Time is relative / Relativity / etc.

[Tensorman]

Firstly, I don't believe in that "time is relative" crap.

That's no crap, but solid science. It has been experimentally verified many times. Belief has nothing to do with it.

[DragonMaci]

That's no crap, but solid science. It has been experimentally verified many times. Belief has nothing to do with it.

The only so-called verification I've heard of is experiements where clocks slowed down. That isn't verification. It could just mean that the mechanisims on the clock slowed down.

Either way, you are wrong that belief has nothing to do with it. You have to choose whether or not to believe in facts and so-called facts (leaving aside for know which time being relative is), so belief has everything to do with it.

But most importantly, do you seriously expect me to be convinced by your statement when you offer nothing to back it up?

[brian0918]

Firstly, I don't believe in that "time is relative" crap.

Laughable. If you are using a cell phone or a GPS device, you believe in that crap. Without Einsteinian relativity, those things would not hold their orbits for long.

Secondly, the crew do need to get back "in time." The CSE-100 Dragon is a science vessel so it needs to get back to its parent company in the lifetime of its current owners. Thirdly, I don't see any reason to think Einstein was right on the speed of light being an absolute.

Not an absolute. Just an upper limit on the acceleration of matter.

Edited February 11, 2008 by brian0918

[DragonMaci]

Laughable. If you are using a cell phone or a GPS device, you believe in that crap. Without Einsteinian relativity, those things would not hold their orbits for long.

I never said I don't believe his theory of gravity.

Not an absolute. Just an upper limit on the acceleration of matter.

That is what I am sceptical about.

[Steve D'Ippolito]

The only so-called verification I've heard of is experiements where clocks slowed down. That isn't verification. It could just mean that the mechanisims on the clock slowed down.

Also radioactive particles such as muons formed in the upper atmosphere when cosmic rays bite the big one up there somehow manage to last long enough to get to the surface. At rest their half lives aren't nearly long enough.

It's not a matter of GPS keeping in orbit, BTW, it's a matter of keeping the clocks in synch. THey have to correct for relativistic effect.

[Drew1776]

Also radioactive particles such as muons formed in the upper atmosphere when cosmic rays bite the big one up there somehow manage to last long enough to get to the surface. At rest their half lives aren't nearly long enough.

It's not a matter of GPS keeping in orbit, BTW, it's a matter of keeping the clocks in synch. THey have to correct for relativistic effect.

Could you elaborate on the second statement? I haven't heard of this before. Bear in mind I'm ignorant of how GPS keeps time.

Edited February 11, 2008 by Drew1776

[D'kian]

Could you elaborate on the second statement? I haven't heard of this before. Bear in mind I'm ignorant of how GPS keeps time.

As far as I know GPS sats keep time with an atomic clock (one clock per satellite). Such clocks are very accurate and can measure smaller fractions of time than regular clocks, therefore they are more easily affected by relativistic effects.

[Adrian Hester]

The only so-called verification I've heard of is experiements where clocks slowed down. That isn't verification. It could just mean that the mechanisims on the clock slowed down.

It was an atomic clock (or, rather, four of them in the original experiment), not a mechanical clock--it measures time essentially by counting atomic vibrations, not clicks of a hand.

[agrippa1]

The only so-called verification I've heard of is experiements where clocks slowed down. That isn't verification. It could just mean that the mechanisims on the clock slowed down.

Well, yeah, you're right, it might just be that the "mechanism on the clock" slowed down. The mechanism in question, in atomic clocks, is the frequency of radiation associated with the transition between two energy levels of a specific Cesium isotope. But every "mechanism" tested shows exactly the same frequency change, due to gravity (for general relativity effects) and velocity (for special relativity effects). You can argue that only the mechanism slows down, and that "time" stays the same. The evidence is pretty strong that your bodily functions will also slow down, that your neurological activity mechanism will also slow down, etc. So you could maintain stubbornly that all mechanisms slow down, but that "time" does not. But then you would be left with an impractical and objectively immeasurable concept called "time." The choice, I suppose, is yours, but since most humans define time in terms of measurements of time, and since we've agreed to define measurement of time in terms of the frequency of radiation associated with the transition between two energy levels in the ground state of Ce133, it would probably behoove you to join the rest of mankind and accept that "time" slows down under relativistic effects, and that it is thus "relative."

Edit: mixed up special and general relativity.

Edited February 11, 2008 by agrippa1

[mrocktor]

What is "time"? How is "the mechanism of the clock slowed down" different from "time slowed down"? You must be measuring the mechanism by some reference, what is it? Answering those questions would make your objection more clear DragonMaci.

[Tensorman]

Could you elaborate on the second statement? I haven't heard of this before. Bear in mind I'm ignorant of how GPS keeps time.

There are two contrary effects: time in the GPS satellites runs slower (than on earth) while they move relative to the Earth (the well-known time dilation), and it runs faster while gravity up there is weaker. The clocks must be corrected for the combined effect (the gravity component dominates); with the calculated correction they work fine. See for example here.

[brian0918]

The evidence is pretty strong that your bodily functions will also slow down, that your neurological activity mechanism will also slow down, etc. So you could maintain stubbornly that all mechanisms slow down, but that "time" does not.

It would not slow down from your perspective, only from an outside observers perspective. You would also see their biological functions slowing down as well. This is the twin paradox and it is resolved with the introduction of acceleration in general relativity.

Reply to thread:

Please stop this nonsense. GPS satellites, atomic clocks, particle accelerators, anything operating at extremely high speeds or utilizing extremely small increments of time experiences this effect. Einstein used this "time is relative crap" to predict the precession of the perihelion of Mercury, which was a centuries-old problem with Newtonian motion.

On a side note, it is pretty easy to travel into the Earth's future. You could go up on a plane, fly around for a few hours/days/weeks, come back down, and you would be in everyone else's future - only by a tiny fraction of a second, however.

Here is a quick layman article describing the use of special/general relativity (ie, "time is relative crap") to keep planes in the air and GPS satellites in orbit.

Edited February 11, 2008 by brian0918

[DavidOdden]

Moderator's note: the concept "insult" refers inter alios to acts such as saying that someone is talking nonsense, crap, or getting their information from a kid's book. You may recall that we've not totally down with insults. If someone is in fact spewing provable nonsense, then calling an idiot an idiot is a recognition of reality, but you need to support your accusation of idiocy. Argue the science and drop the vacuous insults.

[brian0918]

Einstein's relativity (def: theory stating that all motion must be defined relative to a frame of reference and that space and time are relative, rather than absolute concepts) is fundamental to both special AND general relativity.

Special relativity (which the layperson more often associates with the phrase "time is relative") is simply general relativity in the special case of a universe without gravity.

It makes absolutely no sense to say you believe his "theory of gravity" without believing his theory of relativity, since the relativity of time and space is precisely what differentiates his theory of gravity from Newton's theory of gravity.

Edited February 11, 2008 by brian0918

[D'kian]

Einstein used this "time is relative crap" to predict the precession of the perihelion of Mercury, which was a centuries-old problem with Newtonian motion.

As I understand it, the Mercury problem was solved by Einstein, but using the matter/energy equivalence aspect of his theories, rather than the relative rate of passage of time (although I assume that has some effect as well considering the size of the Sun's gravitational field).

On a side note, it is pretty easy to travel into the Earth's future. You could go up on a plane, fly around for a few hours/days/weeks, come back down, and you would be in everyone else's future - only by a tiny fraction of a second, however.

And you'd need a very accurate clock capable of measuring very tiny intervals of time.

While I like to imagine some form of FTL travel when reading and writing SF, I'm almost entirely certain that c is the speed limit for this Universe. I expect in the future we'll learn how to travel as close to it as possible, too, and that will generate all sorts of issues between interstellar travelers and stay-at-homes (especiallly if we also develop longer lifespans).

[Tensorman]

As I understand it, the Mercury problem was solved by Einstein, but using the matter/energy equivalence aspect of his theories, rather than the relative rate of passage of time (although I assume that has some effect as well considering the size of the Sun's gravitational field).

The prediction of the Mercury perihelion precession (that is: the part that cannot be explained by Newtonian mechanics) follows from Einstein's field equations, i.e. his gravitational theory, in particular from the Schwarzschild solution for a spherical symmetric field around a star. But as Brian0918 remarked, the special theory with its time dilation and matter/energy equivalence is a special case of the general theory, you cannot accept general relativity without special relativity, a confirmation of the general theory is indirectly also a confirmation of the special theory.

[brian0918]

As I understand it, the Mercury problem was solved by Einstein, but using the matter/energy equivalence aspect of his theories, rather than the relative rate of passage of time (although I assume that has some effect as well considering the size of the Sun's gravitational field).

Einstein used the equivalence of gravity to the curvature of spacetime (which comes out of general relativity) to solve the problem, which all rests on the theory of the relativity of space and time. This paper is a good introduction to the problem, and actually derives the equations for this specific problem.

I only took one course on general relativity, and it was completely disconnected from Newton's theory, but I think the source of the difference between Newton's and Einstein's answers is that Newton assumed that gravity was instantaneous, ie, if two objects are moving, at time t, object A will will feel the effect of gravitational attraction from object B's position also at time t. Another way of saying it is that Newton assumed gravity moved at infinite speed.

However, because this gravitational attraction also moves at the speed of light, object A at time t is actually attracted by the position of object B in the past (object B's past, that is). How far in the past? Well, some amount related to the distance between A and B.

Edited February 12, 2008 by brian0918

[agrippa1]

On a side note, it is pretty easy to travel into the Earth's future. You could go up on a plane, fly around for a few hours/days/weeks, come back down, and you would be in everyone else's future - only by a tiny fraction of a second, however.

Hmmm... I just tried an experiment. I left my office and walked around the parking lot really fast. When I got back, I asked my office mate how long I'd been gone. Sure enough, I had traveled five minutes into his future!!!

[D'kian]

Thank you both.

I only took one course on general relativity, and it was completely disconnected from Newton's theory, but I think the source of the difference between Newton's and Einstein's answers is that Newton assumed that gravity was instantaneous,

The way Asimov tells the story, Newton did not, and could not, take into account the fact that the Sun's gravitational field, made up of energy, had a mass of its own, which generated further gravity (that is, matter and energy both ahve mass, but only the raw mass of the Sun was taken into account when applying Newton's theories). this, of course, is a layman's explanation, highly simplified.

Asimov goes on to explain the astronomers of the XIX century simply assumed there was an aditional mass inside Mercury's orbit, which had gone undetected. A small planet or large asteroid (not unreasonable, seeing how difficult Mercury is to spot at all). This hypothetical body was named Vulcan, after the Roman god of the forge. Of course it was never found because it was never there.

But the foremost proponent of the existence of Vulcan was a man named Leverrier, who had used Newton's laws to discover Neptune by the perturbations it produced in the orbit of Uranus. Naturally he held Newton's work to be completely valid (it is, albeit not complete) and naturally he expected to find a physical body nearer the Sun. I believe he even calculated its orbit. He must have been bitterly disappointed when it failed to show up.

[KendallJ]

There are many discussions of quantum mechanics on this board, and at least a historical summary of some Objectivist physicists thinking on the subject here:

http://armchairintellectual.blogspot.com/2...-my-recent.html

My understanding of the concern with relativity is it's rationalistic start at assuming c constant. David Harriman in his course The Philosophical Corruption of Physics discusses this. The idea is that one does not assume the beginning and then because the math seems to be predictive assert the assumption must be true. The mathematics of relativity could just as easily be derived if you assumed that what was different was not the assumption about c, but he assumption about Newtonian conservation of momentum. While the maths end up the same, it has profound implications for what is actually occurring in reality. And as of yet, specific time dilation and length contraction have not been shown independent of relativistic momentum. As long as that is he case, then the conclusion that time dilation and length contraction exist, is circular, it still assumes the starting assumption.

I'm not a QM nor relativity expert, and I wish the late Stephen Speicher was still here as he'd have a few things to say about it.

[Adrian Hester]

My understanding of the concern with relativity is it's rationalistic start at assuming c constant.

In fact, Einstein started with Maxwell's equations and showed that combined with certain experimental facts they yielded the Lorentz transformation equations that imply that c is constant in all inertial reference frames.

David Harriman in his course The Philosophical Corruption of Physics discusses this. The idea is that one does not assume the beginning and then because the math seems to be predictive assert the assumption must be true. The mathematics of relativity could just as easily be derived if you assumed that what was different was not the assumption about c, but he assumption about Newtonian conservation of momentum. While the maths end up the same, it has profound implications for what is actually occurring in reality.

Not really. The simplest statement that permits special relativity to be derived, and one of the results that automatically follows in any equivalent system regardless of your starting point, is that c is constant in all inertial reference frames. This is true regardless of the starting point (Maxwell's equations or the relativistic transformation of momentum, the latter being a much less natural place to start--indeed, it seems to me like something you'd start with only if you knew the final result and wanted a different derivation that revealed something more clearly about mechanics), and whether you start with it to derive your equations (the usual method in introducing special relativity to students, since it makes for by far the most natural and philosophically basic introduction to problems of simultaneity) or derive it in turn from a different starting point (as in fact Einstein did from Maxwell's equations), it is still an ineluctable consequence of special relativity.

And as of yet, specific time dilation and length contraction have not been shown independent of relativistic momentum. As long as that is he case, then the conclusion that time dilation and length contraction exist, is circular, it still assumes the starting assumption.

But relativistic momentum implies time dilation and length contraction and vice versa in the same way that 1+1=2 implies 5+7=12 and vice versa, or that the various statements of Newtonian mechanics imply each other. The very fact that time dilation, length contraction, and relativistic momentum occur together like that supports another consequence of the same equations, the constancy of c. It would only be if they didn't co-occur that you'd have something to write home (or a physics journal) about.

I'm not a QM nor relativity expert, and I wish the late Stephen Speicher was still here as he'd have a few things to say about it.

I thought Speicher was sharply critical of Harriman's comments on relativity theory. I mean really critical.

[KendallJ]

I thought Speicher was sharply critical of Harriman's comments on relativity theory. I mean really critical.

'

He also continued to support Little's TEW after Harriman renegged on it. Maybe if you can link us to his statements we can get his opinion from the grave...

[KendallJ]

Look I"m not trying to argue a particular view, but rather that the "you should just accept it because the world has" is nothing more than balatant argumentum ad veracundia.

[adrock3215]

From my understanding physics is concerned with establishing theory which can predict observed phenomena accurately. It does not attempt to prescribe any kind of ultimate truth. Relativity is just that - a theory which describes various observed phenomena from relative viewpoints; it says nothing about the true nature of the world.

[Adrian Hester]

He also continued to support Little's TEW after Harriman renegged on it. Maybe if you can link us to his statements we can get his opinion from the grave...

I looked for them but not too assiduously and couldn't find them. They're in one of the threads over on the Speichers' forum, I think. (Or else here somewhere. I don't think it would have been any other place.)

Look I"m not trying to argue a particular view, but rather that the "you should just accept it because the world has" is nothing more than balatant argumentum ad veracundia.

No worry--I just assumed you were summarizing Harriman's arguments and I was just responding to them as you presented them; I haven't read it (heard it?) myself.