| From: Jonathan | 22/06/99
22:19:45 |
| Subject: Time slowing as velocity -> C | post id:
19089 |
| Hi, Something Karl and his guest said last week on the show has been bugging me like hell. He said that as you get closer to a black hole and/or the speed of light, time slows down. Seems easy to imagine and simple enough, doesn't it? That is, until you THINK about it. Time itself may slow down, but no-one would ever know about it. I am talking about this in theory AND in practice! What I am saying is that the statement about time slowing down gives people the impression that they could look at their wristwatch for half an hour and in all that time, see it advance only one second, which is of course, ridiculous or at least, counter intuitive (I accept that all this stuff about special relativity is a bit counter intuitive but I still propose the above scenario to be bogus in the extreme). Just ask yourself the question "how long does time slow down for?" or "how long would you have to wait for your watch to advance by one second"? and you can see this is completely paradoxical. It's like running some movie film on half speed and suggesting that the people in the movie would be aware that they are doing everything in slow motion. What I am proposing is as follows: It would be impossible for a human to perceive or measure time slowing down even if it were possible to accelerate to close to C or if you could get close to a black hole. Since we exist in the fabric of space-time, any "stretching of the fabric", so to speak, could not be seen from a reference point distinct from that fabric. Your watch is NOT time itself. So ALL activity would slow down and eventually stop. Just as your watch would stop, the same forces would surely dictate that YOU would stop too, leaving yourself more or less in a state of suspended animation. Does anyone have any comments about this? I know I'd never get through on the phones on Thursday and if I sent it to Karl he'd reply with his standard response "hey, thanks alot for your interesting comments - why don't you put them on the net so everyone can see them?" and he wouldn't make any reference to them on the show. | |
| From: Dr. Ed G (Avatar) | 22/06/99
22:58:54 |
| Subject: re: Time slowing as velocity -> C | post id:
19094 |
| Yes, that's exactly right. What
they mean when they say time slows down as you approach a black hole or
the speed of light is relative to an observer that wasn't near a black
hole or who had not accelerated to close to the speed of light. As you
say, the speed of light, the rate of an atomic clock, and the
physiological senses that perceive time would all appear completely normal
in the near black hole/close to speed of light frame of
reference. Soupie twist, Ed G.  | |
| From: James Richmond (Avatar) | 23/06/99
12:11:12 |
| Subject: re: Time slowing as velocity -> C | post id:
19135 |
| Jonathan: You said What I am saying is that the statement about time slowing down gives people the impression that they could look at their wristwatch for half an hour and in all that time, see it advance only one second, which is of course, ridiculous or at least... You are quite right. Time always moves at the "normal" rate in an observer's own frame of reference. A person cannot look at their own watch for half an hour and see it advance one second. But a person CAN look at someone else's watch for half an hour (as timed by their own watch) and see the other person's watch advance only one second. For this to happen, the second person would either have to be travelling at high speed relative to the first person or to be in a significantly higher gravitational field than the first person. legolas: Time dilation is a direct consequence of a couple of simple assumptions on which the whole theory of relativity is built: 1. The laws of physics have the same form in all inertial reference frames. 2. The speed of light is constant. We don't have to drop things into black holes to verify time dilation. We can test (and have tested) the effect on Earth. The observable gravitational effects are smaller than they would be for a black hole, but the difference is only in quantity, not quality. The theory of relativity has stood up amazingly well to all kinds of experimental test, so it seems reasonable to extrapolate to situations which can't be tested directly. slowing down time does not slow down a watch, you would need to slow down the mechanics for that. Time dilation effects everything equally - watches, atoms, people, mechanics. JR | |
| From: Geoff P | 23/06/99
13:04:22 |
| Subject: re: Time slowing as velocity -> C | post id:
19153 |
| Yes, to elaborate on James'
comments. Experiments have been performed where two atomic clocks are
synchronised, one is taken on a plane and the other is kept on the ground.
When the two are compared again (on the ground), there is a discrepancy.
This is not due to any mistakes in the clocks but due to time dilation.
The effect is small, but since we can measure time to 1 part in 10^15,
quite measurable. Anyone in the plane with one clock or one the ground
with the other would have seen no discrepancy in "their" clock, it is
simply the time on one clock measured relative to the time on the
other. Only one problem - can anyone tell me whether the time dilation in this experiment was gravitational or due to the relative velocity of the observers? Which is the dominant effect? | |
| From: James Richmond (Avatar) | 23/06/99
14:21:53 |
| Subject: re: Time slowing as velocity -> C | post id:
19191 |
| Both effects contribute to the
clock-in-the-plane experiment. The dominant one is gravitational time
dilation. I think Chris (Avatar) posted a mathematical analysis of this in
an earlier thread. JR | |
| From: Chris W (Plebeian) | 23/06/99
14:37:06 |
| Subject: re: Time slowing as velocity -> C | post id:
19210 |
| The effects are vitally important
to the Global
Positioning System (GPS), which would be desperately inaccurate if
corrections weren't built in. | |