- #1
soup_
- 13
- 0
Okay, weird question. Sorry if this is really stupid but it's been bugging at me for days now.
First, let me lay out my current assumptions/understanding of what's going on.
The current theory seems to be (to an amateur like myself) that there is no fixed space-time. That to talk about an absolute point in space or in time is meaningless. (1)
We can only talk about what we can observe from are own frame of reference. For example, I've heard that in some sense the edge of the observable Universe is something like 40 billion light years away (as the Universe has been expanding since the light left those distant points) but since the light (and therefore time) from the edge has taken 13.7 (or whatever) billion years to reach us, this is the distance we say it is from us as there is no sense of the word distance that would be appropriate to describe it as 40 billion. (2)
Therefore, there should be no difference to the Universe between our galaxy sitting still and every other galaxy moving away from us and, say, Andromeda sitting still and every other galaxy (including ours) moving away from it. Since there is no absolute frame of reference, we can't tell which it is (3) and it really doesn't matter. (4)
Ok, now into the troubling stuff.
Does this mean that if I stand in my yard and throw a ball down the street that there is no way to say for sure whether the ball is moving away from me or (especially if I have a pet cockroach sitting on the ball) if the ball is sitting still and the entire universe, or at least some big part of it surrounding the ball, is moving? (5)
If (5) is incorrect, that there is a difference, then I feel like one of my understandings above has to also be incorrect. Eg. There must be an absolute frame of reference, etc.
If (5) is correct, that there is no difference, then I am confused :)
Let's say I perform the atomic clock experiment where I have two synced up atomic clocks. I sit in my yard with one of them and I fire the other one into space. It goes around the Earth a few dozen times at a good speed and then (because I'm an awesome amateur rocket scientist in this hypothetical) it's on-board computer brings it safely back to me. I would observe that the clock I fired up has _lost_ time. That is, it will be behind the clock that's been holding my beer while I waited for the one in space to come back to me, correct? (6)
Ok, cool. Now what if instead of getting it to orbit the earth, I get it to orbit the sun? What if I launched it in mid summer, made it follow Earth's orbit at the same velocity as Earth but in the opposite direction, and had it land back in my yard in mid winter? What would the clocks read? (7)
What if I launched it in mid summer, again following Earth's orbit in the opposite direction, but this time tried to give it velocity such that it would land in my yard exactly one year later (ie. zero velocity in some sense, but obviously it is moving away from me at the rate at which the Earth traces it's orbit around the sun)? What would the clocks read? (8)
Ok, now suppose my distant cousin James, who lives on Jupiter nowadays, has been having the same issue with relativity. He knows what I've been up to and he's got an experiment of his own. He gets in his spaceship with a couple of atomic clocks and heads on over to Earth. But instead of landing on Earth and repeating my experiment he decides to give it a twist. He hangs out in the Earth's orbit around the sun, perhaps resting his beer on the clock I've just launched in (8) and sends one of his clocks to sit in my yard while he waits for the Earth to go around the Sun. After a year has passed, his clock shoots back up and he collects it with his Canadarm. I guess if he's feeling nice, he can also take his beer off my clock and let it back out into space so it can return to me and I can record my observations.
So, what would the clocks read? (9)
Let's call my clocks EY (Earth,yard) and ES (Earth,space) and my cousin's clocks JS (Jupiter,space) and JY (Jupiter,yard - being the one that sits in my yard).
Obviously, I don't care that JY and EY have never been synced and I'm only interested in EY relative to ES and JY relative to JS.
I feel like the experiments should match up. That it shouldn't matter that I'm sitting in my yard while all this is happening and he's sitting in his space ship. On the other hand if we both observe the same thing, let's say the clocks in space both lose time relative to the clocks on Earth, then James will have experienced the clock that was away from him having sped up while I would have experienced the clock that was away from me as having slowed down. Why? What's the difference? It feels like we've both performed the same experiment so shouldn't we observe the same results? (10)
If you disagree that we have performed the same experiment, then let me throw one more hypothetical. James and I meet up in space. Me in my space ship, him in his. Together we go past the edge of the Milky Way, out into no man's land. It's a long trip but we've discovered the secret to immortality, so we're fine. Once we get out a good distance from any galaxies, we sync up all four clocks. We exchange one set of clocks (or not, whatever) and we both engage our thrusters full throttle away from each other for a year. After a year is up (let's say we count in our heads, 1-one thousand, 2-one thousand and we are perfect counters) we reverse direction and meet back up in the middle. What do the clocks read? (11)
I guess that brings me to the "how much stuff is in the frame" part of my question. If clock ES slows down relative to clock EY in (6), (7), or (8), then why? Why not the other way around? The only reason I can fathom is that I have the Earth with me and this changes things somehow, but that doesn't make any sense... does it? (12)
Thanks for your patience,
soup
First, let me lay out my current assumptions/understanding of what's going on.
The current theory seems to be (to an amateur like myself) that there is no fixed space-time. That to talk about an absolute point in space or in time is meaningless. (1)
We can only talk about what we can observe from are own frame of reference. For example, I've heard that in some sense the edge of the observable Universe is something like 40 billion light years away (as the Universe has been expanding since the light left those distant points) but since the light (and therefore time) from the edge has taken 13.7 (or whatever) billion years to reach us, this is the distance we say it is from us as there is no sense of the word distance that would be appropriate to describe it as 40 billion. (2)
Therefore, there should be no difference to the Universe between our galaxy sitting still and every other galaxy moving away from us and, say, Andromeda sitting still and every other galaxy (including ours) moving away from it. Since there is no absolute frame of reference, we can't tell which it is (3) and it really doesn't matter. (4)
Ok, now into the troubling stuff.
Does this mean that if I stand in my yard and throw a ball down the street that there is no way to say for sure whether the ball is moving away from me or (especially if I have a pet cockroach sitting on the ball) if the ball is sitting still and the entire universe, or at least some big part of it surrounding the ball, is moving? (5)
If (5) is incorrect, that there is a difference, then I feel like one of my understandings above has to also be incorrect. Eg. There must be an absolute frame of reference, etc.
If (5) is correct, that there is no difference, then I am confused :)
Let's say I perform the atomic clock experiment where I have two synced up atomic clocks. I sit in my yard with one of them and I fire the other one into space. It goes around the Earth a few dozen times at a good speed and then (because I'm an awesome amateur rocket scientist in this hypothetical) it's on-board computer brings it safely back to me. I would observe that the clock I fired up has _lost_ time. That is, it will be behind the clock that's been holding my beer while I waited for the one in space to come back to me, correct? (6)
Ok, cool. Now what if instead of getting it to orbit the earth, I get it to orbit the sun? What if I launched it in mid summer, made it follow Earth's orbit at the same velocity as Earth but in the opposite direction, and had it land back in my yard in mid winter? What would the clocks read? (7)
What if I launched it in mid summer, again following Earth's orbit in the opposite direction, but this time tried to give it velocity such that it would land in my yard exactly one year later (ie. zero velocity in some sense, but obviously it is moving away from me at the rate at which the Earth traces it's orbit around the sun)? What would the clocks read? (8)
Ok, now suppose my distant cousin James, who lives on Jupiter nowadays, has been having the same issue with relativity. He knows what I've been up to and he's got an experiment of his own. He gets in his spaceship with a couple of atomic clocks and heads on over to Earth. But instead of landing on Earth and repeating my experiment he decides to give it a twist. He hangs out in the Earth's orbit around the sun, perhaps resting his beer on the clock I've just launched in (8) and sends one of his clocks to sit in my yard while he waits for the Earth to go around the Sun. After a year has passed, his clock shoots back up and he collects it with his Canadarm. I guess if he's feeling nice, he can also take his beer off my clock and let it back out into space so it can return to me and I can record my observations.
So, what would the clocks read? (9)
Let's call my clocks EY (Earth,yard) and ES (Earth,space) and my cousin's clocks JS (Jupiter,space) and JY (Jupiter,yard - being the one that sits in my yard).
Obviously, I don't care that JY and EY have never been synced and I'm only interested in EY relative to ES and JY relative to JS.
I feel like the experiments should match up. That it shouldn't matter that I'm sitting in my yard while all this is happening and he's sitting in his space ship. On the other hand if we both observe the same thing, let's say the clocks in space both lose time relative to the clocks on Earth, then James will have experienced the clock that was away from him having sped up while I would have experienced the clock that was away from me as having slowed down. Why? What's the difference? It feels like we've both performed the same experiment so shouldn't we observe the same results? (10)
If you disagree that we have performed the same experiment, then let me throw one more hypothetical. James and I meet up in space. Me in my space ship, him in his. Together we go past the edge of the Milky Way, out into no man's land. It's a long trip but we've discovered the secret to immortality, so we're fine. Once we get out a good distance from any galaxies, we sync up all four clocks. We exchange one set of clocks (or not, whatever) and we both engage our thrusters full throttle away from each other for a year. After a year is up (let's say we count in our heads, 1-one thousand, 2-one thousand and we are perfect counters) we reverse direction and meet back up in the middle. What do the clocks read? (11)
I guess that brings me to the "how much stuff is in the frame" part of my question. If clock ES slows down relative to clock EY in (6), (7), or (8), then why? Why not the other way around? The only reason I can fathom is that I have the Earth with me and this changes things somehow, but that doesn't make any sense... does it? (12)
Thanks for your patience,
soup