Time and Gravity

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 33821.  Wed Nov 23, 2005 1:06 pm Good point.

 33829.  Wed Nov 23, 2005 1:20 pm No, it's not, thinking about it. (I had a few minutes to do so as I was ... well ... I wonder how many great discoveries have been made while sitting with nothing else to do on the ... but that's another question.) It must depend on how far apart B & C appear to A, i.e. how far apart they were when they started traveling at the speed of light (from A's perspective). It must be that distance divided by the speed of light much later. At least I think it must, but I'm not sure. Yes, dr.bob, thoroughly confused.

33831.  Wed Nov 23, 2005 1:38 pm

 Rory Gilmore wrote: Notice in the first film the creature was damn near invincible and in the last one, they like shot it with a gun?

They didn't have any guns in the first one, just flame units and a highly technological (not!) cargo net.

33835.  Wed Nov 23, 2005 1:49 pm

 Rory Gilmore wrote: Notice in the first film the creature was damn near invincible and in the last one, they like shot it with a gun?

The last film was set some time after the others so there could conceivably have been some advances in weapons technology.

 33836.  Wed Nov 23, 2005 1:53 pm I thought your point was that C could pass A before A reached B, as the distances weren't specified.

 33842.  Wed Nov 23, 2005 2:08 pm Ah, now that is a good point. (Except that I think you're mixing up A & B. Doesn't B start off in the middle? I.e. A-> B <-C ) So if C is closer to B then B will see C passing first, whereas A (according to the argument I was proposing) will see B pass before C. Now confusion isn't sufficient and I'm going to have to resort to bewilderment.

 33852.  Wed Nov 23, 2005 2:30 pm No, it will see C pass before B. Or general relativity is complete mess. A----------B-----C ---A-------B--C--- ------A---CB------ ------C---AB------ ---C-------B--A--- C----------B-----A

 33870.  Wed Nov 23, 2005 3:15 pm Ah yes, of course. I was thinking that A would not see B and C getting closer together because they were both moving at the speed of light, but of course they are moving toward A. It just shows what thinking about this does to my brain.

 34049.  Thu Nov 24, 2005 7:58 am First of all, I assumed but didn't explicitly state that A, B, and C were equidistant at the start. If C is closer to B then B will indeed see C passing first, whereas A will see B pass before C. It is an effect of relativity that it changes causality. Events that appear to happen in a particular sequence to one observer (B sees C pass before A) will happen in a different sequence to a different observer (A sees B pass before C). So Quaint is right about this one. This does not break the important law of causality since you can't use this to have an effect happen before its own cause, but it does make life very confusing. Remember that A will see B and C both moving towards it at the speed of light. Therefore, from A's point of view, B and C are not moving with respect to each other. This makes sense since, as B and C are moving at the speed of light, their observed time frames will have slowed to a complete stop. Thus, from A's point of view, their time frames are frozen at the moment the experiment starts when they are a distance apart. I'm not sure why Rory thinks that different sequences of events from different viewpoints will make General Relativity a complete mess.

 34116.  Thu Nov 24, 2005 11:57 am So you could set up a camera at either end and they would see different things? Maybe it's the brain that's got it all wrong.

 34417.  Fri Nov 25, 2005 10:55 am What the cameras saw would depend on whether they were stationary with respect to A, B, or C. The whole point about relativity is that all motion is relative and that, in the absence of acceleration, you will always appear stationary to yourself while things appear to move around you. If the cameras at either end were stationary with respect to B, they would see the same thing that B sees. The same applies for A or C.

 34435.  Fri Nov 25, 2005 11:38 am I think I understand now... Thanks.

 36895.  Sun Dec 04, 2005 9:00 am To recap; Steven said, "The further away from gravity you get, the slower time runs, and with no gravity time stops. This was proved by taking an atomic clock up in an airplane and when it landed it was running slightly slower." I said; WRONG! There is no gravity between the stars, if time stopped, how would the light, or anything else, reach us? Although it is true about the airplane it is actually accelerations which have a time dilation effect, the faster you travel, the more slowly time passes for you. If you hitch a lift on a photon (of light) then time for you freezes. I left in the inaccuracey about no gravity between the stars because I wanted to keep the explanation simple. The whole Univere experiences it's own gravity. Although how we explain the accelerating expansion of the universe remains problematic. Many people just don'tbelieve dark energy or dark matter, and feel there must be another explanation which doesn't involve inventing new types of matter, and as for inventing a new type of energy!! There is an axcellent book, "The Elegant Universe" which explains all this complicated if A is travelling towards B and so is C from the opposite direction. I don't have the time to try to remember and regurgitatte that just now - I'm at my brothers helping him "install", not just hang, a back door!! I'd like to see the physicists equations for that!! Black holes were mentioned by other posters. This was another reason against the "time runs slower on Earth because we have more gravity". It is well known that at the event horizon of a black hole time stops. Ergo the closer you are to a gravity well the slower time passes relative to someone outside it.

37029.  Mon Dec 05, 2005 6:54 am

 HarryAlffa wrote: Black holes were mentioned by other posters. This was another reason against the "time runs slower on Earth because we have more gravity". It is well known that at the event horizon of a black hole time stops. Ergo the closer you are to a gravity well the slower time passes relative to someone outside it.

So "the closer you are to a gravity well the slower time passes relative to someone outside it." How does this contradict "time runs slower on Earth because we have more gravity"?

Surely Black Holes are a proof that "time runs slower on Earth because we have more gravity".

 56618.  Thu Mar 02, 2006 3:12 pm Dr Bob; Yes, absoloutely correct and is what I've been saying since I started this thread!! My mistake! I wrote exactly the oppposite of what had been posted previously and posited by Stephen. The wrong thing to say is "time runs quicker on Earth because we have more gravity". Time runs slower on earth than off planet, out of Earths gravity well.

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