I've read that article - it was pretty hard as my native language is not english, I am not accustomed with physics terms in english and my physics knowledge is pretty limited to high-school level.

I'm curios of some things, if you can tell me:
1. where did Einstein (I guess it was Einstein) said that this effect should be expected? (just curios, and curios about some more details about it, if I can look upon that)

2. isn't the "time" (as an entity) something hard to really imagine? I mean, if we imagine something like a god (for the sake of explanation) - invisible and who cannot touch objects or have any other effect upon the universe, perhaps omnipresent or something (just to be big and be able to watch everything happening), and sees the entire universe all at once, doesn't that mean that there would also be a 'global' time? Also, if we also imagine a 'time' that represents the order of events, shouldn't it really exist, and if it does, wouldn't it differ significantly from the "local time"? or how can you tell that two things happen at once, yet one after another?

3. The experiment didn't prove that time is indeed an entity - perhaps the most obvious way to do it is if one goes in space and returns after 1000 years but he's still young, or he returns on earth and sees the most evolved creatures being the apes (though in this latter case he may wonder if a 3rd world war happened ) of if a time portal would be created, but in this case, teleporting people in past may be very dangerous (a little event may have grave significances after 1000 years, and so, many people of the future would disappear)

By the way, doesn't the teleporting through time imply another "time"? i.e. the first time he traveled in that moment, the second time he teleported in that moment. And, for instance, if someone of the year 2500 would teleport in 2011 and appear on news everywhere and tell the world, should that happen now or after we reach 2500? (year 2500 when he is teleported, so that the universe would 're-start' from the year 2011)

Quote:The precession of a gyroscope in the gravitation field of a rotating body had never been measured before GP-B. While the results support Einstein, this didn’t have to be the case. Physicists will never cease testing their basic theories, out of curiosity that new physics could exist beyond the “accepted” picture.

Yeah, perhaps this current theory would be changed once. But we can't tell, and unfortunately (in a manner of speaking, unfortunately) we don't live a thousand of years to watch if this scientific theory will ever be changed or ever be dismissed.

(June 7, 2011 at 6:15 pm)Zenith Wrote: 1. where did Einstein (I guess it was Einstein) said that this effect should be expected?

Lense and Thirring predicted it, quite early in the development of general relativity. Here's Thirring's paper on the topic. It's rather math heavy, so you're not comfortable with that, you're perhaps best just skipping to the last page with the discussion of centrifugal/coriolis forces.

(June 7, 2011 at 6:15 pm)Zenith Wrote: Also, if we also imagine a 'time' that represents the order of events, shouldn't it really exist, and if it does, wouldn't it differ significantly from the "local time"? or how can you tell that two things happen at once, yet one after another?

Not quite sure what you mean here...

(June 7, 2011 at 6:15 pm)Zenith Wrote: 3. The experiment didn't prove that time is indeed an entity - perhaps the most obvious way to do it is if one goes in space and returns after 1000 years but he's still young, or he returns on earth and sees the most evolved creatures being the apes (though in this latter case he may wonder if a 3rd world war happened ) of if a time portal would be created, but in this case, teleporting people in past may be very dangerous (a little event may have grave significances after 1000 years, and so, many people of the future would disappear)

By the way, doesn't the teleporting through time imply another "time"? i.e. the first time he traveled in that moment, the second time he teleported in that moment. And, for instance, if someone of the year 2500 would teleport in 2011 and appear on news everywhere and tell the world, should that happen now or after we reach 2500? (year 2500 when he is teleported, so that the universe would 're-start' from the year 2011)

Indeed, such paradoxes are the reason that most physicists think that time travel is not possible.

(June 9, 2011 at 11:43 am)lilphil1989 Wrote:

(June 7, 2011 at 6:15 pm)Zenith Wrote: Also, if we also imagine a 'time' that represents the order of events, shouldn't it really exist, and if it does, wouldn't it differ significantly from the "local time"? or how can you tell that two things happen at once, yet one after another?

Not quite sure what you mean here...

I mean... if we have local times, can't it be a global time too (which should be = the order of events).
If all the universe exists "at the same time", doesn't that imply a global time?

And if we have an order of events (i.e. a global time), then two events may happen at the same time (according to this global time). But according to the local times (i.e. here 1 second = there 1 year, and stuff like that) they may happen one after another. Isn't this a paradox?

it's regarding that thing with the omnipresent god I tried to explain, you know, to try to imagine a global time.

P.S. thanks for the link. I'll take a look on it.

Quote:I mean... if we have local times, can't it be a global time too (which should be = the order of events).
If all the universe exists "at the same time", doesn't that imply a global time?

Having an order of events is not the same as having a global time.
A concrete example: An observer on Earth sees events in the same order as observer sitting on a GPS satellite. However, the Earth observer sees the clock on the satellite running at a different speed to his wristwatch due to gravitational time dilation (and the GPS system has an algorithm built in which corrects for this effect).
So whilst events are in a well-defined order, there is no global time.

Quote:And if we have an order of events (i.e. a global time), then two events may happen at the same time (according to this global time). But according to the local times (i.e. here 1 second = there 1 year, and stuff like that) they may happen one after another. Isn't this a paradox?

Actually that's exactly what happens. It's called the relativity of simultaneity. If I see two events as simultaneous, then someone in motion with respect to me will not. Of course, for it to be a noticable effect, the speed has to be large. Indeed, the whole reason we were satisfied with the idea of absolute simultaneity for so long is that we live at very low speeds!

Quote:it's regarding that thing with the omnipresent god I tried to explain, you know, to try to imagine a global time.

You may as well try to imagine invisible pink unicorns . Global time is not compatible with relativity.

(June 9, 2011 at 12:14 pm)lilphil1989 Wrote: You may as well try to imagine invisible pink unicorns . Global time is not compatible with relativity.

Actually, I don't think I could: the invisible pink unicorns are not omnipresent.

Quote:If I see two events as simultaneous, then someone in motion with respect to me will not.

And that was the fact with the omnipresence that mattered: if two observers see two event A, and B, differently (e.g. one sees it B before A, the other sees A and B in the same time), then an omnipresent being 'notices' the 'correct' order of the events, because he doesn't 'look' from a distance to the event, and is not moving at all. And if we have a 'correct' order of events - from 'someone' who doesn't 'look' from a distance and is not moving at all - then that is a global time. If the logic is correct so far, then it means that even if the omnipresent being does not exist, this 'global time' should exist.

The thing you have explained with the observers sounds something like a "subjective view". And the reason I inserted that omnipresent being was in an attempt to explain an "objective view". I hope you understand what I'm talking about.

As about two events happening simultaneously: imagine the universe scaled so that you would see it all, in front of you (now you see the things objectively), and you see two specific stars at the same time, and one star dies, and after that the other one dies. How do you imagine those two stars in two different local times, dying in the same time, yet one after another? You know, if you regard it objectively, then it sounds like this: you have a box filled with objects (cubes, balls, etc.). And one comes and tells you: these objects in the box do not exist in the same time - they only exist in local times.

Quote:and the GPS system has an algorithm built in which corrects for this effect

Can you please give me some more info about this?

Quote:And that was the fact with the omnipresence that mattered: if two observers see two event A, and B, differently (e.g. one sees it B before A, the other sees A and B in the same time), then an omnipresent being 'notices' the 'correct' order of the events, because he doesn't 'look' from a distance to the event, and is not moving at all. And if we have a 'correct' order of events - from 'someone' who doesn't 'look' from a distance and is not moving at all - then that is a global time. If the logic is correct so far, then it means that even if the omnipresent being does not exist, this 'global time' should exist.

As soon as you say that the observer is not moving, you have implicitly chosen a specific inertial frame which is at rest with respect to some object, or set of objects. This choice defines your definition of simultaneity, which is in no way global, since it holds only in your chosen frame.

Quote:The thing you have explained with the observers sounds something like a "subjective view". And the reason I inserted that omnipresent being was in an attempt to explain an "objective view". I hope you understand what I'm talking about.

I do understand. But the existence of such an objective view is entirely uncompatible with relativity. And since relativity correctly predicts the outcome of experiments, it seems to be a good description of the way the universe works, and the lack of an objective definition of time seems to be the way it really is.

Quote:As about two events happening simultaneously: imagine the universe scaled so that you would see it all, in front of you (now you see the things objectively), and you see two specific stars at the same time, and one star dies, and after that the other one dies. How do you imagine those two stars in two different local times, dying in the same time, yet one after another?

Now imagine I ran away from the scaled universe rather quickly. In my rest frame, the events would no longer be simultaneous. That's the key point, your definition of simultaneity depends entirely on your state of motion.



Here's the Wikipedia article on the relativistic corrections for GPS.

Your wiki article hurt my brain after a night of no sleep, workng on audio EQ and CSS. I quit.