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BigPapaSmurf
SFN Die Hard
3192 Posts |
 Posted - 12/16/2008 : 07:11:17
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So as I understand it, poorly, the idea goes something like this...
Im moving away from earth at an accelerating rate and I look back at the clock on Earth, as I move faster the photons reflecting off the clock take longer to reach me, thus giving the impression that time is slowing down for me. As I approach the speed of light the clock comes alomst to a halt...
Now the popular version of this goes that when I get back to Earth my twin will be older than I, but if I turned around and returned to earth at any speed wouldnt the clock appear to move faster until I reached earth? The photons received by my eyes from the clock should increase should they not if I am moving towards them?
I seem to remember Einstein saying this was a pointless thought experiment and it was taken too literally by the media.
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"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Dr. Mabuse
Septic Fiend
Sweden
9687 Posts |
Posted - 12/16/2008 : 07:55:14 [Permalink]
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You're not accounting for the relativistic effect of travelling near the speed of light.
When you're travelling away near the speed of light, the clock will appear to tick slower than it should have been if you were just to account for your acceleration as you did above.
Likewise, when you're returning to Earth at near lightspeed, the clock will not speed up as you expect; even clocks that are located perpendicular to your path of travel and thus shouldn't be affected by your speed as you pass them will seem to move slower.
(Yes, relativism is a bitch)
Edited to fix spelling. |
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| Edited by - Dr. Mabuse on 12/16/2008 07:57:34 |
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Boron10
Religion Moderator
USA
1266 Posts |
Posted - 12/16/2008 : 08:35:40 [Permalink]
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Originally posted by BigPapaSmurf
So as I understand it, poorly, the idea goes something like this...
Im moving away from earth at an accelerating rate and I look back at the clock on Earth, as I move faster the photons reflecting off the clock take longer to reach me, thus giving the impression that time is slowing down for me. As I approach the speed of light the clock comes alomst to a halt...
Now the popular version of this goes that when I get back to Earth my twin will be older than I, but if I turned around and returned to earth at any speed wouldnt the clock appear to move faster until I reached earth? The photons received by my eyes from the clock should increase should they not if I am moving towards them?
I seem to remember Einstein saying this was a pointless thought experiment and it was taken too literally by the media. |
The fundamental point that you are trying to make is that light seems faster or slower depending on your direction of travel. According to Einstein the speed of light never changes, regardless of your frame of reference (he actually wanted to call it "The Theory of the Constancy of the Speed of Light', but "Relativity" was a better headline). In other words, photons will always leave and reach you at exactly the speed of light. No faster, no slower, regardless of your speed or direction of travel.
Hope that helps!
Then you start considering time dilation... |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 12/16/2008 : 08:48:27 [Permalink]
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| Yes I get that C doesnt change, but wouldnt you be receiving more photons per second to your eye if moving towards the source/clock? |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Boron10
Religion Moderator
USA
1266 Posts |
Posted - 12/16/2008 : 09:18:08 [Permalink]
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Originally posted by BigPapaSmurf
Yes I get that C doesnt change, but wouldnt you be receiving more photons per second to your eye if moving towards the source/clock? |
Nope. You would get some Doppler effect (the photons would arrive with a different energy and show a different color), but the number of photons per unit time shouldn't change. |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 12/16/2008 : 11:57:20 [Permalink]
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Alright, lets try a little thought experiment and you can tell me how exactly I'm not thinking clearly...
So we have a photon emitter at point A which emits one photon every second(in the same direction) We move away from Point A at 10%C in the same direction as the photons, at rest we saw one photon per second, in motion we see one every 1.1 seconds? Now we reverse direction and move towards the emitter at 10%C, would we not see one (blue shifted)photon every 0.9 seconds? |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
| Edited by - BigPapaSmurf on 12/16/2008 12:13:20 |
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H. Humbert
SFN Die Hard
USA
4574 Posts |
Posted - 12/16/2008 : 11:57:36 [Permalink]
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I never understood how you were supposed to see the clock anyway. I can barely see the clock across my room, let alone a clock on an Earth receding away at the speed of light. I guess Einstein though everyone in the future would just own really big clocks, but I think he was wrong about that.
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"A man is his own easiest dupe, for what he wishes to be true he generally believes to be true." --Demosthenes
"The first principle is that you must not fool yourself - and you are the easiest person to fool." --Richard P. Feynman
"Face facts with dignity." --found inside a fortune cookie |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 12/16/2008 : 12:12:47 [Permalink]
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I use the solar wobble with jupiter as my home clock.
Edit: It's really more of a pain than you might imagine as I require an orbital telescope and a planet sized mirror out near the Oort cloud just to see the wobble. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
| Edited by - BigPapaSmurf on 12/16/2008 12:16:49 |
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Ricky
SFN Die Hard
USA
4907 Posts |
Posted - 12/16/2008 : 17:45:39 [Permalink]
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Originally posted by Boron10
Originally posted by BigPapaSmurf
Yes I get that C doesnt change, but wouldnt you be receiving more photons per second to your eye if moving towards the source/clock? |
Nope. You would get some Doppler effect (the photons would arrive with a different energy and show a different color), but the number of photons per unit time shouldn't change.
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I don't believe this is correct. The Doppler effect is a change in color which directly relates to a change in the frequency.
However, I think this is missing the point. Yes, you receive less photons when you move away and more when you move toward something per unit time. But this is not the phenomena that relativity refers to. It's not just the appearance of time that slows, but time itself slows. It has nothing to do with you "looking at a clock", that is only a metaphor which allows humans to grasp the passage of time. The amount or rate of photons hitting your eye is not of interest.
The best thought experiment I have heard of is to build two clocks that work by having two mirrors and a photon each. The photon bounces in between the mirrors like a never ending game of Pong, and this allows us to measure time. Place one of these clocks on a space ship, and one on the Earth. Let the ship accelerate to a point that is close to the SoL.
Assume from here on that "looking" happens instantaneous, that the information arrives to the observer in 0 time.
The observer on Earth looks up at the ship, and sees the photon bouncing around. However, this photon isn't just moving back and forth between the mirrors. The photon is moving along with the ship in some (straight) direction. Therefore, if the photon in the clock on the ground was bouncing back and forth at the same rate that the photon in the clock on the ship was, then the photon on the ship would be traveling faster than the speed of light relative to the observer on the ground. This can't possibly happen, so therefore from the ground, the rate of the photon on the ship looks like its rate is smaller than the rate of the photon on the ground when viewed from on the ground.
Now consider the point of view from the ship. Relativity says that any point of view is just as equal as any others, so we can view the ship as sitting still and the Earth moving away at a speed close to the speed of light. In this case, everything still holds. The same reasoning as above allows us to conclude that from on the ship, the rate of photon on the ground is smaller than the rate of the photon on the ship.
However each photon is traveling at the speed of light, not only relative to the observer standing next to it, but also the observer standing far away. If the passage of time was the same for each person, we would get a contradiction. Under the hope that this universe can't have contradictions, we conclude that the passage of time itself must change.
Notice how this had nothing to do with the amount or frequency of the photons hitting the observer's eyes. |
Why continue? Because we must. Because we have the call. Because it is nobler to fight for rationality without winning than to give up in the face of continued defeats. Because whatever true progress humanity makes is through the rationality of the occasional individual and because any one individual we may win for the cause may do more for humanity than a hundred thousand who hug their superstitions to their breast.
- Isaac Asimov |
| Edited by - Ricky on 12/16/2008 17:58:25 |
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Boron10
Religion Moderator
USA
1266 Posts |
Posted - 12/16/2008 : 18:26:50 [Permalink]
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Originally posted by BigPapaSmurf
Alright, lets try a little thought experiment and you can tell me how exactly I'm not thinking clearly...
So we have a photon emitter at point A which emits one photon every second(in the same direction) We move away from Point A at 10%C in the same direction as the photons, at rest we saw one photon per second, in motion we see one every 1.1 seconds? Now we reverse direction and move towards the emitter at 10%C, would we not see one (blue shifted)photon every 0.9 seconds? |
Oh, I see what you're saying.
Since, in that second, you have increased (or decreased) the distance from the source of light by a distance of d = v/t = (0.1)c/t = (3x10^7 m/sec)/(1 sec) = 3x10^7 m, which means it takes each photon more (or less) time to get to you. The difference in time it takes would be t = d/c = (3x10^7 m)/(3x10^8 m/sec) = 0.1 sec, so you are exactly right.
I apologise, I had misunderstood your question before, and allowed myself to get tripped up.
What you may be talking about in the OP is a portion of the Twin Paradox. The short answer is that it takes time to change direction and during that time you are not in an intertial frame. The long answer is ... I will have to think about it, because I am not entirely sure.
Ricky has a good explanation, though it seems it hasn't really answered your question. Neither, in fact, have I. |
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Dave W.
Info Junkie
USA
26020 Posts |
Posted - 12/16/2008 : 19:49:29 [Permalink]
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Originally posted by Boron10
Oh, I see what you're saying.
Since, in that second, you have increased (or decreased) the distance from the source of light by a distance of d = v/t = (0.1)c/t = (3x10^7 m/sec)/(1 sec) = 3x10^7 m, which means it takes each photon more (or less) time to get to you. The difference in time it takes would be t = d/c = (3x10^7 m)/(3x10^8 m/sec) = 0.1 sec, so you are exactly right. |
Except that calculated that way, the photons would look like they're only going 0.9C when they meet the ship, which can't happen since they must fly at C in all inertial frames.
However, at 0.1C, the Lorenz factor isn't anywhere near 1.1 (it's 1.005; it doesn't get up to 1.1 until 0.417C or so), and I'm not well-enough versed in the math of Relativity to make up for the discrepancy. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 12/17/2008 : 05:31:03 [Permalink]
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| Thanks guys, the exact numbers are not nessesary, just needed to clear that up so I could sleep at night. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Boron10
Religion Moderator
USA
1266 Posts |
Posted - 12/18/2008 : 09:16:52 [Permalink]
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Originally posted by Dave W.
Originally posted by Boron10
Oh, I see what you're saying.
Since, in that second, you have increased (or decreased) the distance from the source of light by a distance of d = v/t = (0.1)c/t = (3x10^7 m/sec)/(1 sec) = 3x10^7 m, which means it takes each photon more (or less) time to get to you. The difference in time it takes would be t = d/c = (3x10^7 m)/(3x10^8 m/sec) = 0.1 sec, so you are exactly right. |
Except that calculated that way, the photons would look like they're only going 0.9C when they meet the ship, which can't happen since they must fly at C in all inertial frames.
However, at 0.1C, the Lorenz factor isn't anywhere near 1.1 (it's 1.005; it doesn't get up to 1.1 until 0.417C or so), and I'm not well-enough versed in the math of Relativity to make up for the discrepancy. |
No, that's what I was thinking originally; however, from the traveler's perspective, it just looks like the photons are released at different intervals, not like the photons are traveling at different speeds. |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 12/19/2008 : 04:47:18 [Permalink]
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| Actually the color shift would suggest otherwise, wouldnt it? |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Boron10
Religion Moderator
USA
1266 Posts |
Posted - 12/19/2008 : 10:31:34 [Permalink]
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Originally posted by BigPapaSmurf
Actually the color shift would suggest otherwise, wouldnt it? |
No, the color shift only means the energy (frequency) of each photon has changed, but the speed at which the photon arrives doesn't change at all.
Just like waves in the ocean. Say you have waves moving at 5 km/h. You might have three waves breaking on the shore within one minute, or maybe just one per minute. That has no effect on the speed the wave travels, just the number of oscillations per unit time.
I am still (in the back of my mind, so I am admittedly not putting too much effort into it) trying to resolve the frequency of photon arrival based on relative distance thing .... |
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Dr. Mabuse
Septic Fiend
Sweden
9687 Posts |
Posted - 12/19/2008 : 12:02:39 [Permalink]
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Originally posted by Boron10
I am still (in the back of my mind, so I am admittedly not putting too much effort into it) trying to resolve the frequency of photon arrival based on relative distance thing ....
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It should be the same formula as for calculating dopper shift in audio, except you exchange the speed of sound for the speed of light. |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
Dr. Mabuse whisper.mp3
"Equivocation is not just a job, for a creationist it's a way of life..." Dr. Mabuse
Support American Troops in Iraq:
Send them unarmed civilians for target practice..
Collateralmurder. |
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Stupid time-space
