time are relative, the faster you move through space the slower you move through time relative to someone who is stationary and as you move faster and faster you also gain more and more mass requiring more and more energy to accelerate, so that you would never be able to gain enough energy to move something as fast as something with no mass, such as light. Also, if you theoretically could reach the speed of light, time would completely stop for you and if you were to go faster than the speed of light, then time would actually start to go in reverse and you would travel backwards in time. Can someone point it out for me in his paper please, or find a quote otherwise? https://www.fourmilab.ch/etexts/einstein/specrel/www/

Thank you

2. Oct 3, 2016

### Staff: Mentor

That's because he didn't, at least not anywhere I'm aware of, since not all of it is correct and some of it, while not exactly wrong, is not stated very well.

This is not a good way to think of time dilation, because "moving through time" implies that "time" is something absolute, and it isn't.

Theoretically you can't reach the speed of light, or exceed it, so this is not correct. Starting with an assumption that is inconsistent with a theory is not a good way to explore what the theory actually says.

3. Oct 4, 2016

### Ibix

The simplest answer to your question, @EricjamesCADstudent, is to look at the two postulates, labelled 1 and 2 at the beginning of the section titled "On the Relativity of Lengths and Times". Accelerate a bit. You instantaneously match speeds with someone who isn't accelerating, who can consider themself to be stationary. Repeat. What does the second postulate tell you?

4. Oct 4, 2016

Okay, I'm trying to explain why you can't reach the speed of light in my paper. Do you have a suggestion as to what and whom I should quote?
Also, do you believe that warp drive is possible?

5. Oct 4, 2016

### Ibix

See #6 (edit: there seems to have been some mentor activity - #6 is now #3) above.
It requires negative mass ("exotic") matter. We have never seen such a thing and have no real reason to believe it exists. So the whole thing is impossible forthe forseeable future, and probably forever, sadly.

Last edited: Oct 4, 2016
6. Oct 4, 2016

### Prem1998

I agree. After you said the thing about imaginary numbers, I've changed my thought. Now, I think we can consider speeds greater than light in the theory and get some meaning out of the consequences. But not here. That's not the topic of this thread.

7. Oct 4, 2016

### Staff: Mentor

You don't really need to quote anyone. The fact that no ordinary object with nonzero rest mass can reach the speed of light is such a basic prediction of SR, and has been verified experimentally so many times, that you can just state it as a fact.

8. Oct 4, 2016

### Chronos

If it is possible to synthesize exotic matter, warp drive is a possibility. I suspect, however, the process required for synthesis would be far beyond the reach of any currently known technology and an engineering nightmare.

9. Oct 4, 2016

### Mister T

The speed of light is the same for all observers. Thus, if you chase after a light beam it will forever recede from you at that same speed regardless of how fast you pursue it. It is thus not possible for you to reach that speed, let alone surpass it. Google "Einstein's Second Postulate".

If I'm guessing your purpose correctly, it's not needed. If you head towards a distant location, the distance to that location contracts. The closer you get to the speed of light, the shorter the distance. Thus, by travelling fast enough you can make it to a location, say 100 light years away, in just a few minutes. Or even less. You can make the distance as arbitrarily close to zero as you like, depending on how fast you travel.

Keep in mind, though, that back home at least 100 years will pass during your journey, even though only a few seconds may elapse on your space ship.

Of course the practical limitations of doing this are tremendous, but theoretically it's possible.

Gene Roddenberry claimed that he used a warp drive in Star Trek because the facts of relativity would be too complicated (for his story lines).