The Light Speed Barrier - Is there really a universal speed limit?

Spider-Man · 2003-09-02 00:53:23

I would like to make a side note that, if gravity moved at such speeds as proposed in "Rethinking Relativity", and originally by Tom van Flandern, the need for "dark matter" in the universe is eliminated, and the problem of the astronomical movements of stars around galaxies like our own is completely explained, and without the need for invisible matter that keeps things connected.

In all fairness, I should inform those who weren't aware that, earlier this year, a paper was published suppos?dly confirming that the speeds of light and gravity are identical:

http://www.space.com/scienceastronomy/g … 30107.html

It was really quite disheartening, but after reading it, I didn't buy it. In fact, the same sort of nonsense that pervades all modern fields of science is quite evident; let me take a quote out of the article:

Craig Hogan...said the very high-precision measurement was the first to check whether Einstein's assumption about gravity was correct.
"Thankfully, it is," Hogan said, adding that were it not, theorists would have their hands full trying to explain the result.

You see that physicists aren't concerned with finding the truth. That would be too much trouble, no, they try to cover their arses and defend their university seats with all ardence and antiquated stubbornness. They're as bad as NASA, not exploring, but idling.

Ah, but here is a counter article that tells how the original report is revealed as being full of holes:

http://www.space.com/scienceastronomy/g … 30116.html

That one is definitely worth reading.

I thought the following figures were interesting when I multiplied them out ? Suppose the speed of gravity is 20 billion times that of light. That would give it a velocity of 3.72 x 10^15 miles per second, 6 x 10^15 kilometers per second. Naturally, such abstract numbers have little relevance without a context or frame of reference. So, I took the liberty of making a few calculations:

The distance to the Centauri star system, our closest stellar neighbor, is 4.3 light years. That means it takes about four years, three months, and three weeks for light to travel from here to Alpha Centauri, or vice versa. Divided by 20 billion, that means the number of gravity-years between here and Centauri is 2.15 x 10^-10. Again, this doesn't mean much to you and me.

So, let's do it in the number of days; it takes 1571 days for light to go between Sol and Centauri. That makes 7.85 x 10^-8 days for gravity. Once more, no real meaning.

Calculating down, it would take 1.88 x 10^-6 hours for gravity to travel that distance, only 1.13 x 10^-4 minutes. This means that it only takes 0.00678 seconds for gravity to travel between here and the closest star system!
In literally less time than it takes for you to blink your eye, Alpha Centauri has been affected by the contraction of your eyelid muscles, by the very gravitational influence of the electrons that trigger the muscle fibers to move in the first place. Such speed is almost unthinkable. Just imagine the possibilities for communication!

Well then, let's see what happens when trying to send messages across the galaxy utilizing gravity. The Milky Way is 80 thousand lightyears across, or 2 x 10^-6 gravity-years. That's 7.31 x 10^-4 gravity-days, 0.018 gravity-hours, or just 1.052 gravity minutes! In 63 seconds, gravity crosses the entire galaxy.

And then what of the whole universe itself? Well, the visible universe is estimated at approximately 20 billion light-years across ? and since gravity moves 20 billion times faster than light in our postulations, it would take about one year for gravity to cross the universe. The movement of your eyeballs right now as you read these words is having an effect, though truly miniscule beyond description, on the quasars at the edge of space and time. And they, in turn, are having an effect on you. We are all connected, through and through, with every bit of the universe, from the largest black whole to the smallest electron, by the true Force.

The stars, the contellations of astrology, really do have an effect on us after all.

Lone--Wolfe · 2003-09-02 19:25:42

well, theres ur smart cookies...

space_psibrain · 2003-09-05 22:04:49

well...its not as if we didn't know scientists fudge their data to supprot their conclusions...

Gennaro · 2003-09-09 09:13:18

Absolutely fascinating.

Thanks, that article and your reasoning was probably the best explanation on the GPS phenomena discussion and its implications on special relativity as well as the challenge from the speed of gravity, you can find on on the net. Great effort, Spider-Man!
I'll pass it on to friends & relatives.

'We are all interconnected'. Maybe we are even witnessing the beginnings of a paradigmatic shift in thinking here? From an era of 'light' and subjectivity to an era of 'gravitation' and objectiveness as the main departure for reasoning about the physical world?

Forgive me, but I almost feel like quoting Pope:

Nature and Nature's laws lay hid in night,
God said "Let Newton be!" and all was light.
:;):

Shaun Barrett · 2003-09-26 20:26:46

Hi SpiderMan!
I've been meaning to thank you for your post here which included the "Rethinking Relativity" excerpt. Having just read your reply over in 'Science and Technology' to my post about Higgs Bosons etc., I was reminded of my omission and thought I should do something about it!
This apparently re-emerging concept of a universal ether is very interesting. I can see how it might offer us a simpler explanation for many of the phenomena which we currently resort to time-dilation and curved-space-time to explain. If the physicists involved could get together and write a comprehensive and watertight explanation for all observed data, using the ether, then the scientific world would surely have to sit up and take notice.

One detail I'm having trouble with concerns the slowing of clocks which move through the ether. The idea put forward is that all physical processes, down to the orbiting of electrons about their respective atomic nuclei, are made slower by their "ploughing through this medium and working more slowly".
I can grasp why a clock in a gravity well, like Earth's where the ether is denser, should work more slowly than an identical clock out in interplanetary space, where the ether is more attenuated. But why should movement of a clock through the ether cause any more difficulty than exists in a stationary clock in the same density of ether? The movement of an electron might slow when it's against the 'ether breeze' but, as it comes around the nucleus, wouldn't it speed up as it moves with the 'breeze'? This is a simplistic question, I know, but I'm merely making the point that, in an oscillating system moving through a viscous medium, half the motions will be helped and half will be hindered at any given moment, thus resulting in a neutral effect by the medium. (True? )
Another point about this hypothesised ether relates to its apparent susceptibility to gravity. If it is attracted by a gravitational field, and thus accumulates around massive bodies, why does it exist in any appreciable amounts at all away from stars and planets? Or is there, in fact, none of it between the stars at all? But then, haven't time-dilation effects been observed in relatively short-lived particles arriving at Earth from millions of light years away, as though they must have been travelling through the ether (or experiencing time-dilation, according to Einstein)?
Just some idle thoughts.

P.S. Many thanks, by the way, for your kind words over at 'Science and Technology' regarding my writing.

sethmckiness · 2003-09-27 09:27:58

This is simply too good to be true..

This is just awesome.. I was waiting for something like this. Seems reminiscient of 1947 and the Bell X-1, piloted by a Captain in the newly formed United States Air Force that noone had ever heard of.

So, once we actually find this damn gravitron or whatever they call it, it could be great for communications and maybe for propulsion... who needs a solar sail...

sethmckiness · 2003-09-27 09:33:32

This is simply too good to be true..

This is just awesome.. I was waiting for something like this. Seems reminiscient of 1947 and the Bell X-1, piloted by a Captain in the newly formed United States Air Force that noone had ever heard of.

So, once we actually find this damn gravitron or whatever they call it, it could be great for communications and maybe for propulsion... who needs a solar sail...

Spider-Man · 2003-09-27 17:29:28

Hi SpiderMan!

Heya, Shaun!

I've been meaning to thank you for your post here which included the "Rethinking Relativity" excerpt. Having just read your reply over in 'Science and Technology' to my post about Higgs Bosons etc., I was reminded of my omission and thought I should do something about it!

Much appreciated. *Smiles.*

This apparently re-emerging concept of a universal ether is very interesting. I can see how it might offer us a simpler explanation for many of the phenomena which we currently resort to time-dilation and curved-space-time to explain. If the physicists involved could get together and write a comprehensive and watertight explanation for all observed data, using the ether, then the scientific world would surely have to sit up and take notice.

I agree.

One detail I'm having trouble with concerns the slowing of clocks which move through the ether. The idea put forward is that all physical processes, down to the orbiting of electrons about their respective atomic nuclei, are made slower by their "ploughing through this medium and working more slowly".
I can grasp why a clock in a gravity well, like Earth's where the ether is denser, should work more slowly than an identical clock out in interplanetary space, where the ether is more attenuated. But why should movement of a clock through the ether cause any more difficulty than exists in a stationary clock in the same density of ether? The movement of an electron might slow when it's against the 'ether breeze' but, as it comes around the nucleus, wouldn't it speed up as it moves with the 'breeze'? This is a simplistic question, I know, but I'm merely making the point that, in an oscillating system moving through a viscous medium, half the motions will be helped and half will be hindered at any given moment, thus resulting in a neutral effect by the medium. (True? )

Genious, my friend!

Ya see, this is where Einstein f*cked up, if I may invoke the profanity. Einstein is very clear, if you read Relativity, his book on the subject, that it is not velocity, but acceleration which causes time dilation. You can go as fast as you want, but if it's at a constant velocity, you won't experience time dilation anymore than you will experience artificial gravity (G-forces).

Indeed, it's acceleration that he compares to gravity, because acceleration produces an artificial sort of gravity. And because they were virtually the same, he thought that time would be affected in the same way, and voil?, General Relativity.
Now, let's examine what happens with consideration to the ether: If an atom is accelerating, the electron is going to experience a greater drag each time it makes an orbit about the nucleus, and will slow down more and more as its acceleration increases. But once it comes to a constant speed, the electron, you're absolutely right, should orbit at a normal, natural speed. The same is true of molecular vibration, phonons, superstructures, et cetera.

Einstein was pretty certain about the acceleration thing... but then... *Laughs.*... in his very own equations, Einstein equates acceleration with velocity! or at least those who have formed them into their own work. It's a terrible confusion, one that is most reprehensible.

Another point about this hypothesised ether relates to its apparent susceptibility to gravity. If it is attracted by a gravitational field, and thus accumulates around massive bodies, why does it exist in any appreciable amounts at all away from stars and planets?

Because it's not actually a fluid or made of mass or particles, likely, but instead acts much more like a fabric (indeed, the fabric of spacetime), so that it can be stretched, but isn't sucked away entirely from an area, as water or gas would be.

Or is there, in fact, none of it between the stars at all?

Well, photons are just vibrations of the ether, theoretically; so if there were no ether between us and any star, we shouldn't be able to see that star.

But then, haven't time-dilation effects been observed in relatively short-lived particles arriving at Earth from millions of light years away, as though they must have been travelling through the ether (or experiencing time-dilation, according to Einstein)?
Just some idle thoughts.

And very good ones.

P.S. Many thanks, by the way, for your kind words over at 'Science and Technology' regarding my writing

The pleasure was mine to read it, friend.

Shaun Barrett · 2003-09-29 07:24:56

Hi again SpiderMan!
Your quote:-

Einstein is very clear, if you read Relativity, his book on the subject, that it is not velocity, but acceleration which causes time dilation.

I don't believe this is actually the case. As I understand it, Special Relativity specifically links time dilation to velocity, not acceleration.

I think I also understand what you are referring to when you compare gravity and acceleration. Einstein did this in his General Relativity, where he established 'The Principle of Equivalence', which essentially states that the acceleration of a body being pushed faster and faster produces effects on that body indistinguishable from a gravitational field of equal strength in which that body is stationary. In other words, if you were in a box in outer space being accelerated smoothly and silently at 9.81 m/s/s, the sensation would be exactly the same as if you were in a box sitting stationary on the surface of the Earth.
Einstein therefore established that inertial mass is identical to gravitational mass and, since photons have momentum and must therefore have inertial mass attributed to them, they must also have gravitational mass and should be affected by gravity. As we know, experiments seem to have confirmed that gravity bends the path of light. (Ether being the alternative explanation, as we've discussed.)

I know Einstein maintained, too, that a gravitational field slows time just as velocity does. But I don't think he meant to imply that time dilation is caused by acceleration alone and not by velocity.
If he had done so in his General Relativity, it would have been a direct contradiction of what he said in Special Relativity. Such an obvious contradiction would have been unthinkable and would have been noticed and pulled to pieces.

Of course, I barely understand Special Relativity, and haven't the foggiest notion of how the mathematics in General Relativity works!!

So, if I'm missing something important here:-
a) It won't surprise me at all, and
b) I'm happy to be educated. (In accordance with the K.I.S.S.
Principle, naturally! )

dicktice · 2003-09-29 17:56:01

Shaun/Spider: I can't imagine constant velocity affecting relative time, but acceleration alone. After all, the "atomic clocks" orbiting Earth are constantly accelerating, right? But Spider--I really have a problem with your use of the term "Ether," because there ain't no such thing! Now, I'll go back and read what you two were on about in the preceding posts--sorry to be rude.

Spider-Man · 2003-09-29 22:08:30

I know Einstein maintained, too, that a gravitational field slows time just as velocity does. But I don't think he meant to imply that time dilation is caused by acceleration alone and not by velocity.
If he had done so in his General Relativity, it would have been a direct contradiction of what he said in Special Relativity. Such an obvious contradiction would have been unthinkable and would have been noticed and pulled to pieces.

Not necessarily. I've taken a gander into the equations, and they are so befuddledly complex and peculiar (mainly patched together from work by previous physicists) that velocity and acceleration are actually confusable as the same property.

Besides, it doesn't make sense for acceleration and gravity to be exactly the same with regard to everything except time dilation. Indeed, your explanation, and a very good one it is, very precisely makes that point, even though you contradict your wisdom at the end there.

Shaun/Spider: I can't imagine constant velocity affecting relative time, but acceleration alone. After all, the "atomic clocks" orbiting Earth are constantly accelerating, right?

Absolutely; they show time dilation, not because they are going faster than relatively stationary positions on Earth, but because they are constantly going in a circle ? any object moving in a circular path is constantly accelerating, that is, changing its velocity, its direction, even though its relative speed remains constant. Indeed, with regard to the aether (I prefer the more archaic spelling, as it was in Latin), this makes much, much more sense, for an object that is moving in a circular path in a medium of some kind will experience effects very similar to those as if it were merely accelerating in a straight line (pressue bow waves).

I think the main problem in modern astrophysics is taking Einstein's word as gospel. He was wrong, many times, love him as we do. I don't know why he insisted there be no aether of any kind, perhaps because he didn't want fluid-wave dynamics to interfere with the real physics of light, but none of his ideas make any sense without it.

But Spider--I really have a problem with your use of the term "Ether," because there ain't no such thing! Now, I'll go back and read what you two were on about in the preceding posts--sorry to be rude.

*Smiles.* It is rude. You should have read the three major posts I compiled above, the first being the article on Rethinking Relativity. Then move to the consequential discussion.

dicktice · 2003-10-01 08:33:20

Spider, with apologies to Shaun:
I wuz wrong,wrong,wrong. Time dialation IS the result of relative velocity, acceleration being merely the rate at which the velocity reaches some limiting relative magnitude. Having stated the obvious, and before I go back to read your previous (three?) major posts, please consider the following thought experiment which I (emulating the great Einstein) have just thunk up for you to tear apart:
A rogue space consortium irresponsibly launches a polar surveillance space vehicle in the opposite direction from an establishment vehicle already in orbit. It carries a flashing-light beacon which is picked up by sensors on the latter vehicle and transmitted to the establishment's ground station. Their orbits are just defferent enough for them to miss each other by inches, so that the rogue's relative velocity changes from twice the orbital velocity approaching the establishment vehicle to twice the orbital velocity going away. The beacon's flashing rate is observed to increase from the rate detected when they are distant from each other, until they pass, and then decrease again to the former rate of flashing. The wavelength of the light, however, gets longer as they approach, and continues to get longer after they pass. Does that make sense?

Spider-Man · 2003-10-01 17:02:44

Not at all. The wavelengths would get shorter and the frequency increase as they approached ? the Doppler effect.

I fail to see how your thought experiment relates to Relativity.

If I haven't already mentioned it, the thought experiment that disproves Relativity uses the theory's own fundamental concepts against it:

There are two astronauts, Jack and Jill, in the vacuum of space, far from any planets or other relative celestial bodies. They have two stories.

Jill's testimony: "I was sitting motionless in the vast emptiness of space. Then suddenly, approaching from far away, I saw Jack in his spacesuit floating towards me. We waved, and he flew by me."

Jack's testimony: "It was a while before Jill showed up, but eventually she did. As I waited for her, not moving, she flew towards me, and waved. Then she drifted passed me, and went away."

These seem contradictory. But according to Einstein, they are not. Both stories are in fact truth. Everything is relative, the good astrophysicist purports, the fundamental principle to relativity.

So, now let's say that Jack and Jill were both carrying clocks. If Jill is the one moving, as Jack insists, then her clock should tick relatively slower to Jack's clock. But if Jack is the one moving, then only his clock should be ticking slower. But both clocks can't be going slower.

So they indeed cannot both be moving! both cannot be right. But the first aspect of Relativity, id est, that everything is relative to everything else, must be true; that's been thoroughly proven. And so has the fact that acceleration (not velocity) causes time dilation.

Think about it.

dicktice · 2003-10-02 11:19:10

Spider:
Sorry, I screwed up again. Don't have time to read your reply, but what I meant to say (if I'd thought it through properly) should have been--

If you're on a mountain at the back of the Moon, and this flashing light probe accelerates towards you the observer due to Moon's gravity at escape velocity just misses you before continuing away at deiishing velocity due to Moon's gravity.... How about that.

One day later, I'm back: Read your thought experiment. Either clock is running slower than the other, that's what one has to grasp. You (the observer) have to exist, for both clocks to run slower. . . relative to you!

Now back to my (restated) thought experiment: You see the rate of the light flashes decrease due to the increasing velocity, until the probe is opposite you, and increasing again as it decelerates going away. The clock in it appears to speed up and then slow down, in other words. Meanwhile, doppler effect causes the wavelength of the light to appear increasingly shorter approaching, longer after passing. Where does that leave me. Gotta go.

dicktice · 2003-10-04 09:46:42

Spider: I edited the just-previous, forgetting that it wouldn't appear as a "New Post," but this should do the trick.

Shaun Barrett · 2003-10-05 04:47:29

Dicktice:-

The clock in it appears to speed up and then slow down, in other words.

I don't think it works quite like that, Dicktice.
The direction of travel doesn't matter as far as time dilation is concerned. Whether someone is travelling from here to Alpha Centauri at 99% the speed of light or doing the same speed coming back, time is just as dilated for that person in either direction. If it weren't so, then the time dilation effect would cancel out and a clock sent on the mission would read the same as a clock left here on Earth, when the spaceship arrived home.
The wavelength of light is affected differently because of the 'crowding' effect as the source approaches and the 'attenuation' effect as it recedes. This is a whole different phenomenon.

Dicktice:-

You (the observer) have to exist, for both clocks to run slower. . .relative to you!

This is the best explanation I've heard yet for this relativity paradox. It clarifies it for me. Nice one, Dick, and thank you!

Pat Galea · 2003-10-05 10:25:35

Einstein is very clear, if you read Relativity, his book on the subject, that it is not velocity, but acceleration which causes time dilation. You can go as fast as you want, but if it's at a constant velocity, you won't experience time dilation anymore than you will experience artificial gravity (G-forces).

Both velocity and gravity cause time dilation. The one caused by velocity (or strictly relative velocity) emerges in Special Relativity. The dilation caused by gravity is shown in General Relativity.

Where acceleration comes in is the resolution of the twin-paradox. If Bill leaves Earth in a space ship travelling at 0.99c, while his twin brother Fred stays at home, then each of them will perceive the other's clock to be running slower than his own. (Note that this has nothing to do with the propagation delay due to the finite speed of light. Even if you take that into account, the time dilation is there.)

This looks like a paradox - how can each clock be running slower than the other? - but it's fine provided each of them continues in their current state, Bill travelling at a constant velocity and Fred sitting at home.

The interesting thing happens when Bill turns round and heads back to Earth. When he arrives back home, Fred has aged more than Bill i.e. Fred's clock has been objectively running faster than Bill's.

This is resolved by the fact that there is an asymmetry between the brothers. Bill has undergone an acceleration (when he turned his ship round) while Fred has not. This asymmetry accounts for the difference in the clocks.

[Pedants may note that there is a slight inaccuracy in my example. Bill has accelerated from Earth at the beginning of the trip, thus generating an immediate asymmetry between the brothers. Technically, we should have Bill on an infinitely long journey extending into the distant past and future, no acceleration and constant velocity, and 'flying by' Earth at 'zero-hour'. However, this complication doesn't significantly affect the thought experiment, so it's usually omitted from it.]

The gravitational time dilation is due to the difference in gravitational potential between two points. So a clock in orbit around the Earth runs slightly faster than one sitting on the surface. This isn't the same dilation as that caused by velocity differences.

[Pedant alert again... superficially it isn't the same case, but if you delve really deeply into relativity, they are sorta kinda the same kinda sorta thing deep down... but hey, let's not go there! ]

Shaun Barrett · 2003-10-05 19:00:33

Hi Pat!
I was wondering how long it would take before you spotted this little discussion and chimed in!

It's good to have your input once again.

It's an interesting discussion, for me at least, because it helps to resolve a few things in my own mind about how relativity works. However, it doesn't take long before you realise a complete understanding of General Relativity is essentially unobtainable unless you have a very high competency level in mathematics.
At least the Special Relativity is a little more accessible!
:;):

Shaun Barrett · 2003-10-05 19:17:29

Incidentally, Pat, have you had much contact with the "Rethinking Relativity" stuff SpiderMan has made reference to in this thread?
It looks thought-provoking from my perspective but, as I've confessed, I don't truly understand relativity in all its glory, so I may be too easy to impress with hocus-pocus and smoke and mirrors!
:laugh:
Is it true that the "ether theory" can explain physical phenomena more completely than relativity? Do we think in terms of gravity travelling at light speed, while actually doing the calculations as though it propagates almost instantaneously? Is Tom Van Flandern crazy or does he have a case? Is it even remotely conceivable that time might be found to be absolute and that Einstein's mathematical masterpiece is in fact a contrived and unnecessary white elephant based on the failure of an experiment (Michelson-Morely) which was never conducted properly anyway?
Should I be worried about such questions .. or should I get out once in a while, have a few beers and loosen up?!!

Free Spirit · 2003-10-05 22:32:26

Should I be worried about such questions .. or should I get out once in a while, have a few beers and loosen up?!!

You should worry about such questions and guzzle a few beers as you do. Beer and insight sometimes go hand in hand. :laugh: But it's good to see that people here have an open mind. People sometimes takes Einstein's work as holy gospel, that he was infallible. But people used to say that about Isaac Newton until some punk clerk came along and shattered much of Newton's theories. I think we're just looking at little pieces of a big picture we can't see in whole yet and thus all of the strange contradictions and quirks that come up in physics.

Shaun Barrett · 2003-10-06 01:22:23

Free Spirit:-

Beer and insight sometimes go hand in hand. :laugh:

I believe this observation is very accurate, though I might be inclined to replace the word 'sometimes' with 'often'.

Many are the gentlemen who, while seemingly unaware of impending difficulties at the beginning of a long evening of philosophical discussion with the boys at the pub, after some hours and several refreshing ales, become gradually and almost miraculously aware of the following insights:-

a) They haven't a clue how relativity works.
b) Their drinking companions haven't a clue about politics.
c) It's much later than they thought.
d) Their wife is in bed.
e) Their dinner is in the dog.
f) And they're in a lot of trouble!!

Which only serves to underline the wisdom of Free Spirit's words, which describe the uncanny ability of beer to clear the head and elevate the human (or at least the human male) consciousness to a higher plane of awareness!

dicktice · 2003-10-07 09:16:56

I just got through reading every post under this topic, and believe if I had done so before blundering into it halfway along, I probably wouldn't have. It's been a wonderful brainstorn-like debate, that remains (so far) open-ended. My own two contributions (made in ignorance of what had gone before) were (1) an observer of two clocks whizzing past in opposite directions would perceive them both to be slow, and (2) an observer on a mountain on the Moon observing a probe with a flashing light accelerating--coming in--would exhibit increasingly rapid flashes, reach a maximum rate--when opposite--and decreasingly rapid flashes as it deccelerates--going away. The wavelength of the flashing light on the other hand would appear shorter, coming in, and longer, going away. The first (flashing rate) effect is symmetrical, while the second (wavelength) effect is assymetrical, with respect to the observer's local time and place. When I concocted this thought experiment (after a couple of false starts) I'd hoped by combining periodicity and wavelength, to improve upon the clock-alone example everyone seems to use. (Perhaps a neon-lit clock would've been more suitable!)
Aside from those offerings, I tend to think that anyone of you who thinks there is an "ether," or that gravity propagates faster than light" is mistaken.
Space-time distortions resulting in "gravity wells" being formed might be likened to standing waves and swells propagating on the ocean, rather than actual quanta migrations, similar (if not the same) to electromgnetic phenonena.
What a great "everthing old is new again" topic this is!

Pat Galea · 2003-10-08 09:59:11

I was wondering how long it would take before you spotted this little discussion and chimed in!

You know, it's always a little scary when someone on a forum says something like this!

I haven't replied before now 'cos a whole batch of Preacher comics arrived from Amazon and, well, some books just need readin'.

(Oh, I managed to sneak into a politics thread somewhere and dump a sarcy comment into the broth. Doesn't count as real interaction; was just letting off steam between books.)

have you had much contact with the "Rethinking Relativity" stuff SpiderMan has made reference to in this thread?

I've read the article, and I have heard of the guy before. It's an interesting controversy.

My take on the whole thing is this:

As far as I know, General Relativity is fine as it is. It's based on a sound principle (that gravity and acceleration are, deep down, the same kinda thing). That gives the whole equivalence between gravitational and inertial mass a "logical basis" (for want of a better phrase). Otherwise it'd be hard to see why they should be the same.

On the other hand, there really is no fundamental reason why GR must be right. There are interesting cracks beginning to appear in the theory. The fact that it even allows the possibility of reverse time-travel gives cause for concern; yes, it may be that no time machine can actually be used (because noise and positive feedback will shut it down as soon as you switch it on). But still, the fact that such solutions of the equations exist is "odd", to say the least.

And it's proving desperately hard to kludge it into a good theory with Quantum Mechanics. QM is pretty much the best scientific theory ever produced. It just works so damn well, everywhere you try it. Yet we need two theories to describe the universe, not just one. How strange!

So I don't think anyone is unprepared for the fact that one or more theories are going to have to at least give a little at some point. Historically, that's always turned out to be the point at which the most fascinating revolution is about to happen; you've almost got it all worked out, but you just need to clear up these pesky details...

As to the "ether" theory...

Well, I can't answer that. Special Relativity works; it gives the right answers. Some people say that it's 'absurd' to imagine that electromagnetic waves can propagate without having a medium to "do the waving". I really can't go that far. How can we tell what is absurd for the universe at the fundamental level? What reason do we have to think that deep down it must behave in a way that is analogous to the things we see at our macro level?

When you push a stone with a stick, you get a kind of image in your mind of what is going on. But when you analyse what is actually happening, it starts to get difficult to say what is really going on at the tiniest level between the stick and the stone. The atoms are hitting each other. Well, not really the atoms, the outer electron shells. Well, they're not really pushing each other, more sort-of excluding other electrons by a combination of quantum effects and electric repulsion. And that's mediated by virtual photons being exchanged. And these photons aren't literally pushing the electrons (for otherwise how would electric attraction work?).

It's so tempting to try to find something deep down which works just like an everyday thing we're familiar with. Like throwing a ball, or pushing with a stick... or a wave on water. But truthfully, it just ain't like that. We don't have the faintest idea what this stuff really is, or what makes it do it. Every so often we get another theory which explains how things work in terms of something at a more fundamental level. This just pushes the same mystery down further, but it's still there. It's beginning to look like we may be reaching the end of these detailed explanations, at least as far as particles are concerned. Or maybe not; watch string theory for exciting developments.

So while we can't analogise fundamental physics to everyday life, we can do the next best thing: we can describe it in exacting detail, using the most phenomenal language ever developed by mankind: mathematics.

Now, math doesn't even attempt to tell you what a thing is, or what it means. It just tells you what it does, or describes its attributes.

Why the universe appears to follow mathematical laws, I have no idea. But I'm convinced that somewhere in it all, something that makes the universe run resembles in some way whatever it is that the math is describing.

Which isn't to say that the universe is mathematical; I once heard a lovely quote to describe this position:

"Just because the Bible can be written in English, it doesn't mean God is an Englishman."

Yup, that's right.

So this is basically my long-winded way of saying that I don't know, and furthermore, I'm not sure we can ever really know, and we have no way of telling what is 'absurd' (unless it generates a bona-fide logical-implosion-type contradiction with reality).

But it's sure as hell fun getting more and more details, learning bit by bit how all the pieces fit together, how we can manipulate them to make them do what we want.

Should I be worried about such questions .. or should I get out once in a while, have a few beers and loosen up?!!

Beer good. Get yourself a copy of A Man, A Can, A Plan. Some great beer recipes in there.

Shaun Barrett · 2003-10-08 19:37:19

Thanks, Pat!
A very nice summary of how you see the situation. Your reference to clearing up those 'pesky details' is so true. Elsewhere, I touched on the 'pesky details' that were annoying physicists about a century ago. Those annoyances eventually led to nuclear physics, Quantum Mechanics and The Standard Model!
I'm very much looking forward to where the present dichotomy between Relativity and Quantum Mechanics will take us. It promises to open all sorts of interesting pathways.

dicktice · 2003-10-09 09:37:15

I'd like to try and "settle" the time dilation due to accelation and/or velocity question, of Shaun/Spiderman. It's possible by means of yet another thought experiment, as follows:

(Open space example) Two spaceships depart together on a flat plane representing space with the time-axis from left to right--one along a straight line and the other along a curved line--and arrive together. The clocks don't match on arrival, with the curved-line clock having run slower than the straight-line clock. Since acceleration was involved, velocity alone can't be attributed to the discrepancy.

(Closed space example) Two spaceships ditto, but on an open-ended cylinder representing space with the cylindrical axis as the time-axis--one along a straight line on the surface and the other along a line spiraling around the cylindrical surface. The clocks don't match on arrival, with the spiral-line clock having run slower than the straight-line clock. But, by imagining the cylinder cut and unrolled, the spiral is seen to be straight as well, only longer. Velocity alone can be attributed to the discrepancy.

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