Question about time and measurement

  • #51
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A------------------------------B

Let's say that you have two identical atomic clocks with identical readings at point A. Now clock 1 is moved fast from A to B, and clock 2 is moved slowly from A to B. Then you compare the two clocks at B and you will find that clock 1 is behind on clock 2. In other words, the clock that moved slower will have recorded more units of time than the clock that moved fast.
I'm wondering if this is indeed correct. As you have described the thought experiment, clock 1 moves quickly from point A to point B, but it then it has to stop and wait for clock 2 to catch up, so that we can compare them. So for a period of time clock 1 is the faster moving clock, but then it stops and clock 2 becomes the faster moving clock. Do these two effects cancel each other out such that the two clocks will actually read the same time when clocks 1 and 2 reach point B? Or is the effect of increased time dilation exponentially greater as speed increases such that the faster moving clock will have actually experienced less time when both clocks ultimately reach point B?
 
  • #52
Yes Fiziqs.
To make it simpler I try to make these two objects in the thought experiment traveling in circles so that they just meet up on there own orbit every few orbits or something.
If the fast object has to stop (and i am trying to figure out why when we "stop" we dont just age ininiftely by the pattern of time dilation) wait for the slow object I would assume that when they met they would actually have experienced the exact same amount of time.

Just like with the astronaut returning to earth to see everyone age dramatically, the Earth doesn't speed up to catch the astronaut, and the astronaut doesn't slow down and wait for the earth. He, in most cases, will turn around and head back to earth.

Drakkith that is a good graph.

But I still do not understand why we can STOP the accumulation of time, but we can only speed up the accumulation of time by slightly over one second per earth second.

And you keep saying to me there is no point in trying to understand what it would be like to travel at light speed, because we have no idea.

Yet we have made the assumption that time stops?... right. So if it clearly shows time stopping at the speed of light you must agree.

It is pretty easy to understand time stopping.
You will experience one second per second, but the next second will never come, and you will never take the time to have this thought, and your spaceship would never take the time to fire out rocket fuel or ions or whatever.
Best way to really grasp it is that you are dead for a moment because you are frozen in time.

And I would much rather talk about why time cannot speed up according to you.And other physicists. (im assuming your a physicist?)

If you were to reach 0 speed, then why would you only experience 1.000004 seconds per earth second.
you are barely aging any faster at all, but we are assuming you are not moving?

I should mention that if you were in a 0 rest frame, you would just experience one second per second, while anything at the speed of light would perceive you to age to infinity.
Maybe this is where I am getting confused.
Maybe I am correct, but we are already going so slow that our accumulation of time is almost at its maximum speed.
Things moving fast already see us aging at an incredible rate.

But this being said I know that our planet is traveling very fast around a star that is traveling very fast around a galaxy that is traveling very fast (maybe).
We could probably go a bit higher than 1.0000004 seconds per earth second by going slower.
 
  • #53
HHHMMMMM u know what.
at the speed of light you would perceive any slower speed to age to infinity.
Maybe this is where I have not understood this?

an object at rest is already aging to infinity.
but we are barely moving so relative to us, it seems to be just ticking slightly faster.
we are already accumulating time at almost the maximum rate.


But still, to add to this, could we not judge how fast an object has moved over its journey compared to us by how much more or less time it accumulated?

Einstein says when two objects are in motion relative to each other they have no idea if one they are still and the other object is moving toward them....

Our spaceships could flash a little signal to the other spaceship to start a clock,

and the one that was moving would be like " dude, i barely felt any time at all, you must have been waiting for soo long"

So cant we gauge how fast an object is moving, by how much time it accumulates, in comparison to another object?
 
  • #54
I think I answered my own question maybe.
We are already ALMOST experiencing the fastest rate of time we can accumulate.
 
  • #55
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I'm wondering if this is indeed correct. As you have described the thought experiment, clock 1 moves quickly from point A to point B, but it then it has to stop and wait for clock 2 to catch up, so that we can compare them. So for a period of time clock 1 is the faster moving clock, but then it stops and clock 2 becomes the faster moving clock. Do these two effects cancel each other out such that the two clocks will actually read the same time when clocks 1 and 2 reach point B? Or is the effect of increased time dilation exponentially greater as speed increases such that the faster moving clock will have actually experienced less time when both clocks ultimately reach point B?
If the clocks travel at the same speed then the two clocks will be equally retarded, so that they are in synch wiht each other. Instead, we compared a clock that was transported rapidly from A to B with a clock that was transported much more slowly from A to B. See §4 of http://fourmilab.ch/etexts/einstein/specrel/www/
 
  • #56
Harrylin, that is what Fiziqs was saying though.
We cant go from A to B and have this effect work. Ill explain what I mean.
If both clocks have to travel the same distance, this means they experienced the same time rate if they have to meet up.
The fast clock must go much farther and return to the other object for this to work. So the fast clock does a continuous loop and checks back in once in a while. Or the fast clock zooms away from the earth turns around and zooms back. The fast clock could even zoom past the earth and turn around and just do a back and forth guitar string pattern over the earth. something.

If we are sending two clocks from A to B, one going slow, one going fast, we would need Buddah to be the 3rd observer and count a certain amount of time, maybe after the fast clock is halfway through the journey or something, and check both the clocks at the same time and see which one has accumulated more or less time.

Its much better to comprehend if the fast clock makes the effort to get back to the slow clock for the comparison.

once the fast clock reaches point B, to compare clocks he would have to wait. and all of the extra anti aging he would have would be completely cancelled out while driving miss Daisy meanders through the journey
 
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  • #57
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We cant go from A to B and have this effect work. Ill explain what I mean.
If both clocks have to travel the same distance, this means they experienced the same time rate if they have to meet up.
Actually questionator89 I think harrylin is correct, even if clock 1 has to stop and wait for clock 2 their clocks will not read the same. The reason that I think this is true is that the time dilation effect is not linear. In other words both clocks would end up reading the same time if going twice as fast simply meant experiencing half the passage of time. But time dilation isn't linear, going twice as fast will cut the passage of time by more than half.

Thus if clock 1 travels at just under the speed of light it will experience very little time at all, and if clock 2 is traveling at exactly half the speed of clock 1 it will nonetheless experience much more than twice the time. Going faster for a shorter period of time will have more of an effect than traveling slower for a longer period of time.

At least that's how it appears to me.
 
  • #58
Right. But isn't it all related to what distance you went through space time to give you this dilation?

At the end of the road with object one they measure the time. But then it takes the other object much longer to reach the end of the road. But once it reaches it they measure this time.
Under this scenario I can understand a discrepancy.

But if they measure both clocks at the same time, they would have to wait while the other object finishes the journey and the faster object sits not moving, which means the object which reached it faster is now experiencing the maximum accumulation of time that any object can experience because it is at rest. the slow moving clock is still moving towards it and experiencing slightly less time accumulation.
It is not linear it is an exponential increase, but it continues both ways.
To sit and wait for the other clock to arrive would take just as long as the entire journey that the slower clock perceived.
 
  • #59
Harrylin,
Could you explain one section in that link that you shared?
The part where the light particle is bouncing off a reflector and they are determining the difference in force between the light that hit the surface and left, and determining what force was enacted upon the surface (or "work done")?
I cant follow the math here. are they saying that the reflector feels the photons bounce off and moves?

I have heard of the solar sails that we are considering using for spacecraft, and ionic propulsion, but I do not understand how this works.

If a photon was massless how can it apply any force?
I thought that light bent with gravity only because gravity is warping the straight line that light would have normally travelled. What is the weight of an electron?
 
  • #60
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Harrylin,
Could you explain one section in that link that you shared?
The part where the light particle is bouncing off a reflector and they are determining the difference in force between the light that hit the surface and left, and determining what force was enacted upon the surface (or "work done")?
I cant follow the math here. are they saying that the reflector feels the photons bounce off and moves?
[..]
If a photon was massless how can it apply any force?
I thought that light bent with gravity only because gravity is warping the straight line that light would have normally travelled. What is the weight of an electron?
That's a completely different topic; anyway in §8 he uses the concept of light waves and not photons - no light particles. Light pressure is already known from classical optics, compare https://en.wikipedia.org/wiki/Radiation_pressure.
Light energy is the square of its amplitude. By definition the work done on an object equals the energy that entered it minus the energy that was given back. if you want to discuss it further, please start it with a new thread.
 
  • #61
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I'm wondering if this is indeed correct. As you have described the thought experiment, clock 1 moves quickly from point A to point B, but it then it has to stop and wait for clock 2 to catch up, so that we can compare them. So for a period of time clock 1 is the faster moving clock, but then it stops and clock 2 becomes the faster moving clock. Do these two effects cancel each other out such that the two clocks will actually read the same time when clocks 1 and 2 reach point B? Or is the effect of increased time dilation exponentially greater as speed increases such that the faster moving clock will have actually experienced less time when both clocks ultimately reach point B?
You could have an observer at B record each reading when they arrive, or stop each clock when it arrives. The results will be the same.
 
  • #62
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Harrylin, that is what Fiziqs was saying though.
We cant go from A to B and have this effect work. [..]
Sorry I can't follow you. As I said in my post #5, you seemed to correctly understand it in your post #1. But now you seem to say that what you said cannot be right, so that after all the explanations you now misunderstand it for a reason that I cannot follow. You seem to reason against yourself - and I give up!
 
  • #63
Yeah your right Phyti but that is irrelevant. Stopping the clock as it arrives, or writing down the exact time that it arrives is still recording the stopped time of the arrival. they are literally exactly the same.
the point is if you were to record both clocks at the same time (unless you did this before the first one reached its destination) there would be no time accumulation discrepancy.they would have aged the same.
If the other clock had to sit at rest and waiting for the other clock to arrive, then you recorded both clocks once the slow one arrived, they would read the same time.

Whereas if you as a 3rd observer were to record both clocks in motion before they arrived, the slow clock will have recorded many more units of time, and the fast clock would have recorded fewer.

Lets say your momentum was faster so your time is slower than both.
The journey starts , you wait 10 seconds then record how many seconds both of the other clocks experienced along the way. The fast clock will have experienced 13 seconds, but the slower clock would have experienced 35 seconds and is still farther behind than the faster clock.
 
  • #64
Sorry I can't follow you. As I said in my post #5, you seemed to correctly understand it in your post #1. But now you seem to say that what you said cannot be right, so that after all the explanations you now misunderstand it for a reason that I cannot follow. You seem to reason against yourself - and I give up!
I didnt understand something crucial before actually, that I do understand now. I already understood the entire concept except one thing. I falsely thought that if we were to stop something in orbit, if it were truly at rest, it would experience an infinite amount of aging.
what I forgot to piece together is that the only thing that could ever experience another object to age infinitely is something going the exact speed of light.
because we on earth are moving, but not moving very fast, when we drop something into orbit it only experiences slightly more units of time than we do.
because we are already experiencing close the maximum rate of time passage due to how far away from the speed of light we are.

Harrylin youve been awesome I totally understand your frustration
 
  • #65
Anyways my original question was answered if anyone hasn't understood that.
Thanks everyone, secrest out.


I am starting two new unrelated threads

-Can we determine what direction our star is traveling and at what velocity, based on time dilation
-Radiation Pressure and the weight of electromagnetic momentum
 
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  • #66
Drakkith
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But I still do not understand why we can STOP the accumulation of time, but we can only speed up the accumulation of time by slightly over one second per earth second.
What are you talking about? First, we can't stop the accumulation of time. Nothing you could do to an object will ever make it freeze in time.

Also, speed your spaceship up to 99.99999% c. The Earth is now experiencing severe time dilation and your clock will be accumulating MORE time than the Earth is.

Yet we have made the assumption that time stops?... right. So if it clearly shows time stopping at the speed of light you must agree.
Who made this assumption? Not me. Not science. I've already explained that we can't accelerate an observer to c so we can't predict what would happen if we could.

It is pretty easy to understand time stopping.
You will experience one second per second, but the next second will never come, and you will never take the time to have this thought, and your spaceship would never take the time to fire out rocket fuel or ions or whatever.
Best way to really grasp it is that you are dead for a moment because you are frozen in time.
This is wrong. This will NEVER happen. You do not experience time dilation in your own frame.

And I would much rather talk about why time cannot speed up according to you.And other physicists. (im assuming your a physicist?)
No, I'm just a guy who reads a lot and has spent 3 years on PF learning from people who are physicists.

If you were to reach 0 speed, then why would you only experience 1.000004 seconds per earth second.
you are barely aging any faster at all, but we are assuming you are not moving?
Where are you getting these numbers from? They aren't correct. Just looking at SR, two observers at rest with respect to each other will measure the other's clock as ticking at exactly 1 second per second.

I should mention that if you were in a 0 rest frame, you would just experience one second per second, while anything at the speed of light would perceive you to age to infinity.
Maybe this is where I am getting confused.
Maybe I am correct, but we are already going so slow that our accumulation of time is almost at its maximum speed.
Things moving fast already see us aging at an incredible rate.
Again, wrong. Things moving near light speed perceive us as moving at light speed instead. To them WE are time dilated.

But this being said I know that our planet is traveling very fast around a star that is traveling very fast around a galaxy that is traveling very fast (maybe).
We could probably go a bit higher than 1.0000004 seconds per earth second by going slower.
WITH RESPECT TO WHAT FRAME OF REFERENCE????
Seriously, you need to forget everything you think you know and focus on this one particular detail until it gets hammered in. Every time you post and say something is traveling fast I want you to add in "with respect to X frame", where X is whatever object or observer.

HHHMMMMM u know what.
at the speed of light you would perceive any slower speed to age to infinity.
Maybe this is where I have not understood this?
You are not understanding it, because you keep trying to figure out what happens to an observer at c. Stop it. It's only confusing you.

Einstein says when two objects are in motion relative to each other they have no idea if one they are still and the other object is moving toward them....

Our spaceships could flash a little signal to the other spaceship to start a clock,

and the one that was moving would be like " dude, i barely felt any time at all, you must have been waiting for soo long"

So cant we gauge how fast an object is moving, by how much time it accumulates, in comparison to another object?
Of course we can. But guess what? However fast that object is moving, to it YOU are moving at the same velocity instead.
 
  • #67
Wow drakkith you dont even get it, you are just nit picking bad grammar.
In every scenario there is a reference so I dont see where you get lost.
There is nothing we can do to freeze time? Except go the speed of light or apparently get sucked into a black hole.

Maybe you don't get it.

Besides the question I was asking was why cant we slow something down enough to age infinitely

Now I know the answer. The only thing that would perceive any object to age infinitely is something going the speed of light, where time freezes.
Ill clarify so you dont nit pick it to death, when i say "perceive" i dont mean someone going at the speed of light has the time to think about anything because time never begins and time never ends for an object traveling this speed.

In any case, when we drop something into orbit around the earth it experiences only slightly more time accumulation compared to earth because earth is already going almost a resting rate

we are already experiencing close to the fastest rate of time accumulation we can, but still perceive 1 second per second.

so the question is ANSWERED.
And as far as in respect to what when you keep asking what reference or whatever.
When I say "going fast" i mean in respect to the total light speed, or in respect to normal earth speed.
 
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  • #68
Drakkith
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Wow drakkith you dont even get it, you are just nit picking bad grammar.
In every scenario there is a reference so I dont see where you get lost.
No, you don't appear to understand reference frames and why they are important to SR, otherwise you wouldn't be asking about the movement of the galaxy and trying to slow things down.

In any case, when we drop something into orbit around the earth it experiences only slightly more time accumulation compared to earth because earth is already going almost a resting rate
What frame are you comparing Earth's motion against? The Sun? If so, then Earth and the satellite have identical amounts of time dilation over a period of time at least as long as the orbital period of the satellite around the Earth.

so the question is ANSWERED.
And as far as in respect to what when you keep asking what reference or whatever.
When I say "going fast" i mean in respect to the total light speed, or in respect to normal earth speed.
Normal Earth speed in respect to what frame? The Sun? The galaxy? And no, you can't reference "total light speed" because light travels at c in all inertial frames of reference. We cannot assign an inertial frame of reference to light.

Edit: See this thread - https://www.physicsforums.com/showthread.php?t=714274
 
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  • #69
Drakkith,
I am comparing earths motion against a clock which is at rest, not orbiting. Just like what I have been talking about for the past 60 posts and over 2 threads.
Each time I post I am pretty sure I mention this single scenario.

Drop a clock into space at rest, do a one year orbit around the sun, find how much more time accumulated for the resting clock compared to the clock on earth which was moving.

The difference in time dilation should also give us a difference in velocity if the velocity is unknown, because we know how much time is dilated by how fast an object is moving.

So another scenario,
An astronaut leaves earth at an incredible rate for a period of time then stops.
You say the earth could view it as speeding away from the astronaut, but the astronaut will view it as he is speeding away from earth. They cannot tell who moved away from who.
But if the astronaut were to speed back to earth and compare a difference between time dilation, he would have experienced much less time in comparison to earth. Is this wrong?

So if two objects wanted to tell which object was actually moving they could just compare how much time accumulated for each of them since the astronaut left the earth, or the earth left the astronaut. no?
 
  • #70
im pretty sure that light doesn't always appear to be going "the speed of light"
I have said this before too, light is constant. You are saying this as well, but I think you think this means no matter what speed you are going a laser will always shoot out at the speed of light. But when in reality if you have any momentum at all, light will go slower
This means no matter what speed you are going, light will always go the same speed, separate from your speed.
this means if you are going fast light will appear to be going slower, and if you are going slow light will appear to be going faster.

If you were traveling at 50% of the total speed of light, for light to optically appear normal to you, it would have to be going 150% the speed of light which is impossible.

And in fact there is an inertial frame of reference for light. Because light has momentum it also displays properties of inertia and mass. This is how solar sails work.
When radiation hits an object the object feels this object as if it had some mass to it because of radiation pressure or something.
 
  • #71
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So if two objects wanted to tell which object was actually moving they could just compare how much time accumulated for each of them since the astronaut left the earth, or the earth left the astronaut. no?
No, because they could both be moving. There is no such thing as actually moving. There is only moving wrt some frame.
 
  • #72
So then how does time dilation appear in reality at all if what you say is true.
This means that if I were to travel around at very close to the speed of light, and come back to earth, no discrepancy between minutes felt will be notable because the earth also could have been the object speeding around at close to the speed of light?

So time dilation does not actually appear in reality?

The big difference being between the object which actually moved is that it accelerated, traveled fast for a while, then returned to the same velocity for clock comparison.
So firstly the earth would not have felt any acceleration, and would not have experienced any time dilation by accelerating.

If time dilation does not effect reality then why is it being discussed at all
 
  • #73
Drakkith
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Drakkith,
I am comparing earths motion against a clock which is at rest, not orbiting. Just like what I have been talking about for the past 60 posts and over 2 threads.
Each time I post I am pretty sure I mention this single scenario.
Which would be fine if we were talking about the exact same resting frame the whole time, but we are not. You cannot just say the clock is at rest when we have different conditions for different observers. You must specify what frame of reference you are using or things will not make sense and the conversation will be very confusing. As this thread has shown.

Drop a clock into space at rest, do a one year orbit around the sun, find how much more time accumulated for the resting clock compared to the clock on earth which was moving.
I assume the clock in space is kept at rest with respect to the Sun's frame?

So another scenario,
An astronaut leaves earth at an incredible rate for a period of time then stops.
You say the earth could view it as speeding away from the astronaut, but the astronaut will view it as he is speeding away from earth. They cannot tell who moved away from who.
But if the astronaut were to speed back to earth and compare a difference between time dilation, he would have experienced much less time in comparison to earth. Is this wrong?
It's not wrong, it's just missing the key point in that the astronaut was accelerated while the Earth was not. Both still moved away from each other, but only the astronaut was accelerated. So while he's accelerating he can observe the Earth, do the calculations, and say, "Hey, I'M the one causing us to get further apart." Thus, when the two meet back up, the astronaut is the one who has experienced less time because he accelerated to a frame of reference that was no longer at rest compared to us and then returned back to the Earth's frame.

So if two objects wanted to tell which object was actually moving they could just compare how much time accumulated for each of them since the astronaut left the earth, or the earth left the astronaut. no?
Kind of. Both objects are "actually moving" with respect to each other. But the difference lies in the fact that only one was accelerated. Plus, since this motion isn't steady, you cannot know exactly what the accelerated observer did just by comparing clocks when they return. You could only get an average velocity.
 
  • #74
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The word "move" means "change position over time". Mathematically, that is dx/dt, which is velocity. So "move" means velocity (specifically nonzero velocity). Motion (velocity) is relative, but acceleration is not. So while it is incorrect to say that one object "actually moved" it is not incorrect to say that one object "actually accelerated". The object that actually accelerated will accumulate less time.
 
  • #75
OOOOH .. Kay i get exactly where this translation was lost.
So if we were to all of the sudden become conscious and another object were all of the sudden to become conscious, they would have no idea which one was moving right?
But what I cant grasp is, one of these objects was accelerated to begin with and would be experiencing slower time, while the other one experienced faster time.
If when they became conscious they threw a signal to the other guy to start some ticker that accumulated ticks ( and both tickers were built so if they were at the same momentum they would experience the same rate of ticks) would the one that was actually moving have his ticker tick less? Right as they pass each other they flash the number of ticks each object experienced.

So one object would say your object is ticking fast and mine is ticking normally, while the other object thinks my ticker is ticking normally and yours is ticking slow?

Could we not, without knowing who was accelerated toward who, compare time dilation to find who accelerated?
or at least how much faster one is moving in the case that they are both not at rest.

Drakkith you are right we could only get an averaged velocity. But could we not use this to find out how fast our sun is moving (on average) around our galaxy?
And to answer your q from post 73 the clock is at rest, and the sun is at rest, and the earth orbits the sun for one year and picks the clock up in what the earth and the sun perceive to be the same location the clock was originally placed in.
 

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