# Einstein and idea that nothing can travel faster than the speed of light

1. Dec 3, 2009

### cyberfish99

I was reading about Eisteins theories and had a question. If light can not escape the gravitational pull of a black hole, then assuming that the black hole accelerates (at a constant acceleration) all matter and energy into its event horizon, then if the gravitational pull overcomes the speed of light, anything that enters the event horizon is accelerated to a speed faster than the speed of light. I would just like to know if I am onto something or if this idea has already been posed. I understand that tachyons go faster than the speed of light. Please let me know if anything in this post is completely off basis.

2. Dec 3, 2009

### DaveC426913

This assumption is incorrect. As any object approaches relativistic speeds, its velocity is calculated using a non-linear formula - the Lorentz transformation.

$$\gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}}$$

Last edited: Dec 3, 2009
3. Dec 3, 2009

### cyberfish99

Could you just explain the Lorentz Transformation a little better, I am not sure what it is.

4. Dec 3, 2009

### Staff: Mentor

Tachyons are completely hypothetical, they have never been observed.

5. Dec 3, 2009

### Phyisab****

Yep you are gonna revolutionize physics with this half baked idea. Maybe you should learn some math before you start believing that you are "onto something".

6. Dec 3, 2009

### cyberfish99

Yes while this is true, tachyons are theorized to release Vavilov–Cherenkov radiation which we know about. Like black holes, while we can't actually see them, we can postualize where they are by their interactions with observable phenomina

7. Dec 3, 2009

### Staff: Mentor

Please cite a peer-reviewed source for the claim that anyone has purported to have detected tachyons by their Vavilov-Cherenkov radiation.

8. Dec 3, 2009

### cyberfish99

Last edited by a moderator: Apr 24, 2017
9. Dec 3, 2009

### Danger

Between my fatigue level and watching Family Feud, I managed to read only the first couple of pages of that. I cannot, therefore, comment upon the scientific accuracy. It definitely is not a peer-reviewed publication, though.

10. Dec 3, 2009

### Staff: Mentor

I asked for a peer-reviewed source. If you cannot provide such then you are in violation of the PF guidelines which you agreed to when you signed up for your account. Please re-read the "Rules" link at the top of each page.

Also, from the pages I could see there was not even any non-peer-reviewed evidence provided supporting the experimental confirmation of tachyons, merely a description of what they could be like theoretically and how they might possibly be detected experimentally. There is a large difference between saying how something could be detected and saying that it has been detected.

Last edited: Dec 3, 2009
11. Dec 3, 2009

### DaveC426913

The poster has done some reading and has asked some questions, even going as far as asking where his thinking is off.

There is no call for sarcasm or for put-downs.

(Please note that this exchange occurred in posts 1-4, prior to any speculative discussion about Vavilov-Cherenkov radiation.)

12. Dec 3, 2009

### cyberfish99

Well no need to snippy. I am new to this physics forum and just wanted to know if something that I had postulated had any leg to stand on. As for the peer-reviewed article, I am sorry I came prepared to a fight with only a derringer when I obviously needed a nuclear warhead. You can easily turn people off to the idea of physics just by doing things like that. Instead of biting their head off, how about giving them irrefutable evidence that their idea is wrong. I just posed a question, I didn't want this to turn into some giant debate.

13. Dec 3, 2009

### sophiecentaur

Now now boys.
Stop squabbling.

If we got cross at every ill thought out idea where would we be?
Let him that is without sin cast the first stone. (Ducks)

14. Dec 3, 2009

### Neo_Anderson

The Lorentz Transformations ("LT's") are among the most important system of equations in all of physics. They describe frames of reference (a frame of reference is really nothing more than an observer) that are moving relative to each other.

The LT's show that time slows down when you're moving relative to someone who [thinks] he's stationary relative to you.
The LT's also show that there is a very real, physical 'contraction', or compression of matter; this contraction of matter can only be seen if you are moving relative to a 'stationary' object. What does that mean? That means that if you have a camera that can capture pic's of objects that can move very, very fast (almost speed-of-light fast), and if you take a pic of such a fast-moving object, you will see that object appear 'scrunched up,' as if it is being compressed in the direction of travel.

This is part of the LT:

$$\gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}}$$

If you replace gamma (that "Y"-looking symbol to the left of the equation) with t, and make the right side of the equation equal to t', then you have the equation that describes how slowly a clock ticks as you are moving relative to it. Please note that your watch = t, and the clock's ticks = t'.

15. Dec 3, 2009

### Neo_Anderson

Also cyberfish, please understand that the tachyon is nothing but crackpot physics. It's cocklemamy junk. It's nonsense that tried to account for violations of Bell's inequalities long before better ideas came into being.
Like superstrings, no Physicist takes tachyons very seriously...

16. Dec 3, 2009

### DaveC426913

Tachyons are not crackpot physics. It is true that they are only hypothetical particles, with no evidence to support their existence. That's not quite the same thing as crackpottery. Trying to make use of tachyons for some thing may be crackpottery but that does not make the hypothetical particle crackpottery.

And relativity does not rule them out.

17. Dec 3, 2009

### planethunter

The google books post poses an interesting inference. It states that nothing can travel faster than light in a vacuum. However, something can travel faster than light if the speed of light were to decrease. Thoughts on this?

18. Dec 3, 2009

### DaveC426913

http://en.wikipedia.org/wiki/Cherenkov_radiation" [Broken] had some thoughts on this, yes.

Last edited by a moderator: May 4, 2017
19. Dec 4, 2009

### Neo_Anderson

Tachyons are crackpottery of the highest order.
Suppose noone had ever created the concept of the tachyon. Suppose further that someone comes on this forum and declares that there may be a subatomic particle that can move much faster than the velocity of light, and that this particle is infinitely massive at the speed of light. That's right. He's get his IP banned for bringing crackpot theories to the forum.

20. Dec 4, 2009

### JesseM

If this person supported their arguments with math (specifically the fact that if you set the tachyon's rest mass to be an imaginary number, all its measurable attributes turn out to be real-valued) I don't think the discussion would be banned. And "this particle is infinitely massive at the speed of light" doesn't really make sense, it would be just as impossible for a tachyon to reach the speed of light as it is for a sublight particle to reach the speed of light.

Obviously the causality issues and the complete lack of experimental evidence make tachyons extremely far-fetched, but I don't think they're a crackpot notion.

Last edited: Dec 4, 2009