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Author Topic: Is Relativity Wrong?  (Read 17079 times)

Offline Solvay_1927

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Re: Is Relativity Wrong?
« Reply #25 on: 10/10/2005 22:43:37 »
Secondly, Rincewind:

Some interesting challenges to relativity theory.  Keep them coming, they’re getting me to really use my brain (for a change).

Re: the idea that displacement, not motion, causes time dilation – I think Michael’s example of circular motion dealt with that.  (Nice one Michael – I wish I’d thought of that myself.)

Re: acceleration can’t be the key – hopefully you’ll find the following link as useful and interesting as I did.  (The logic in this web page looks right to me, but I may be missing something.)

http://www.incentre.net/tcantine/TP.html

Re: symmetry in relativity – there IS symmetry in relativity.
You need to get past the notion of ABSOLUTE time and ABSOLUTE space (which relativity says don’t exist), and accept that all we can do is measure the DIFFERENCE in lengths between points, and the DIFFERENCE in times between events.

Relativity is symmetrical in that it says that two observers stationary relative to each other (and ignoring the gravitational field too, to be pedantic) will measure the same rate of ticking of a clock as each other.  Their clocks may have different starting times (9pm and 10pm), but so long as they’re stationary, their clocks will advance at the same rate.

I’ve a feeling (but I can’t prove it … until I’ve studied relativity more) that the symmetry in relativity would be destroyed if time slowed down when an astronaut is moving away from you and sped up when travelling towards you – such that their clocks read the same time again when they rejoin each other.  ((Maybe an example of circular motion would help here too, Michael??))

Symmetry in physical laws can be expressed mathematically by saying that some quantity or other is conserved – i.e. that the quantity is “invariant” (doesn’t change).

You’re right that in normal (“Euclidean”) space - in the absence of motion or gravity - the distance from the origin is “invariant” under rotation.  Mathematically, this is expressed as the invariance of the “Interval” I, where:
I^2 = x^2 + y^2 + z^2.
(That’s just Pythagoras’ rule for a hypoteneuse in 3 dimensions, by the way.)

In relativity, the invariant “Interval” I is calculated as:
I^2 = x^2 + y^2 + z^2 – (c.t)^2

(No, don’t ask me how they derive that.)

The fourth term above, the (c.t) term, is basically agreeing with what you said earlier - that a time difference of 1 second can be treated as equivalent to a length/displacement difference of 300,000 km along a space dimension.  But this (c.t) term is NEGATIVE in the above equation, not positive – which (I think, maybe?) sort of explains the counter-intuitive nature of relativity.  (For example, it means that a rotation of the axes - due to motion – leads to time differences dilating and lengths contracting, rather than length and time keeping their normal relations to each other.)

Maybe I’m not actually helping here (someone who doesn’t really understand what he’s talking about quoting mathematical formulae at you) – but you started it with your (0,0,5) coordinates!  [:p]
 

Offline Solvay_1927

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Re: Is Relativity Wrong?
« Reply #26 on: 10/10/2005 22:50:16 »
Finally, can I suggest a couple of good (and cheap) books if you really want to get your head around relativity.

“Six Not-So-Easy Pieces” by Richard Feynman is a collection of 6 lectures (from the Feynman Lectures in Physics Vols I and II) that give an excellent grounding in relativity (and symmetry).  It uses some “high school” maths, but I imagine it’s still useful even if you skip a lot of the maths.
(I’ve recently finished reading it.  Obviously, I plan to read it a second time, in the hope that I'll actually understand it better on a second reading!)

And I've just started reading "Understanding Einstein's Theories of Relativity" by Stan Gibilisco - it looks very good too (simple explanations and lots of diagrams).

Right, I've written enough now to send everyone to sleep, so it's time for me to shut up again.


"The early bird may get the worm, but it's the second mouse who gets the cheese."
 

Offline McQueen

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Re: Is Relativity Wrong?
« Reply #27 on: 11/10/2005 00:41:06 »
To the question : Is relativity wrong ? Probably the answer should be that  relativity is wrong for macroscopic objects. No macroscopic objects have ever been observed to travel anywhere near the speed of light , so none of the things to do with relativity need apply. The earth itself is revolving around the sun at about 28,000 m/sec. which is about 0.00009% of the speed of light ,  at these speeds the effects of relativity are negligible. Relativity does apply to sub-atomic particles and a lot of evidence has been found in support of it . For instance electrons accelearted to near the speed of light show an increase in mass of  11,800 times the electron at rest. And sub-atomic particles formed as a result of cosmic radiation striking the earth's atmosphere have been found to have life times 6 times as long as those made in the laboratory because they were travelling through the atmosphere at near the speed of light. Relativity is more to do with objects travelling at relativistic velocities , than with ordinary objects travelling at ordinary velocities.
« Last Edit: 11/10/2005 01:18:54 by McQueen »
 

Offline Solvay_1927

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Re: Is Relativity Wrong?
« Reply #28 on: 11/10/2005 13:13:05 »
McQueen,
just because the effects of relativity are hard to measure (because they're so small) for macroscopic objects doesn't mean that relativity is "wrong" for macroscopic objects and only applies to sub-atomic particles!

Also, don't forget general relativity (GR).  Special relativity (SR) only covers uniform velocities, but Einstein extended it to accelerated motion and gravity via GR.  And the effects of GR have been experimentally verified (e.g. bending of light rays passing near the sun, oddities in the orbit of Mercury).

But then, while SR does apply to sub-atomic particles, they can't find a way of making GR work with such quantum particles (the elusive "theory of everything" / "quantum gravity").

"The early bird may get the worm, but it's the second mouse who gets the cheese."
 

Offline McQueen

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Re: Is Relativity Wrong?
« Reply #29 on: 11/10/2005 14:48:26 »
Paul ( Solvay 1927)

It was not my intention to say that time dilation only worked at the sub-atomic level , what I did want to say was that the effects are so small , that they are almost neglible in any real terms for instance in the example given in the starting post of the thread, time dilation for the astronauts might mean an increase in life time of about 0.0000001 secs , ( see :  http://www.btinternet.com/~j.doyle/SR/sr4/sr4.htm ).  On the other hand these figures are still understandable , if we take the matter wave associated with a car weighing 1 ton and moving at 10 km/hr we get a length of 10 ^-38m(approx.) which is totally unacceptable.
 

Offline Rincewind

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Re: Is Relativity Wrong?
« Reply #30 on: 12/10/2005 14:30:27 »
Why is that unacceptable?  When you say matter wave, does that mean the electromagnetic wave associated with the car's kinetic energy?

Excuse my ignorance:)

Solvay, so basically it's like adding the time coordinate to the space ones if time were an imaginary dimension and space's dimensions were real (as in imaginary/real numbers).  Funky.  Hm, I think that's what I thought.  I mean I hadn't expressed it mathematically, or realised that it meant that time was imaginary but that when something was further away from you it was behind you in time, in a manner of speaking, and that if it moved toward you it would move forward in time to meet you.
 

Offline McQueen

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Re: Is Relativity Wrong?
« Reply #31 on: 12/10/2005 15:20:07 »
Andrew (Rince)

Matter waves , ( I feel )  are unacceptable because in terms of reality they represent infinities. It is unrealistic to talk of waves 10^ -38m long. ( and this for an object only weighing 1000 Kg and traveling at 10Km/hr ) Now if you look at Einstein’s equations they are always within reason. Even an object moving at a few millimeters a second would come within realistic ( excuse the pun ) limits.  

Your second comment dealing with time co-ordinates , is interesting. (This applies to Solvay too. )  Personally ( and this is not saying much ) I do not believe in General Relativity.  For me the space time continuum , represents a state where the speed of light can be exceeded. Imagine the scene in a fairly restricted space such as earth , dimensions no longer exist , because you can be in any place you want faster than you think, It would make no difference if you are in Rome or London because you could get there faster than thought , in fact you could be in both places at once ! Time would no longer exist. In such a situation you could be taking off from Heathrow to the States , and arriving there ( at Heathrow )  in another plane , just as your plane is taking off . So theoretically you could be in two , three or four places at the same time. What is amazing is that QM supports this view in its “Many World’s Theory. In truth reality is not like that. Everything observable in the Universe is governed by the limitations imposed by the speed of light. So , although space and time may in fact be , in some as yet not understood manner , related , it certainly would not have anything to do with gravity , which I believe , is a function of the ether.
 

Offline Solvay_1927

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Re: Is Relativity Wrong?
« Reply #32 on: 13/10/2005 00:54:58 »
Rinceandrew - re: your comments on time being (at least mathematically) like an imaginary dimension - as in SQRT(-1) - that sounds sort of right to me.


"The early bird may get the worm, but it's the second mouse who gets the cheese."
 

Offline Rincewind

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Re: Is Relativity Wrong?
« Reply #33 on: 13/01/2006 00:48:45 »
But, doesn't it work out that the mass of a body tends to infinity as it's velocity tends to the speed of light?  Or is that a false assumption that I've picked up from somewhere? (I've done a lot of learning by talking so I'm never quite sure of my facts)

I think we could reach the speed of light if we somehow, rather than adding extra kinetic energy, we converted our rest mass into pure kintic energy or em radiation or whatever you want to call it, then managed to re-focus it, re-congeal it, turn it back into rest mass basically (a la Star Trek).  But I don't think we can go faster than it.  But I'm open to argument, no TOEs or GUTs have shown up yet:)
 

Offline ukmicky

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Re: Is Relativity Wrong?
« Reply #34 on: 13/01/2006 01:10:33 »
quote:
But, doesn't it work out that the mass of a body tends to infinity as it's velocity tends to the speed of light? Or is that a false assumption that I've picked up from somewhere? (I've done a lot of learning by talking so I'm never quite sure of my facts)

Correct the relativistic mass of the object will become infinite if it approaches the speed of light.

Michael                 HAPPY NEW YEAR                    
 

Offline Rincewind

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Re: Is Relativity Wrong?
« Reply #35 on: 13/01/2006 01:42:00 »
Hey Mickey, you're still here:)

and Solvay, I followed that link about time dilation (you've probably forgotten about it by now but if you do remember...).  At first I thought it wasn't relevant because the example isn't a return trip, it's one way.  Then I thought it might kinda make sense.  Then I thought it wasn't really relevant because a fraction of a second later the rest of the train or whatever would catch up and, I suppose the average amount of time your body, or your brain, or whatever parts of your brain perceive time, or your watch, or your radiation meter, has experienced as to how much time has passed.  And my point was that if you got back to the same place, you'd be back in the same time as the people who hadn't moved.  Otherwise what's that coordinates thing all about? I don't think that link really addresses that, but it took some brain bending to get me head around it so I'm not sure I've got it right.
 

Offline ukmicky

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Re: Is Relativity Wrong?
« Reply #36 on: 13/01/2006 01:54:56 »
Cant remenber mate but i do remember you:)

Michael                 HAPPY NEW YEAR                    
 

Offline Soul Surfer

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Re: Is Relativity Wrong?
« Reply #37 on: 13/01/2006 10:43:41 »
I have just caught up with this long thread and think that those anti relatavists have forgotten one important detail.  The original reason that Einstein started on the theory and its rather non intuitive results, was that the most fundamental laws of the universe are: energy and angular momentum are conserved (ie you don't get something for nothing) and the laws of physics are much the same wherever you are.  The rest follows.

As has been clearly demonstrated the fine dtails have been and are contiually being confirmed on a daliy basis.

OK  there may well be some deviations in very extreme conditions and these are continually being questioned and investigated but they are certainly no problems with relativitiy as a small correction to classical Newtonian gravity anywhere we are likely to go.

Learn, create, test and tell
evolution rules in all things
God says so!
« Last Edit: 13/01/2006 10:45:53 by Soul Surfer »
 

Offline Solvay_1927

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Re: Is Relativity Wrong?
« Reply #38 on: 14/01/2006 02:06:40 »
quote:
Originally posted by Rincewind

Hey Mickey, you're still here:)

and Solvay, I followed that link about time dilation (you've probably forgotten about it by now but if you do remember...).  At first I thought it wasn't relevant because the example isn't a return trip, it's one way.  Then I thought it might kinda make sense.  Then I thought it wasn't really relevant because a fraction of a second later the rest of the train or whatever would catch up and, I suppose the average amount of time your body, or your brain, or whatever parts of your brain perceive time, or your watch, or your radiation meter, has experienced as to how much time has passed.  And my point was that if you got back to the same place, you'd be back in the same time as the people who hadn't moved.  Otherwise what's that coordinates thing all about? I don't think that link really addresses that, but it took some brain bending to get me head around it so I'm not sure I've got it right.



Hi Andrew, welcome back, long time no see.

But I'm afraid I'm clueless about the time dilation link you refer to.  (Can you remind us?)
 

Offline Solvay_1927

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Re: Is Relativity Wrong?
« Reply #39 on: 14/01/2006 02:12:11 »
Oh, sorry, I just looked back on page 1 of this thread and realised what you were referring to.

All I can say is ... I'm still confused by all this relativity business! :D
 

Offline ukmicky

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Re: Is Relativity Wrong?
« Reply #40 on: 14/01/2006 02:58:18 »
quote:
 Oh, sorry, I just looked back on page 1 of this thread and realised what you were referring to.


Me too[:I]



Michael                 HAPPY NEW YEAR                    
 

Offline madmortigan

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Re: Is Relativity Wrong?
« Reply #41 on: 17/01/2006 21:30:42 »
Hi there

Just went through the discussion quickly, so I may have missed something.

One main problem I see with the reasoning is the attempt to apply special relativity to a problem that includes non-inertial systems of reference.

The twins paradox is only brought up in text books to demonstrate the weirdness of relativity, when compared to newtonian mechanics. However, it can't bedescribed fully in the scope of general relativity. The key point is that the astronaut twin leaves the earth - ie, accelerates to a speed, travels for so long, then comes back, etc. This is not an inertial reference system.

If you don't take into acount accelerations, you end up with a very symmetrical situation. The astronaut twin travels at a certain speed with respect to the earth twin. But, the same goes for the earth twin (ok, take him of the earth, and put him on a space station). He also travels with the same certain speed (opposite direction) with respect to the astronaut.

The difference between the two is that the twin who leaves earth accelerates to a certain speed, etc. as I said earlier.

Don't ask me to describe what's up in the twins paradox in term of general relativity!!

 

Offline madmortigan

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Re: Is Relativity Wrong?
« Reply #42 on: 17/01/2006 21:31:23 »
Hi there

Just went through the discussion quickly, so I may have missed something.

One main problem I see with the reasoning is the attempt to apply special relativity to a problem that includes non-inertial systems of reference.

The twins paradox is only brought up in text books to demonstrate the weirdness of relativity, when compared to newtonian mechanics. However, it can't bedescribed fully in the scope of general relativity. The key point is that the astronaut twin leaves the earth - ie, accelerates to a speed, travels for so long, then comes back, etc. This is not an inertial reference system.

If you don't take into acount accelerations, you end up with a very symmetrical situation. The astronaut twin travels at a certain speed with respect to the earth twin. But, the same goes for the earth twin (ok, take him of the earth, and put him on a space station). He also travels with the same certain speed (opposite direction) with respect to the astronaut.

The difference between the two is that the twin who leaves earth accelerates to a certain speed, etc. as I said earlier.

Don't ask me to describe what's up in the twins paradox in term of general relativity!!

 

Offline Rincewind

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Re: Is Relativity Wrong?
« Reply #43 on: 17/01/2006 22:17:29 »
Can anyone tell me what branch of physics or what version of relativity the interval equation comes from?  The one Solvay said: I = x2 + y2 + z2 - t2 (we should have superscript on a science forum really)

Cos if I is invariable then that basically says what I was saying at the start, and it excludes the twins paradox (as I understand it).


I don't really know the differences between special and general.  I thought special was wrong because Einstein had invented a constant to make the results fit the static universe model. If this is true what's the point of special since general came along?

(guessing from madmortigans post - general takes into account acceleration while special just talks about relative velocities, but please expand and/or correct that guess)
 

Offline madmortigan

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Re: Is Relativity Wrong?
« Reply #44 on: 17/01/2006 23:38:13 »
General relativity describes accelerating reference frames. Its math is hard. Special relativity is much easier and can be done with college level math. Thus I strongly suggest getting a textbook and solving all the problems - shouldn't take long. Popular science - although quite fascinating, doesn't give enough hard facts for anyone who feels curious about stuff.

Tha famous constant for anti-gravity was invented by Einstein in the scope of general relativity, right before Hubble poseted his findings on galaxies moving away from each other, thus suggesting an expanding universe.  

I'll go back to check that equation, but I've got to go now, need to file my tax return (speaking of relativity and the lot!)

go with the force!
« Last Edit: 17/01/2006 23:40:09 by madmortigan »
 

Offline Solvay_1927

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Re: Is Relativity Wrong?
« Reply #45 on: 22/01/2006 23:31:23 »
Andrew,
the invariant spacetime interval I = x^2 + y^2 + z^2 - (ct)^2 comes from relativity - I think it's specifically from the attempts (by Minkowski?) to give a geometrical interpretation to relativity.  And note that it applies to special as well as general relativity.

MadMort's right that the only difference between special and general is that the former (1905) only applied to inertial (uniform constant motion or rest) frames of reference, whereas the latter (1914/15) extended that to non-inertial (accelerating) ones.  The special theory is just a "special case" of the general one - it's not wrong, it's just "incomplete".

The "cosmological constant" that you're getting confused about is a "fudge" that Einstein put into his general relativity formula to ensure that the universe was static.  He later said that this was his "greatest blunder" because his theory (without including this "fudge" constant) predicted that the universe was expanding.  So if he'd left the constant out and said "I predict the universe must be expanding", he'd be looking very smug when Hubble confirmed this prediction in the late 1920s.

Hope that helps.
Paul.
 

Offline Rincewind

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Re: Is Relativity Wrong?
« Reply #46 on: 23/01/2006 02:24:21 »
Cheers geez, that's brilliant:)  

You know, when there's something you should know and should have known a long time ago, but have only just found out?  Like a fog lifting, nice one:)
 

Offline Rincewind

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Re: Is Relativity Wrong?
« Reply #47 on: 23/01/2006 02:27:59 »
Dya see what the equatino means, yeah?  If you reduce the three spatial dimensions to a resultant distance s, you get I = s^2 - ct^2... hang on, where'd that c come from?  Musta missed that the first time round, What does that mean?

I'll get back to you
 

Offline Rincewind

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Re: Is Relativity Wrong?
« Reply #48 on: 23/01/2006 02:49:13 »
the distance two events are from each other, minus the distance light has travelled in the time between these events, is invariant.  

Hmm, must sleep, but thanx for clearing up the relativities for me.
 

Offline allmee

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Re: Is Relativity Wrong?
« Reply #49 on: 23/01/2006 08:46:17 »
The peaple on the space ship would percive a diferance to the peaple on the earth but the ship wood be in red fase going awaiy and blue fase coming back so were is the time diferance.
sorry for the speeling, Half a bottle of op rum
 

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Re: Is Relativity Wrong?
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