04-15-2008, 01:01 PM
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#76
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I Live Here
Join Date: Feb 2005
Posts: 23,211
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Quote:
CycloneRanger wrote
No! Don't make this mistake!
The situation you have described has nothing whatsoever to do with the twin paradox, with time dilation, or with general relativity. By your analysis, the twin who left would appear to age rapidly if he returned to the Earth, arriving at the same age as his Terran twin. Relativistic time dilation, on the other hand, is very much real, and predicts that the twin who traveled at a significant fraction of lightspeed will have aged less when he returns. His clock is observed to tick more slowly (from our perspective) regardless of which direction he flies—toward us, away from us, whatever.
I suggest you read the Wikipedia article on time dilation—it is absolutely not what you are describing. In fact, you have not taken time dilation into account in your description, which is an error because you have assumed the twin leaves with a significant velocity relative to c.
The twin paradox also has nothing whatever to do with Stern's seeming paradox. In fact, Stern's argument (and its flaws) have nothing whatever to do with relativity, and would be equally (in)valid when applied to, say, communication by sound waves between two moving cars.
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For all of its presumed faults, my paradox would apply if communication was by pony express.
"Those who most loudly proclaim their honesty are least likely to possess it."
"Atheism: rejecting all absurdity." S.H.
"Reality, the God alternative"
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04-15-2008, 02:50 PM
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#77
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Guest
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Quote:
Sternwallow wrote
I'll try.
The image of my grandmother (age 80 today, happy birthday, Grams) took 20 years to reach me. If the image were traveling across space, not just in time, I would deduce that she was 20 LY away when she was 60. But, I know that she was moving away from me at some (say, constant) velocity all her life, at one point (80 years ago) being born right here where I am standing, though I wasn't born yet.
So her image now shows her 20 years younger. It should have arrived here some time ago.
Gran is traveling at 1/3 LY per year because she is 20 LY away at age 60.
She has been continuously visible all these years. In the first second, her image arrived here 1/3 light-second younger than the arrival time.
At 30 she was 10LY away, the image took 10 years and she looked 30, 40 years ago. This is why, when we want to check Gran's age and progress, we can't find her at the calculated distance. The image of her that is younger arrived before now, as it has ever since her trip began 80 years ago.
Sorry, I tire of this. Let's leave it as one of God's holy mysteries, not to be solved by mortals.
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I rather not...
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04-15-2008, 07:35 PM
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#78
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Guest
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Quote:
VladTheImpaler wrote
OK, this grandmother example was extremely difficult to follow, almost incoherent to my mind.
I think you are unnecessarily making things difficult for your self here Stern. Did you read my last reply?
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How was it incoherent?!
You are basically observing the image of a galaxy when it reaches the earth. Not the actual present state of the galaxy itself.
That's why i compared it to a photograph, It is a somewhat "still" image of the past, not the present/future.
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04-16-2008, 12:56 AM
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#79
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Obsessed Member
Join Date: Mar 2006
Location: Norway
Posts: 1,347
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Quote:
CycloneRanger wrote
The situation you have described has nothing whatsoever to do with the twin paradox, with time dilation, or with general relativity.
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Yar, I know. I was not really trying to show that there was a paradox; I didn’t see a paradox with Stern’s examples so I tried to provide an easy example in relation to that. I know I left out the possibility of time dilation, I did so intentionally. Not that I would have been mathematically capable of including it even if I wanted too. I forgot to mention this though.
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04-16-2008, 12:59 AM
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#80
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Obsessed Member
Join Date: Mar 2006
Location: Norway
Posts: 1,347
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Quote:
Desillusioned wrote
How was it incoherent?!
You are basically observing the image of a galaxy when it reaches the earth. Not the actual present state of the galaxy itself.
That's why i compared it to a photograph, It is a somewhat "still" image of the past, not the present/future.
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I was referring to Stern's grandma example, really... and that took me a while to really get what he was saying (i.e. having a tough time understanding that there was a problem in the first place). But I got there eventually (I think). Didn’t have a problem with your explanation.
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04-16-2008, 01:06 AM
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#81
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Obsessed Member
Join Date: Mar 2006
Location: Norway
Posts: 1,347
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Following this thought experiment I really started to wonder about how we would observe an object travelling away from us at a very high speed.
Let’s go back to my earlier example where a spaceship leaves Earth at 50% the speed of light. For the sake of argument let us say that this spaceship is made entirely out of a transparent material and that on Earth we now have immensely powerful telescopes.
As the spaceship gets farther and farther away how would we observe the light, arriving at Earth, of the human interaction on the spaceship when looking through the telescope? Would we as the spaceship got further and further away from Earth start seeing the human interaction on the spaceship as slowing down considerably? Is it as if light gets stretched out?
Eh?
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04-16-2008, 05:23 PM
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#82
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I Live Here
Join Date: Feb 2005
Posts: 23,211
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Quote:
VladTheImpaler wrote
Following this thought experiment I really started to wonder about how we would observe an object travelling away from us at a very high speed.
Let’s go back to my earlier example where a spaceship leaves Earth at 50% the speed of light. For the sake of argument let us say that this spaceship is made entirely out of a transparent material and that on Earth we now have immensely powerful telescopes.
As the spaceship gets farther and farther away how would we observe the light, arriving at Earth, of the human interaction on the spaceship when looking through the telescope? Would we as the spaceship got further and further away from Earth start seeing the human interaction on the spaceship as slowing down considerably? Is it as if light gets stretched out?
Eh?
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Sounds like ordinary time dilation to me.
"Those who most loudly proclaim their honesty are least likely to possess it."
"Atheism: rejecting all absurdity." S.H.
"Reality, the God alternative"
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04-17-2008, 01:16 AM
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#83
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Obsessed Member
Join Date: Mar 2006
Location: Norway
Posts: 1,347
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So that's how it would really look to us?
When astronomers observe stars moving around for instance a super massive black hole that is moving away from us at considerable percentage of the speed of light, do they account for this time dilation considering that the stars will appear to move a lot slower than they really are?
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04-17-2008, 02:45 AM
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#84
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Obsessed Member
Join Date: Oct 2005
Location: Oxford, UK.
Posts: 2,330
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It's more the other way round. They don't actually observe the motion as such, they calculate it from the red shift - the amount that the light is stretched out - so yes, it is taken into account I suppose.
At this stage I would point you at this which is a pretty good and readable layman's account and I think will answer a lot of your questions.
"You care for nothing but shooting, dogs and rat-catching, and will be a disgrace to yourself and all your family"
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04-17-2008, 07:04 AM
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#85
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Obsessed Member
Join Date: Mar 2006
Location: Norway
Posts: 1,347
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Thanks!
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