# Something fishy about special relativity?

1. Oct 22, 2012

### Neandethal00

The reason there are so many paradoxes is there is something fishy about Special Relativity (not General Rel) that no one can pin point it but many sense it.

Mathematically SR can NOT be proven wrong.
Experimentally SR can NOT be proven wrong.

IMHO, the reason may lie in our very basic definition of speed. Speed = Length/Time.
Interestingly, speed affect both Length and Time (mass comes later).

We may be going in cycles here, speed-->length-->time-->speed.....
It doesn't matter how you introduce one variable others will produce predicted results.

2. Oct 22, 2012

### phinds

Re: List of Special Relativity Paradoxes.

Uh ... good luck with that thought.

Yep. Kind of hard to see how it can be wrong in any sense when, as you just stated, it can't be wrong in any sense.

3. Oct 22, 2012

### tiny-tim

what's wrong with being fishy?

4. Oct 22, 2012

### pervect

Staff Emeritus
Re: List of Special Relativity Paradoxes.

Oh, for the most part it's pretty easy to see where people go wrong in trying to understand SR. It's when they hold on to notions of absolute time.

One identifying characteristic of absolute time is this - if two objects take different paths through space-time, you expect their clocks to agree at the end.

Absolute time would be a logical consequence of everyone sharing the same concept of "now". Using this universal concept of "now", one could map any instant of time that one experienced to "absolute time", either on some central, "absolute clock", or a network of absolute clocks all synchronized by the "absoute now".

Relativity doesn't have either a universal "now" or a concept of absolute time, however.

While the notion of non-absolute time appears to be the root of the problem, a lot of people with this fundamental issue seem to misidentify the problem, and start building up elaborate mental defense systems to attempt to rationalize away the problems. These defense mechanisms can become more of an obstacle than the original problem, and are highly varied and somewhat unique to the individual. I was tempted to go into details, but it's probably best if I don't.

5. Oct 22, 2012

### Staff: Mentor

Re: List of Special Relativity Paradoxes.

The overwhelming majority of these paradoxes fall in one or more of three categories:
1) A paradoxical and internally inconsistent conclusion results from fallaciously assuming perfectly rigid objects; bug-rivet is an example.
2) A paradoxical and internally inconsistent conclusion results from fallaciously assuming absolute time and ignoring the relativity of simultaneity. The tipoff for these is usually words like "at the same time" or "the same rate" appearing.
3) As with the so-called twin paradox, there's no paradox, just a surprising result.

I don't see how any of these suggest any underlying fishiness in SR, any more than the following derivation:
x = 1
x2 = 1
x2 - 1 = 0
(x+1)(x-1) = 0
x+1 = 0
2 = 0
suggests that there's something fishy about algebra.
I just slipped in a division by zero at the next-to-last step, and the "paradox" disappears as soon as you notice it. That's the moral equivalent of slipping "at the same time" into a relativity thought experiment; the paradox lasts only as long as you don't notice the error.

Last edited: Oct 22, 2012
6. Oct 22, 2012

### ghwellsjr

Re: List of Special Relativity Paradoxes.

If you're saying that since x = 1 then (x-1) = 0, and you "divide by zero" but then you get:

(x+1) = 0/0 which is indeterminate, meaning it can take on any value, including 2.

This only works for people who think that 0/0 can only be 0 instead of any value.

7. Oct 22, 2012

### pervect

Staff Emeritus
Re: List of Special Relativity Paradoxes.

My list was shorter, but offhand I'd say that the real issue in believing in a rigid object is the relativity of simultaneity. A rigid object requires a notion of simultaneity for the object to be "rigid" in. I.e. if you want to say an object is rigid because the front moves at the same time as you push the back, you need a definition of "at the same time".

It's not paradoxical to have Born rigid motion in SR (though it does require pre-planning to make an object move in a Born rigid manner). I'd say that the paradoxes come about when one believes that all rigid object's share a universal notion of simultaneity.

8. Oct 22, 2012

### Staff: Mentor

Re: List of Special Relativity Paradoxes.

... or for people who didn't notice that the divisor was zero and reflexively evaluated 0/(x-1) to zero, as would be correct if x-1 were known to be non-zero.

.... and special relativity paradoxes only work for people who think that there is an absolute time (or absolutely rigid bodies, or...). The point I'm trying to make is that the existence of SR paradoxes no more indicates "fishiness" in SR than the existence of bogus derivations such as the above indicates a problem with elementary algebra. On the contrary, they're opportunities to learn by finding the hidden error.

9. Oct 22, 2012

### ghwellsjr

Re: List of Special Relativity Paradoxes.

I see now what you are saying but it would have been a lot more effective for me if you had included the step:

(x+1) = 0/(x-1)

I was assuming that you were dividing the two equations:

(x+1)(x-1)/(x-1) = 0/0

10. Oct 22, 2012

### Staff: Mentor

Re: List of Special Relativity Paradoxes.

I'm inclined to agree with you - I debated including that one in my list, decided to do so because so many beginners see the rigidity problems as a way to get around RoS, not a consequence of it.

Too often I've seen someone work through all the trains and mirrors and lightning bolts... finally hit their eureka moment and say they've gotten it... and then come back next day with a story that starts "I have this rigid rod, and one end of it is touching a detonator, and I push on the other end....".

11. Oct 22, 2012

### Staff: Mentor

Re: List of Special Relativity Paradoxes.

Ah - right. I never was a very good stage magician, just never did get effective misdirection figured out :-)

12. Oct 22, 2012

### Neandethal00

Re: List of Special Relativity Paradoxes.

When I read about paradoxes and their rebuttals, neither convince me much. Not that convincing me matters. IMHO both party suffer from forced rationalization.

I'm surprised they have gone to such an extend as flying a plane around the globe for days to prove Time Dilation, when they can now use the space station. The station is moving at 4.78 miles/sec. A simultaneous experiment on earth and on the station counting GHz pulses for days can clearly prove time dilation.
Better yet, by measuring and accumulating long Time Constants of two identical RC circuits can prove not only time dilation but also effects of time dilation on electronic circuits.

13. Oct 22, 2012

### Staff: Mentor

Re: List of Special Relativity Paradoxes.

We've been doing that for years already. The clocks on GPS satellites run at a different rate from earthbound clocks (in their own rest frames), to compensate for relativistic effects. This includes both the speed-dependent ("SR") effect and the altitude-dependent ("GR") effect.

To test this, when the first GPS satellite (or one of the early ones, at least) went into orbit, the correction was initially disabled. The satellite clock ran at the rate predicted by relativity. Then the correction was turned on for "production" purposes.

http://relativity.livingreviews.org/Articles/lrr-2003-1/ [Broken]

Last edited by a moderator: May 6, 2017
14. Oct 22, 2012

### ZapperZ

Staff Emeritus
Re: List of Special Relativity Paradoxes.

This is utterly silly. Not only are things like this routinely done via the GPS (as stated already), but why would an RC circuit be ANY better or more accurate than all the other experiments, such as this one?

http://physicsworld.com/cws/article/news/2010/sep/24/relativity-with-a-human-touch

And it self-defeating to talk about "A simultaneous experiment" without having a clue on what that means and how to determine that something is occurring "simultaneously", something that needs careful attention when dealing with relativistic effects.

I think you are the one suffering from "forced rationalization", or maybe "false rationalization".

Zz.

15. Oct 22, 2012

### Staff: Mentor

Re: List of Special Relativity Paradoxes.

True.
False. See http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html If any of those experiments had produced different results then SR would have been proven wrong. It is imminently falsifiable, otherwise it wouldn't be scientific.

16. Oct 22, 2012

### Staff: Mentor

[No] thanks for hijacking the thread that this (and the following responses) were originally posted to. Please note the sticky post at the top of this forum: