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peteshimmon
2007-Feb-14, 06:44 PM
Am I right in stating that if two clocks are
synchronised in an inertial frame then that
synchronisation is lost if the frame is
accelerated along an axis through the
two clocks? They are separated by some
distance in the frame.

Ken G
2007-Feb-14, 07:26 PM
Yes, that is correct-- after the acceleration is over, they will be desynchronous in that original frame. Note the acceleration ends at the same clock reading on both clocks here, so the original frame will see the leading clock cease to accelerate prior to the following clock. That will explain the resulting length contraction between the clocks, seen in the original frame.

(edited: the desynchronization happens in the original frame, which stays inertial.)

peteshimmon
2007-Feb-14, 07:37 PM
Thanks Ken! Not well known is it. The clocks
can be corrected by accelerating the frame the
opposite way I expect. Or if the discrepancy is
just a smiggen one can sit nearer one of them.

Ken G
2007-Feb-14, 07:43 PM
You are right this is not well known, and that is the reason that so many people don't understand the twin paradox. Note that where you sit won't help-- that's all corrected for when you go to calculate the synchronicity (using the standard definition by Einstein).

peteshimmon
2007-Feb-14, 07:49 PM
Well if they are synchronised by a light signal
device half way between then they only read
the same from that position. Only a nit pick
surely.

dhd40
2007-Feb-14, 08:07 PM
Am I right in stating that if two clocks are
synchronised in an inertial frame then that
synchronisation is lost if the frame is
accelerated along an axis through the
two clocks? They are separated by some
distance in the frame.

Although I´ve read Ken´s answers I don´t understand how a FRAME can be accelerated. One of the clocks can be accelerated, of course, and, by this, will leave the other clock´s inertial frame. But maybe I misunderstand your question as well as Ken´s answers.
( I´ll be on vacation for a while. So please don´t expect any comments from me until the end of this months)

Ken G
2007-Feb-14, 09:50 PM
Well if they are synchronised by a light signal
device half way between then they only read
the same from that position. Only a nit pick
surely.Two clocks that are in the same inertial frame and are synchronized will be determined to be synchronized by every observer in that same frame, no matter where that observer is located, assuming that all observers are using Einstein's synchronization convention. Note they will not "see" the clocks as reading the same thing, but that's a different issue altogether.

Sam5
2007-Feb-14, 09:53 PM
Although I´ve read Ken´s answers I don´t understand how a FRAME can be accelerated.

In Einstein's original paper he used the term "system" rather than "frame".

A "system" can be a single clock. It can be a railroad car or whole train. It can be a rocket. It can be a planet. Etc.

A "system" can contain more than one clock, and when a system is accelerated, all the clocks in that system are accelerated at the same time, in the same way, and the same amount.

Ken G
2007-Feb-14, 10:06 PM
Although I&#180;ve read Ken&#180;s answers I don&#180;t understand how a FRAME can be accelerated. One of the clocks can be accelerated, of course, and, by this, will leave the other clock&#180;s inertial frame. It's my fault, I forgot to specify that the clocks become desynchronous in the original inertial frame. You are right that in their own frame, if the clocks do the same things, then they stay synchronized-- they are just one frame, together, as Sam5 also said. (And this is all special relativity-- let's not worry about what real gravity would do to all this!)

peteshimmon
2007-Feb-15, 10:49 AM
Sheesh! I did not set out to lay banana skins around. I always thought of a frame like a wire frame cube representing a volume that contains your clock or clocks. So when accelerated things in the volume show the relevant effects relative to any external observer. Now a frame can be a railway carriage or rocket ship having some sensible length. And two clocks set at each end having been synchronised either together or by a middle placed light signal will it seems be desynchronised by any acceleration along the axis separating them. Surely a bit of acceleration does not make this General Relativity and more complicated? For many people synchronisation means reading the same!

Ken G
2007-Feb-15, 01:07 PM
And two clocks set at each end having been synchronised either together or by a middle placed light signal will it seems be desynchronised by any acceleration along the axis separating them.Yes, but you have to say a little more-- they seem desynchronized to people left in the original frame. If the accelerations are the same in the frame of the clocks, then observers who are also in the clocks' frame will not see the clocks as desynchronized. Synchronization is itself a frame-dependent concept, indeed that's the reason that acceleration can cause desynchronization, so you have to identify the frame you mean. The banana peels are unavoidable.

Surely a bit of acceleration does not make this General Relativity and more complicated? For many people synchronisation means reading the same!It isn't general relativity, true, but "reading the same" is still pretty ambiguous. You cannot mean "read the same" in terms of what you'd see if you looked at their dials, that's not what synchronized means. If it were, it would not be reciprocal-- person A could think their own clock was synchronized with person B's, but person B would not think they were synchronized with A's. Einstein's convention achieves reciprocality of synchronization, which is presumably the reason that convention was chosen.

RussT
2007-Feb-16, 01:42 AM
Einstein's convention achieves reciprocality of synchronization, which is presumably the reason that convention was chosen.

And this is one of things that grav is trying to get to the bottom of in his ATM thread. However, he is mainly looking for the descepancy in the MMX, and it cannot be found there!

Part of the problem, and not the only one, is simulaneity(sp). Nothing in the macro world can be simulaneous when measuring clocks at ANY distance. The wall across the room where you are sitting is IN YOUR PAST.

Ken G
2007-Feb-16, 04:23 AM
The wall across the room where you are sitting is IN YOUR PAST.

Not necessarily. Can you not affect that wall? And must not everything you can affect be in your future?

Kaptain K
2007-Feb-16, 06:03 AM
Not necessarily. Can you not affect that wall? And must not everything you can affect be in your future?
Now you''re picking nits. If the wall I see is 6 meters away, I see it as it was about 20 nano-seconds ago. Of course, I can affect the future of the wall, but nothing I do "now" will affect the wall as I see it "now". That wall is in my past. I can only affect the wall's future.

RussT
2007-Feb-16, 07:33 AM
Not necessarily. Can you not affect that wall? And must not everything you can affect be in your future?

Yes of course you can Affect that wall, BUT to do so you or whatever you are going to "Affect" it with must move to the walls "Now"/Present.

closetgeek
2007-Feb-16, 02:17 PM
I don't remember if it was in Relativity or one of Hawking's books, but was there not a separate experiment where they send one clock flying East and one clock flying west. They were syncronized before they took off but the clock flying west was a few nano seconds ahead of the clock flying East? You are free to tell me to go back and read the books again, but I am attempting laziness first.

grant hutchison
2007-Feb-16, 03:07 PM
I don't remember if it was in Relativity or one of Hawking's books, but was there not a separate experiment where they send one clock flying East and one clock flying west. They were syncronized before they took off but the clock flying west was a few nano seconds ahead of the clock flying East? You are free to tell me to go back and read the books again, but I am attempting laziness first.I believe you're thinking of flying clocks around the world in opposite directions, and finding a time difference when they are reunited. One (the one travelling with the Earth's rotation) has travelled at a higher speed than the other.

Grant Hutchison

2007-Feb-16, 03:14 PM
I don't see what all the fuss is over synchronizing clocks. If light travels at the speed of 186,000 miles per second, that means during the interval of 1 second, it traveled 186,000 miles.

If I make a splash in a pool, is the wave the past? No, it is what it is, a wave. The wave travels a distance in a specific interval of time.

In order for there to be a present, there must be a specific instant in time, which is impossible. There is no "instant in time". In order to have a instant in time, there must be a static mass. There is no such animal as a "static mass" in this universe.

Since there is no present, there can not be a past or a future. Time is imagined by an observer. Mass is what it is, regardless of it's motion. Mass doesn't have a past, present, or future. That is all an illusion!

Ken G
2007-Feb-16, 03:30 PM
Now you''re picking nits. If the wall I see is 6 meters away, I see it as it was about 20 nano-seconds ago.

My objection was to the statement "the wall is in my past". Had he said "the wall I see is in my past", the statement would have been correct, but obvious. For is it not obvious that everthing we see is in the past? Does it not take time to analyze an image? The present is only an instant, and we never see the future, so of course all of our perceptions are of the past. That isn't relativity.

gGriffeth
2007-Feb-16, 03:31 PM
This is to the two posts above Motor Daddy:
I haven't yet learned about this, so correct me if I'm wrong, but were these battery operated clocks? In that case, wouldn't they be the same, even if someone went into the future, because the clock doesn't change with time, it changes with what its programmed to do. --
I'll try another way of explaining this if you didn't get it the first time:
The clocks were made to correspond with the measurements of time. If time was changed (speeding up) then the clocks would just keep doing what they were programmed to do, not speed up time. It's like those little birds that dive into the water then up then down.....that's constant, so if i wanted, I could use that as a measurement for time, but if i were to go on a plane and travel with the earths rotation, that bird wouldn't dive faster
Do you get what I'm trying to say? Correct me if I'm wrong.

Ken G
2007-Feb-16, 03:33 PM
Yes of course you can Affect that wall, BUT to do so you or whatever you are going to "Affect" it with must move to the walls "Now"/Present.
You said nothing can be simultaneous, but I think you meant it can't be simultaneous with our perception of it. Causality is delayed by separation, that is indeed an important truth.

gGriffeth
2007-Feb-16, 04:14 PM
can someone answer my question 2 posts up

2007-Feb-16, 05:25 PM
My objection was to the statement "the wall is in my past". Had he said "the wall I see is in my past", the statement would have been correct, but obvious. For is it not obvious that everthing we see is in the past? Does it not take time to analyze an image? The present is only an instant, and we never see the future, so of course all of our perceptions are of the past. That isn't relativity.

Describe to me an instant?

Squashed
2007-Feb-16, 05:32 PM
This is to the two posts above Motor Daddy:
I haven't yet learned about this, so correct me if I'm wrong, but were these battery operated clocks? In that case, wouldn't they be the same, even if someone went into the future, because the clock doesn't change with time, it changes with what its programmed to do. --
I'll try another way of explaining this if you didn't get it the first time:
The clocks were made to correspond with the measurements of time. If time was changed (speeding up) then the clocks would just keep doing what they were programmed to do, not speed up time. It's like those little birds that dive into the water then up then down.....that's constant, so if i wanted, I could use that as a measurement for time, but if i were to go on a plane and travel with the earths rotation, that bird wouldn't dive faster
Do you get what I'm trying to say? Correct me if I'm wrong.

If two observers, each with their own clocks, time the diving of the birds then the two calculated speeds of the bird would be different if the two clocks ticked at different rates - but since the diving bird is a single incident then it is not the bird that changed but rather it was only the results of the two calculations that differed.

The observers' interpretation of the incident differs solely because of the difference in their respective clock's tick rate.

01101001
2007-Feb-16, 06:06 PM
can someone answer my question 2 posts up

45 minutes is too long to wait before asking for a response? I can only counsel patience here. Sometimes it takes even longer. Hours. Sometimes days.

Ken G
2007-Feb-16, 06:27 PM
Describe to me an instant?

If you look at my logic, you'll see that any definition of an "instant" that takes longer than my brain can form an image, is sufficient. Do you have a longer period in mind?

Ken G
2007-Feb-16, 06:29 PM
If time was changed (speeding up) then the clocks would just keep doing what they were programmed to do, not speed up time.

It's not clear what you are saying. Clocks measure time, definitively. Thus whatever time does, clocks do, because whatever clocks do, time does. See? What's interesting is that all clocks in the same reference frame agree, but clocks in different frames don't. As clocks measure time, we therefore say that time speeds up. Physics is, above all, a science about measurement.

2007-Feb-16, 08:58 PM
If you look at my logic, you'll see that any definition of an "instant" that takes longer than my brain can form an image, is sufficient. Do you have a longer period in mind?

So if it takes you .00001 seconds to form an image, that's an instant?

Let's see, if light travels 186,000 miles per second, and your "instant" is .00001 seconds, that means light travels 1.86 miles in .00001 seconds in your "instant", which is still 186,000 miles per second. How do you conclude light traveling 1.86 miles in .00001 seconds is an "instant in time", if it takes you .00001 seconds to form an image?

A lot of things can happen in the time interval of .00001 seconds. ;)

Ken G
2007-Feb-16, 09:16 PM
So if it takes you .00001 seconds to form an image, that's an instant?Where did I suggest that idea?

Let's see, if light travels 186,000 miles per second, and your "instant" is .00001 seconds, that means light travels 1.86 miles in .00001 seconds in your "instant", which is still 186,000 miles per second. How do you conclude light traveling 1.86 miles in .00001 seconds is an "instant in time", if it takes you .00001 seconds to form an image?OK, one more time, you may define an instant to be anything you like, and if it is shorter than .00001 seconds (if we accept that as the time to form an image), then you must agree with everything I said above. Yes?

A lot of things can happen in the time interval of .00001 seconds. Precisely. You might want to notice that this chain of reason started out in response to the idea that you can only "see" what has already happened. Nothing you've said calls that the least bit into question.

SeanF
2007-Feb-16, 09:25 PM
I missed this thread until now! :o

I just want to say something in regards to the OP. Really, you cannot "accelerate a frame" and you're just asking for confusion by talking about it like that. After all, a Relativistic reference frame includes a time axis, and accelerating it would mean the time axis changes over time (and not just the time axis, either - you'd have at least one spatial axis that changes over time)!

Now, what happens when a clock accelerates is that the clock changes frames.

When you're accelerating two clocks, you can do so so that they are still synchronized when they stop accelerating, but even then the concept of those two clocks throughout the experiment being in the "same frame" as each other at the "same time" is somewhat problematic, isn't it?

At any rate, bottom line, reference frames can't be accelerated. :)

2007-Feb-16, 09:34 PM
Again, MY point is that there is no "instant in time". If there were an "instant", that would mean objects in motion would be in a specific place at a specific "time". How could an object be in any one specific place at any one specific time while the object is in motion?

If an object is in motion, it travels a specific distance in a specific time interval. No matter how much you break the time interval and distance into proportionally smaller pieces, the object continues to travel a specific distance in a specific time interval. If there was such a thing as a "instant", that would mean the object was in a specific place at a specific time, which could never be if the object was in fact in motion. If the object was in a specific place at a specific time, the object was not in motion.

peteshimmon
2007-Feb-16, 09:56 PM
I was trying to check something after posting in
gravs excellent thread. And we can almost do the
experiment if I can have two atomic clocks with
a ten digit readout to one tenth of a nano
second and an empty railway carriage with
attached locomotive. The observer sits in the
middle of the carriage with optics allowing
him or her to read the two clocks at once. They
are set running at the same time and mounted at
each end of the carriage. The readings stay the
same. Then the train accelerates to 100mph. The
forward clock launches its light with the clock
reading. The light makes its own sweet way to
the middle of the carriage in its own time. The
frame of the carriage is going faster and faster.
so the light arrives at the middle a little
earlier than when the train was stationary. And
the rear clock light is delayed by an equivalent
amount. They therefore do not read the same.
But when the train slows down and stops they are
back to reading the same! Any errors here?
I must have juvenile understanding of the words
frame and synchronisation:)

grant hutchison
2007-Feb-16, 10:16 PM
How could an object be in any one specific place at any one specific time while the object is in motion?So where is it at a specific time, if not at a specific place? Nowhere? Everywhere?

Grant Hutchison

Ken G
2007-Feb-16, 11:34 PM
Now, what happens when a clock accelerates is that the clock changes frames.You mean changes inertial frames. But your interpretation of "reference frame" is not very GR friendly because it is limited to inertial frames, so it can only be used in special relativity. To me, more generally a reference frame is simply the frame of an observer, pure and simple, regardless of what else is going on. So observers never change reference frame-- they are always in their own reference frame, and they are always stationary. But they can use relativity to conceptualize what other observers would observe in their own frames. Indeed, that is what relativity is all about, because the physics is in the connections between observers, because that's the only way we have to know what's happening nonlocally-- to predict how we'll be affected by what's happening out there.

When you're accelerating two clocks, you can do so so that they are still synchronized when they stop accelerating In what frame?

but even then the concept of those two clocks throughout the experiment being in the "same frame" as each other at the "same time" is somewhat problematic, isn't it?No, simultaneity has a clear definition in the absence of true gravity, even when there is acceleration. (I'm not sure what happens when there's true gravity, I think it can get pretty weird.)

At any rate, bottom line, reference frames can't be accelerated.In one sense that's true, because a reference frame is always stationary for the observer who defines that frame. Also, in special relativity, only inertial reference frames are included, so you are forced to move from one inertial frame to another. However, an observer can conceptualize someone else's frame that is accelerating by using a generalization to special relativity (which isn't really even general relativity if there's no gravity, there really isn't an official name for it), and that conceptualized frame can be accelerating or in a gravitational field.

Ken G
2007-Feb-16, 11:39 PM
Again, MY point is that there is no "instant in time". This is essentially an irrelevant philosophical musing. What in this thread is this observation relevant to? An instant is a physics device used in the treatment of time. It's philosophical standing is irrelevant both to how physics is done, and to the arguments in this thread about relativity. It is an interesting issue to ponder, certainly.

SeanF
2007-Feb-17, 01:24 AM
You mean changes inertial frames. But your interpretation of "reference frame" is not very GR friendly because it is limited to inertial frames, so it can only be used in special relativity.
Yes, I was thinking of SR only. mea culpa.

In what frame?
In their own frame - the one they're in when they've stopped accelerating. :)

No, simultaneity has a clear definition in the absence of true gravity, even when there is acceleration.
Yes, now that I've thought it through more, I see where I was falling off. :)

Sam5
2007-Feb-17, 01:44 AM
45 minutes is too long to wait before asking for a response? I can only counsel patience here. Sometimes it takes even longer. Hours. Sometimes days.

I agree. Sometimes I have to go out an get a hamburger while I'm thinking of a good answer to a question.

gGriffeth
2007-Feb-17, 01:55 AM
If two observers, each with their own clocks, time the diving of the birds then the two calculated speeds of the bird would be different if the two clocks ticked at different rates - but since the diving bird is a single incident then it is not the bird that changed but rather it was only the results of the two calculations that differed.

The observers' interpretation of the incident differs solely because of the difference in their respective clock's tick rate.
If your in the enterprise (for example) and i have my clock (with hands and it's powered by battery) and we hit light speed, my clock wouldn't know to start moving at a different rate. What I'm saying is that my clock has nothing to do with time itself, it just gives me a measurement of it. Do you understand what I'm saying?

gGriffeth
2007-Feb-17, 01:58 AM
Thus whatever time does, clocks do, because whatever clocks do, time does. See?
So if I turn the hands on my clock forward, well I accelerate through time?

gGriffeth
2007-Feb-17, 02:33 AM
I agree. Sometimes I have to go out an get a hamburger while I'm thinking of a good answer to a question.
Thanks to both of you, you've shown me the light.

Ken G
2007-Feb-17, 02:47 AM
So if I turn the hands on my clock forward, well I accelerate through time?

A "clock" is not something with a big hand and a little hand, it is something that measures time. The way to tell if something is a clock is if it performs the same function as the other things that are considered to be clocks. That's the only way to tell. When you find one, it will measure time, and whatever it does, is what time does. That is the definition of time, there isn't any other.

Squashed
2007-Feb-17, 04:36 AM
If your in the enterprise (for example) and i have my clock (with hands and it's powered by battery) and we hit light speed, my clock wouldn't know to start moving at a different rate. What I'm saying is that my clock has nothing to do with time itself, it just gives me a measurement of it. Do you understand what I'm saying?

According to my understanding of the concept called "time" every atom in the make-up of your clock will react to the velocity of the Enterprise.

Not just the atoms but every photon and packet of energy composing the clock must react to the velocity and change because of the velocity.

So, yes, your clock would "know to start moving at a different rate".

Study light-reflection clocks because these simple thought devices can lead to insights into the very essence of matter.

When a light-reflection clock is traveling at a velocity then the light bouncing back-and-forth between the mirrors must, by necessity, travel a longer path between the mirrors as compared with a similarly constructed, but stationary, light-reflection clock.

One might wonder how to tell which clock, of two, is actually stationary or most nearly stationary of the two - it is the clock that ticks the fastest.

And I agree that clocks have "nothing to do with time" because time is just a mental construct used for the purposes of predicting behaviors.

Clocks merely allow the observer to compare one process with another process.

01101001
2007-Feb-17, 04:39 AM
One might wonder how to tell which clock, of two, is actually stationary or most nearly stationary of the two - it is the clock that ticks the fastest.

To whom? Where?

RussT
2007-Feb-17, 09:20 AM
There is still a problem with simultaneity at ANY distance.

Ken G
2007-Feb-17, 03:47 PM
The "problem" is that one needs an arbitrary convention. So one is chosen (Einstein's), and you carry on. It's not so big a deal in SR.

gGriffeth
2007-Feb-17, 04:13 PM
According to my understanding of the concept called "time" every atom in the make-up of your clock will react to the velocity of the Enterprise.

Not just the atoms but every photon and packet of energy composing the clock must react to the velocity and change because of the velocity.

So, yes, your clock would "know to start moving at a different rate".

Study light-reflection clocks because these simple thought devices can lead to insights into the very essence of matter.

When a light-reflection clock is traveling at a velocity then the light bouncing back-and-forth between the mirrors must, by necessity, travel a longer path between the mirrors as compared with a similarly constructed, but stationary, light-reflection clock.

One might wonder how to tell which clock, of two, is actually stationary or most nearly stationary of the two - it is the clock that ticks the fastest.

And I agree that clocks have "nothing to do with time" because time is just a mental construct used for the purposes of predicting behaviors.

Clocks merely allow the observer to compare one process with another process.

That cleared things up a little. Thanks.

Squashed
2007-Feb-17, 04:33 PM
I was trying to check something after posting in
gravs excellent thread. And we can almost do the
experiment if I can have two atomic clocks with
a ten digit readout to one tenth of a nano
second and an empty railway carriage with
attached locomotive. The observer sits in the
middle of the carriage with optics allowing
him or her to read the two clocks at once. They
are set running at the same time and mounted at
each end of the carriage. The readings stay the
same. Then the train accelerates to 100mph. The
forward clock launches its light with the clock
reading. The light makes its own sweet way to
the middle of the carriage in its own time. The
frame of the carriage is going faster and faster.
so the light arrives at the middle a little
earlier than when the train was stationary. And
the rear clock light is delayed by an equivalent
amount. They therefore do not read the same.
But when the train slows down and stops they are
back to reading the same! Any errors here?
I must have juvenile understanding of the words
frame and synchronisation:)

Actually that might work.

I was trying to discover a way to determine whether a traveler can calculate their speed relative to the local speed of light in this thread: An Absolute Reference Frame (http://www.bautforum.com/showthread.php?t=47833); by using the spot sizes on the front and back wall of the spaceship - from the same spotlight.

It seemed like it had great potential until I learned about relativistic beaming.

The whole idea is clearer using the velocity of 0.8c because the light from the digital display takes 3 seconds to travel from the back clock to the observer whereas the light from the digital display only takes 1/3 second to travel from the front clock to the observe (using the layout (http://www.bautforum.com/attachment.php?attachmentid=3703&stc=1&d=1160488880) from my thread).

Even though the left side looks like it is 9 times farther away from the observer, the observer would be exactly in the middle between the two walls (or in this case digital clock displays).

We can ensure that the observer is exactly in the middle by using a round-trip light path to measure the distance between the two clocks because a round-trip light path is both a perfect clocking mechanism and a perfect meterstick.

peteshimmon
2007-Feb-18, 02:10 AM
I think I would prefer having the midpoint
scratched on the floor using a tape measure:)
Anyway no one has asked the obvious questions;
1) Is this right?
2) Do the readings stay different when the
acceleration ends?
3) Do the readings snap back to the same when
the acceleration ends?

Squashed
2007-Feb-18, 08:37 PM
I think I would prefer having the midpoint
scratched on the floor using a tape measure:)
Anyway no one has asked the obvious questions;
1) Is this right?
2) Do the readings stay different when the
acceleration ends?
3) Do the readings snap back to the same when
the acceleration ends?

If we really wanted to do the above experiment we would place the set-up on a rotatable platform with the clocks, one at the north and one at the south, which should result in the two displays reading the same to the observer.

Then rotate the assembly 90 degrees, so that one clock is at the west and one at the east, which should result in the clock displays being asynchronous.

We really do not need to put the clocks on a train - we'll just use the rotational velocity of the earth.

1.) Yes, I believe this is correct because it takes longer for the light from the display to catch up from the trailing clock than it takes for the light from the display of the leading clock to come back.

The time difference between the two clocks should remain fairly constant from day-to-day but there should be a annual variance due to the earth's motion around the sun, and the sun's rotation around the Milky Way.

2.) The readings will stay the same as long as there is a velocity.

3.) If the velocity that causes the difference ends then the clocks will read the same.

The difference is caused by velocity, acceleration just causes the velocity.

EvilEye
2007-Feb-18, 09:08 PM
Why make it so complicated?

Think of it as a frame in a film reel.

That image is a representation of everything in that frame at that instant. Even if it was in motion.

Or am I just confused?

peteshimmon
2007-Feb-19, 07:00 PM
I think there will be howls of rage from the
relativisists if anyone thinks you can detect
absolute movement in free fall by taking a
synchronised clock around the fra.. er cabin of
your spacecraft and noting when it differs
from the centre clock. Its the acceleration that
is detectable!

Squashed
2007-Feb-19, 07:57 PM
I think there will be howls of rage from the
relativisists if anyone thinks you can detect
absolute movement in free fall by taking a
synchronised clock around the fra.. er cabin of
your spacecraft and noting when it differs
from the centre clock. Its the acceleration that
is detectable!

Everyone measures the speed of light to be "c" by using a 2-way average but a stationary observer who measures the speed of light compared to the spaceship will note that the speed one way is c+v while the speed the opposite way is c-v (the observer is not measuring in the observer's frame but the traveler's frame). This is not against the mainstream because it falls out of the mainstream calculation.

We have never been able to directly measure the one-way speed of light but if your clock scenario works then we could calculate the one-way speed of light (or our speed as a fraction of "c").

Acceleration causes desynchronization of clocks but then so does distance.

If the observer, in the middle, sends a synchronizing signal, while moving, to the two clocks then both will have the same reading because that is a round-trip transaction which eliminates the one-way effects but if we synchronize and then add velocity the two clocks will appear to be asynchronous.

peteshimmon
2007-Feb-21, 07:56 PM
Actually I always understood the very first
speed of light measurement by Roemer using
variations in the occultation times of the Moons
of Jupiter was a one way measurement. I wonder
how accurate this method is these days.

01101001
2007-Feb-21, 08:03 PM
Everyone measures the speed of light to be "c" by using a 2-way average but a stationary observer who measures the speed of light compared to the spaceship will note that the speed one way is c+v while the speed the opposite way is c-v (the observer is not measuring in the observer's frame but the traveler's frame). This is not against the mainstream because it falls out of the mainstream calculation.

Please tell us more of this fascinating mainstream fact of anisotropic light speed. What is the best reference material to read to understand this?

Hey, in light of that, what corrections would you suggest for this page: What is the experimental evidence for the constancy of the speed of light? (http://www.perimeterinstitute.ca/Outreach/Education/Answer_1_-_The_Speed_of_Light/)

In 1964, scientists at CERN, a particle accelerator located on the Swiss-French border near Geneva, managed to create tiny subatomic particles called neutral pions and have them move at the speed of 0.99975c. These particles then emitted light in the form of gamma rays. Intuitively, we might think that the scientists in the lab would have measured the light’s speed to be 0.99975c + c = 1.99975c (i.e. the speed of the source plus c). But, observing it to within an accuracy of 0.1%, they found that it was c.

And their explanation of binary stars, how would you correct this, please?

The naive assumption of velocities c+v and c-v for light from stars A and B respectively would also mean that astronomers would see both orbits as being distorted and “out of synch” with each other. Such an observation would be incompatible with the constancy of c.

To date, astronomers have looked at thousands of binary systems. None of them has ever seen orbital distortions incompatible with the constancy of c. Moreover, what astronomers have observed strongly suggests that the speed of light is constant. The accuracy of at least one of these supporting experiments has been two parts in a billion.

Looking forward to it. Thanks.

Squashed
2007-Feb-21, 08:22 PM
Please tell us more of this fascinating mainstream fact of anisotropic light speed. What is the best reference material to read to understand this?

Hey, in light of that, what corrections would you suggest for this page: What is the experimental evidence for the constancy of the speed of light? (http://www.perimeterinstitute.ca/Outreach/Education/Answer_1_-_The_Speed_of_Light/)
...

I have never said that light speed varies, in fact I contend that the speed of light around blackholes remains at "c" even though the supposed dimension called "time" is greatly slowed and should thusly affect the apparent speed of light.

...

And their explanation of binary stars, how would you correct this, please?

...

Look at a light-reflection clock with the mirrors aligned to the direction of travel, the speed of light must measure "c" in the stationary frame in order for the stationary observer to be able to make sense of the situation.

But comparing the speed of light with the speed of the mirrors will give speeds that seem to make light speed variable, i.e.: c-v or c+v.

Take the neutral pion example because its speed is 0.99975c but when it self-destructs the light speed is 1.0c the difference between the pion speed and light speed is 0.00025c or 1.99975c (depending upon your reference direction). This measurement uses a moving reference point; whereas, a stationary observer measuring in the stationary frame uses a stationary reference point.

iM2L844
2007-Feb-21, 10:03 PM
The speed of light remains constant regardless of the velocity of your reference frame. If you are on a long (say 500,000 mile long) straight train moving with any constant velocity (say 500,000 miles per hour) and you are exactly the same distance from a light source at the front of the train and a light source at the rear of the train. if you could push a button causing both light sources to emit a beam of light toward you at the same time, the light from each source would reach you, or a clock, at exactly the same time. Say you were standing on a stationary platform next to the train and the light sources were mounted on the outside of the train, the light from each source would still reach you at exactly the same time. This is the heart of Lorentz invariance. Of course this all has to take place in a perfect vacuum which would make it very uncomfortable.
Also rates of acceleration can be directly calculated to have the same effect on time as gravity. Don't get acceleration and velocity confused. Hope this helps.

Time is that thing that keeps everything from happening all at once.

swansont
2007-Feb-21, 10:07 PM
I believe you're thinking of flying clocks around the world in opposite directions, and finding a time difference when they are reunited. One (the one travelling with the Earth's rotation) has travelled at a higher speed than the other.

Grant Hutchison

And in case you want to investigate it further, it's known as the Hafele-Keating experiment.

iM2L844
2007-Feb-22, 05:11 AM
I just wanted to point out that there have been some experiments done with mirrors in motion that have produced some anomalous results. Some of those are explained by Lorentz covariance; some others by quantum effects; still others that claim that they have not been properly addressed by SR at all. There have also been some experiments in the last few years where scientists, apparently, have been able to significantly "boost" the speed of light well past c. I'd have to copy and paste a whole bunch to try and pretend that I understand all that stuff...'cause I don't.

RussT
2007-Feb-22, 07:30 AM
I would be interested in seeing those.

Copy and paste away. Web addresses or specific papers.

iM2L844
2007-Feb-22, 08:08 AM
Cool...I'll round up some good ones in the morning, but I've go to get some sack time for now. The Ambien CR is kicking in.
Nick
Here's a pretty good one: http://www.iop.org/EJ/article/0295-5075/73/2/218/epl9119.html

Here's a less technical article on this paper: http://www.livescience.com/technology/060518_light_backward.html

Squashed
2007-Feb-22, 02:41 PM
The speed of light remains constant regardless of the velocity of your reference frame. If you are on a long (say 500,000 mile long) straight train moving with any constant velocity (say 500,000 miles per hour) and you are exactly the same distance from a light source at the front of the train and a light source at the rear of the train. if you could push a button causing both light sources to emit a beam of light toward you at the same time, the light from each source would reach you, or a clock, at exactly the same time. Say you were standing on a stationary platform next to the train and the light sources were mounted on the outside of the train, the light from each source would still reach you at exactly the same time. This is the heart of Lorentz invariance. Of course this all has to take place in a perfect vacuum which would make it very uncomfortable.
Also rates of acceleration can be directly calculated to have the same effect on time as gravity. Don't get acceleration and velocity confused. Hope this helps.

Time is that thing that keeps everything from happening all at once.

What you describe is a 2-way transaction which will always have the light reach you from both sources at exactly the same moment - but that does not mean that the one-way speed of light is the same in each direction (as measured using a moving reference point by an outside stationary observer).

The idea with the clocks in the O.P. has to do with the traveler discerning his speed (rather than just assuming himself stationary) within the range of zero velocity to "c" because it is within this range that every velocity must fall.

swansont
2007-Feb-22, 03:13 PM
I just wanted to point out that there have been some experiments done with mirrors in motion that have produced some anomalous results. Some of those are explained by Lorentz covariance; some others by quantum effects; still others that claim that they have not been properly addressed by SR at all. There have also been some experiments in the last few years where scientists, apparently, have been able to significantly "boost" the speed of light well past c. I'd have to copy and paste a whole bunch to try and pretend that I understand all that stuff...'cause I don't.

Anomalous dispersion effects need not apply for this position. It's neat stuff, but reshaping the pulse does not make anything actually exceed c that's forbidden from doing so. No causality violations.

iM2L844
2007-Feb-22, 06:46 PM
The idea with the clocks in the O.P. has to do with the traveler discerning his speed Well, maybe I misunderstood. Let's review the Opening/Original Post.

Am I right in stating that if two clocks are
synchronised in an inertial frame then that
synchronisation is lost if the frame is
accelerated along an axis through the
two clocks? They are separated by some
distance in the frame.

If the two clock are in the same inertial reference frame, they will both experience the same acceleration and velocity beginning and ending at exactly the same time. Their distance from one another would make no difference at all. They would remain synchronized throughout the trip. Is that better?

iM2L844
2007-Feb-22, 07:07 PM
Anomalous dispersion effects need not apply for this position. It's neat stuff, but reshaping the pulse does not make anything actually exceed c that's forbidden from doing so. No causality violations.Thanks, swansont. I just want to make it clear that I was not taking a position; I was merely pointing out ongoing arguments that teams with PHD's in various fields of Physics (people smarter than me) are engaged in.

Squashed
2007-Feb-22, 08:30 PM
Well, maybe I misunderstood. Let's review the Opening/Original Post. ...

Okay, you got me there because the original post is not exactly the scenario I was referring to which is this post: post #32 (http://www.bautforum.com/showpost.php?p=928452&postcount=32) where peteshimmon seems to clarify the intent (maybe the intent of the two posts are different) of the original post.

...

If the two clock are in the same inertial reference frame, they will both experience the same acceleration and velocity beginning and ending at exactly the same time. Their distance from one another would make no difference at all. They would remain synchronized throughout the trip. Is that better?

If the traveling observer between the two clocks sends a query to the two clocks then, yes, they will be synchronous because the query signal constitutes half of a round-trip communications link ... and a round trip measurement always results in both: a perfect clocking mechanism and a perfect meterstick.

But if the two clocks are synchronized by such a round-trip communications link while stationary and then the whole boxcar is put into motion then, with the digital displays continuously beaming to the traveling observer, the two clocks will appear to be asynchronous to the traveling observer between the two clocks.

For a light-reflection clock separated by 1.0 light-second and with the mirrors aligned along the direction of travel at a velocity of 0.8c then the light from the trailing mirror will take 3.0 seconds, as timed by a stationary observer, to travel to the leading mirror. In the opposite direction the light will take only 1/3 second, as timed by a stationary observer, to travel back to the trailing mirror.

Add the two times: 3.0 + 1/3 = 3.333 seconds

Since the stationary time between the two mirrors is: 1.0 + 1.0 = 2.0 seconds

then 2.0/3.333 = 0.6 which is the relativistic gamma factor for a velocity of 0.8c.

Without the ability to measure these seemingly different one-way light-speeds between the mirrors the traveler will have to assume that he is "at rest" but if the traveler can calculate his speed using the set-up as peteshimmon proposes then the traveler would know his velocity as a fraction of the speed of light.

At equatorial speeds (using the earth's rotational velocity) I calculated that the separational distance between the clocks, to get a 1.0 nanosecond of difference in the displays, would be about 186 miles (this could be wrong because I just cobbled together some MS Excel calculations).

So if we take two atomic clocks synchronize them and then move them apart at the same velocity/acceleration for each clock (but in opposite east-west directions) then we should be able to see a 1.0 nanosecond difference in the clock displays.

iM2L844
2007-Feb-22, 10:22 PM
hmmm, I didn't read all that into the original post, but when I consider your set up, I don't see where you've incorporated the gamma factor. I'm probably just overlooking something.

Okay. I went back and read post #32 and again c remains constant from each source for any observer regardless of the motion of the source or the motion of the observer ( t'= L/c) or if your light source is also at the center of the reference frame and "bouncing" beams of light of of mirrors at opposite ends of your frame of reference and back to the center then t' would equal 2L/c for each one. The clocks, in the same frame of reference, will read exactly the same. This is true even if the observer is a photodetector. You can't use Galilean transformations (v+c or v-c). Now, of course you're right, with regard to clocks in separate reference frames moving at different velocities. c will remain the same for all observers, but the clocks will tick at different rates. This was the genius of Einstein's realizations. Lorentz's crazy experimental observations weren't wrong as everyone, including Lorentz, had supposed. It was the distance and the rate of change in time that were actually changing; not the speed of light.

RussT
2007-Feb-22, 11:37 PM
Cool...I'll round up some good ones in the morning, but I've go to get some sack time for now. The Ambien CR is kicking in.
Nick
Here's a pretty good one: http://www.iop.org/EJ/article/0295-5075/73/2/218/epl9119.html

Here's a less technical article on this paper: http://www.livescience.com/technology/060518_light_backward.html

Thanks! The second one is blank.

EvilEye
2007-Feb-22, 11:38 PM
Could it just be that even though you would see the light coming back at the same time elative to your position, you would see one as blue and one as red?

01101001
2007-Feb-23, 12:27 AM
Thanks! The second one is blank.

With a URL including "light backward" it's probably the thing that's had several topics devoted to it:

Edit: I just checked the "blank" livescience site (http://www.livescience.com/technology/060518_light_backward.html). It initially rendered as nothing but a green field, but after 30 seconds or so, it eventually rendered the text and pictures. Give it time. It was the same stuff as many (or all) of those BAUT Forum topics: Prof. Boyd at University of Rochester. And it's not about photons moving faster than the speed of light, or moving backward in time, it's about the peak of a group of photons doing so. It's nothing revolutionary.

iM2L844
2007-Feb-23, 01:19 AM
Could it just be that even though you would see the light coming back at the same time relative to your position, you would see one as blue and one as red?That's exactly right, but only if the sources were moving toward or away from you. Not if they were stationary in your reference frame.

peteshimmon
2007-Feb-23, 06:59 PM
Hey! let me defend myself here. I asked the
original question as I was unsure if the
readings of the two clocks might show a
difference that is "ratcheted up" by any
acceleration and stays different when the
acceleration stops. Then deceleration (which
is acceleration in the opposite way) might
reset the clocks. I am now sure they snap back
to normal when the acceleration stops and show
an opposite difference on deceleration.
Actually you could use three clocks all set
together then walk two to each end of the
carriage. Then compared with the centre clock,
the other two will read slow by a few
nanoseconds. And a little bit of time dilation
caused by walking at 4 mph for 50 feet. You
try and work it out:)

EvilEye
2007-Feb-23, 07:32 PM
OK... well then. I would assume that the two (or 3) clocks and you were all in the moving car, and therefore would experience the same time dilation with movement.

You walking back and forth to check them would not create enough of a different to notice.

I suppose you would have to have giant clocks at either end and try to observe them at the same time from the middle to discern any change, but I suppose there wouldn't be any. The clocks would still read the same, because they are both moving in the same direction at the same time. The train isn't physically stretching with its minimal movement. Not discernable anyway.

Just my opinion.

Squashed
2007-Feb-23, 07:51 PM
Hey! let me defend myself here. I asked the
original question ...

WHAT !!! You're not gonna let me speak for you??? As your attorney I insist you remain silent while I do all the talking (PM me for instructions on delivering my fees).

I re-framed your question because it fit with an idea I was trying to prove which involves the travel time of light for a moving system.

According to the stationary observer the light must travel longer when reflecting from the trailing mirror to the leading mirror of a light-reflection clock.

Longer distances mean a disparity in clock readings ... but this should also be evident for accelerations because the principle is similar (without resorting to actual time dilation).

publius would be able to thoroughly enlighten us on the time dilational effects of accelerations - but he has not shown up, yet.

iM2L844
2007-Feb-23, 08:04 PM
peteshimmon, There is nothing to be defensive about. You asked a pretty straight forward question. The straight forward answer is: The clocks will remain synchronized exactly the same throughout acceleration and deceleration. There will be no snapping back into synchronization.

SharkByte
2007-Feb-23, 08:48 PM
It's not clear what you are saying. Clocks measure time, definitively. Thus whatever time does, clocks do, because whatever clocks do, time does. See? What's interesting is that all clocks in the same reference frame agree, but clocks in different frames don't. As clocks measure time, we therefore say that time speeds up. Physics is, above all, a science about measurement.

This brings up a question in my mind that, maybe the answer is already tehre but I'm just not getting it.

Do clocks actually measure time or are they simply a mechanically controlled visual representation of the passage of time? When I think of a device for the measurment of something I think of, for example a multimeter which can tell me the amount of current or voltage running through a wire. If I change the amount of current through an electrical system by adjusting a potentiometer the reading on the multimeter will change to reflect my adjustment. I can change the size of the gears in a clock to make the hands turn faster but that doesn't effect the actual speed of the passage of time. The "speed of time" stays the same from my reference point no matter what I do. This is kind of the problem I've always had understanding the twins aging thing too. I understand what the theory says I just can't put it all together to understand why it happens like that...

Squashed
2007-Feb-23, 09:15 PM
This brings up a question in my mind that, maybe the answer is already tehre but I'm just not getting it.

Do clocks actually measure time or are they simply a mechanically controlled visual representation of the passage of time? When I think of a device for the measurment of something I think of, for example a multimeter which can tell me the amount of current or voltage running through a wire. If I change the amount of current through an electrical system by adjusting a potentiometer the reading on the multimeter will change to reflect my adjustment. I can change the size of the gears in a clock to make the hands turn faster but that doesn't effect the actual speed of the passage of time. The "speed of time" stays the same from my reference point no matter what I do. This is kind of the problem I've always had understanding the twins aging thing too. I understand what the theory says I just can't put it all together to understand why it happens like that...

My view is that "time" is just a concept of the mind and that the three spatial dimensions are "real".

KenG aspires to view that "time" is real and the three spatial dimensions are just concepts of the mind (I hope I got it right).

My view says that clocks only compare one process to another, i.e.: the vibrations of cesium atoms to what ever process you are exploring (heartbeats, respiration??).

Others will have different views on this.

swansont
2007-Feb-23, 09:19 PM
This brings up a question in my mind that, maybe the answer is already tehre but I'm just not getting it.

Do clocks actually measure time or are they simply a mechanically controlled visual representation of the passage of time? When I think of a device for the measurment of something I think of, for example a multimeter which can tell me the amount of current or voltage running through a wire. If I change the amount of current through an electrical system by adjusting a potentiometer the reading on the multimeter will change to reflect my adjustment. I can change the size of the gears in a clock to make the hands turn faster but that doesn't effect the actual speed of the passage of time. The "speed of time" stays the same from my reference point no matter what I do. This is kind of the problem I've always had understanding the twins aging thing too. I understand what the theory says I just can't put it all together to understand why it happens like that...

Time dilation effects (both kinematic and gravitational) are NOT mechanical effects - they will happen the same for all clocks in any given situation, and this has been tested experimentally. However, there may be other effects, which would have to be separately accounted for (e.g. a crystal's reaction to acceleration, or the change in a pendulum clock under different values of g) that are mechanical effects. One has to distinguish between the two. The former are due to effects on time, and the latter are not.

EvilEye
2007-Feb-23, 09:36 PM
WOW!!!

Without all the math.... It would be pretty plain to see that on a train with clocks at either end, they would remain the same regardless of the outside world. The only difference would be the color of the light (if you could measure it) coming back from each clock to your eye.

If you were surfing on a wave, you could easily play catch with another person on the same wave with a ball. But a stationary person on a boat would never be able to catch it, because the ball would follow a curved tragectory if at the side of your wave.

iM2L844
2007-Feb-23, 11:32 PM
I understand what the theory says I just can't put it all together to understand why it happens like that... It's contrary to all common sense. If someone ever answers the question of WHY it happens like that, they will have accomplished Einstein's quest to understand the mind of God, but philosophy doesn't belong here.

My view is that "time" is just a concept of the mind and that the three spatial dimensions are "real". KenG aspires to view that "time" is real and the three spatial dimensions are just concepts of the mind (I hope I got it right).It would be interesting to know both of your views on causation. How does anything "happen" anywhere? Why don't I exist everywhere all at once?

If you were surfing on a wave, you could easily play catch with another person on the same wave with a ball. But a stationary person on a boat would never be able to catch it, because the ball would follow a curved tragectory if at the side of your wave. I hit a highway sign, with a beer bottle, out of a car window moving 60 mph once without much cypherin'. I don't know how to surf. LOL

Ken G
2007-Feb-23, 11:46 PM
It would be interesting to know both of your views on causation. How does anything "happen" anywhere? Why don't I exist everywhere all at once? This is why time is the fundamental physical observable, I argue. We have clocks, and a sense of time, and the rest is application. We can't actually measure distance, because all measurements are local, so to measure distance we have to actually move from the one point to the other, yet in our reference frame we are always in the same place. Hence, all measured distances are literally zero, but may be conceptualized to be something else for the purpose of doing physics. So what are we actually doing when we measure the distance from here to alpha Centauri, say? We are applying the laws of physics to make inferences about our local measurements, usually of light. Thus distance is a conceptualization, a creation of the human brain. All we really can actually measure is proper time. A metric is a way to convert from the proper time of an observer who was at two nearby events, to the conceptualizations of time and distance (i.e., unmeasurables) by an observer who was not at both events. The conceptualization allows how causality works in places where we are not, but the observer at both events is really the one who understands the causality-- when one event is the cause and the other is the effect. The fundamental "displacement" between a cause and an effect is the proper time between them, and metrics just allow other observers to do physics on that cause and effect, to anticipate how it might lead to effects that are at their location. Hence, time is real, and distance is pure conceptualization, on relativistic scales. (Around the house, the distinction is so minute that it makes no real sense to even draw it.) And what about spacelike displacements? They are actually imaginary proper times, which makes sense because they are precisely the events of which no clock can be at both.

iM2L844
2007-Feb-24, 12:53 AM
I guess that geometry class was a waste of...time.

Ken G
2007-Feb-24, 12:56 AM
Well put! And note that even geometry in relativity is the geometry of converting proper time into the concept of distance. So geometry is not a property of distance, it's the other way around-- the concept of distance is a property of the geometry, and the measured proper time. Don't get me wrong, you still need the conceptualization, just as you need the conceptualization of a "wave function" to do quantum mechanics. You just don't measure it.

Squashed
2007-Feb-24, 01:04 AM
...
It would be interesting to know both of your views on causation. How does anything "happen" anywhere? Why don't I exist everywhere all at once?
...

To begin with check out these two threads and maybe look at a few others started by me:

Good prep. discussion: An Absolute Reference Frame (http://www.bautforum.com/showthread.php?t=47833)

A 3 dimensional universe: Time Dilation - A Mechanical Defect (http://www.bautforum.com/showthread.php?t=50859)

KenG and I disagree but maybe someday I will see the universe as he sees it but right now I am stuck with just the three spatial dimensions.

After studying light-reflection clock scenarios my current conclusion is that apparent time dilation is just the slowing of energy processes within the structure of matter.

Just as velocity forces the light bouncing back-and-forth in a light-reflection clock to travel longer distances for each round-trip (which causes the clock to slow down); so, too, does velocity affect the inner workings of sub-atomic particles, atoms, molecules and ultimately clocks.

All clocks are similarly affected because all clocks and even living organisms share one common trait: we are made of atoms.

According to special relativity time slows down because of velocity. This slowing affect will slow down everything on the spaceship but here is an interesting difference between the view that "time" slows down and the opposing view that clocks just slow down:

The cosmic microwave background is isotropic (same everywhere) and so if "time" slowed down then so too would the absorbtion of CMBR but if you are traveling at 0.8c then your velocity will cause you to "collide" with a "cylinder" (a borehole through the CMBR) of that CMBR but simultaneously your metabolism will also be slowed by the velocity.

The result is you will experience less "clock time" but will experience more radiation. Without shielding you would end your trip with a burnt out and genetically mutated (caused by the blue-shifted CMBR) human body.

EvilEye
2007-Feb-24, 04:12 AM
Here's a thought. Like a black hole.

They keep saying that nothing can escape it, but they can detect them by the gamma rays exiting the poles of them.

Well if somthing is exiting from them, they must not be the end all, no?

Are Gamma rays faster than lightspeed?

RussT
2007-Feb-24, 07:55 AM
Here's a thought. Like a black hole.

They keep saying that nothing can escape it, but they can detect them by the gamma rays exiting the poles of them.

Well if somthing is exiting from them, they must not be the end all, no?

Are Gamma rays faster than lightspeed?

EvilEye, the jets exiting perpendicular to the plane of the galaxy out of the cores are coming from the 'accretion disc' that is formed 'outside' the event horizon of a massive black hole. Nothing can escape a black hole once it has passed the event horizon.

iM2L844
2007-Feb-24, 03:32 PM
Squashed, I would like to thank both you and Ken G. for taking the time to elaborate on your positions. I remain unmoved; which on the background of either of your cogitations would be exactly what is expected.LOL

Seriously, I wouldn't even try to belittle your Ideas but as long as matter exist and is changeable, I can't see the logic behind either view. Maybe it's because of years of using trigonometric functions for practical purposes. In my world view that's what makes perfect sense to me. On the other hand, I have had the experience of driving long "distances" at night when all of the sudden I would get the feeling that I was sitting still while the road was passing underneath me, but, man, that car was a smooth ride.

EvilEye, there are also huge blobs (many orders of magnitude larger than the earth) of plasma being ejected at 99.9% light speed from black hole "systems". RussT is right, there is a lot of stuff going on outside the event horizons (slingshot effect type stuff, etc.). It has been my opinion for a while that black holes really should be referred to as:"black hole systems"

Was the gamma ray question rhetorical? Gamma rays ARE light rays.

EvilEye
2007-Feb-24, 03:47 PM
Yes, my question was rhetorical, and I learned something from it.

I wasn't trying to change the subject either. I was trying to relate it to how if everything is in motion, we can ever have a real constant measurement.

Even in a lab, measuring light under the proper conditions, you can't stop the Earth from spinning, the solar system from moving around in the galaxy, or the galaxy from speeding throught the universe, and therefore.... how do we really ever know?

Time and space are impossible to accurately calculate, because every time you make an observation, the conditions on a larger scale change.

We may be able to guess, but 1 second later your best guess will be inacurate.

We use light-speed as a cosmological constant.... but we are the ones who measured it. ...while we were moving.

Now my brains are laying on the table in a puddle of mush. :wall:

iM2L844
2007-Feb-24, 06:46 PM
I was trying to relate it to how if everything is in motion, we can ever have a real constant measurement.You're in very good company, my friend. From Aristotle and Plotinus to Einstein, Hartle and Hawking this has been the nub of imaginable thoughts on this subject for more than two thousand years. Everything relates to something else. I've heard that someone has a theory about that. If a merry-go-round were the only thing in existence in an otherwise totally empty universe, how could you describe it's motion. Would it be spinning in space or would space be spinning around it? There would be no way to tell.

There is a pretty good book on this subject by Henning Genz called "Nothingness...The Science of Empty Space". I Just pulled it off the shelf and thumbed through it and here's a quote from it:

It remains to be admitted that to this day we don't have a convincing notion of why there is something, why not merely nothing;What"spiritus rector breathes fire into the equations and makes a universe for them to describe"?-raising the question, What do the laws of nature permit beyond what actually exists?

Now my brains are laying on the table in a puddle of mush. Judging from your avatar, this is not a totally foreign state of affairs for you...just kidding. Is that a bass guitar? I play a Strat and keep an F-150 in my living room.

swansont
2007-Feb-24, 08:32 PM
I wasn't trying to change the subject either. I was trying to relate it to how if everything is in motion, we can ever have a real constant measurement.

Even in a lab, measuring light under the proper conditions, you can't stop the Earth from spinning, the solar system from moving around in the galaxy, or the galaxy from speeding throught the universe, and therefore.... how do we really ever know?

So you do the experiments under different conditions. Constant results mean one thing, varying results mean another.

RussT
2007-Feb-25, 12:14 AM
RussT is right, there is a lot of stuff going on outside the event horizons (slingshot effect type stuff, etc.). It has been my opinion for a while that black holes really should be referred to as:"black hole systems"

[It has been my opinion for a while that black holes really should be referred to as:"black hole systems]

First, I agree with this 100%, and NO ONE understands the true deep connection that Non-Baryonic Dark Matter has to this 'system', especially to the MBH's, which is what we are really talking about here!!!

Second, [(slingshot effect type stuff, etc.)]this (as I am sure Publius would tell you, if he caught it) is a ECO/MECO prediction.

However, it is my contention that it DOES APPLY to a MBH 'system'. That is, that the 'double photosphere' ACTS as a hard/semi-hard surface and does allow for the aforementioned 'slingshot effect'.

peteshimmon
2007-Feb-25, 12:41 AM
I have been thinking it should be possible
using modern technology to build nanosecond
accuracy clocks to use in school physics labs
to try these ideas out. Three clocks with
circular displays showing nano seconds and
tens of nanseconds whirling around on bright
electronic displays. One or all clocks have
an optical switch pulsed from the 12 oclock
position of the nanosecond dial at a picosecond
pulse so that the display of another clock is
seen "strobed" at its time. All clocks are
set together for a synchronisation by some
means and then the fun can start. "Sir" can take
one clock and drive around for a few minutes
and come back showing the time dilation. It
might be possible these days! It seems no one
the moving carriage or I have missed it.

EvilEye
2007-Feb-25, 12:57 AM
"sir"'s nano clock would still not give you an accurate answer.

You are both moving throughout the universe withing a moving galaxy, within a moving solar system with a planet moving around a moving sun.

Your "nano" clock should be named a nono clock.

Clocks are only useful for our perspective time.

swansont
2007-Feb-25, 10:49 AM
I have been thinking it should be possible
using modern technology to build nanosecond
accuracy clocks to use in school physics labs
to try these ideas out. Three clocks with
circular displays showing nano seconds and
tens of nanseconds whirling around on bright
electronic displays. One or all clocks have
an optical switch pulsed from the 12 oclock
position of the nanosecond dial at a picosecond
pulse so that the display of another clock is
seen "strobed" at its time. All clocks are
set together for a synchronisation by some
means and then the fun can start. "Sir" can take
one clock and drive around for a few minutes
and come back showing the time dilation. It
might be possible these days! It seems no one
the moving carriage or I have missed it.

The technology exists to do this sort of thing (conceptually) but is not cheap. When my colleagues go to do a remote calibration of a two-way satellite timing station, they put some atomic clocks in a special SUV and drive there. A two-week trip (coast-to-coast and back) at normal highway speeds accrues a nanosecond or two of kinematic dilation. (at the remote locations, of course, you have to also account for gravitational changes and Sagnac effects). But cesium clocks are \$30-50k each, and you need several to do the kind of timing needed here, and then there is all the analysis hardware. Masers could work even better, but they start at about \$250,000, and those aren't really portable. And it still requires some nontrivial math to determine the time — no dial readout.

astromark
2007-Feb-25, 11:11 AM
This thread has thrashed this about back and forth and I think it has all been said. No not yet it would seem and now talking of clocks and time. They have very little in common. As stated back a few posts,. A clock does not measure time. It just gives us a method of definition of the when scale. There is no thing that is time. That undefined moment that is the present time has gone to become history. The past. While your eyes were still receiving that light that became a image. You can never measure the moment because it has gone. Just to drive this point home. Where did it go. There it is 186,000miles away in just one second. locked in to what is now history.

.

peteshimmon
2007-Feb-25, 01:06 PM
Thanks Swansont. I was thinking of some cheaper
technology that might give a clock accurate to
a nanosecond a week say, good enougth for
demonstrations on any one day. They would at
least show lightspeed in a stark way by moving
one clock away a few feet and viewing through
the optically switched eyepiece I tried to
describe showing its time lagging a few
nanoseconds. My error, I thought the atomic
clocks on jet planes experiment showed dilation
in microseconds allowing my suggested clocks
the possibility of showing smaller amounts.
That is quite a responcibility on your
colleages with the satellite timings. There are
hundreds of millions of SatNavs waiting to
take drivers up the wrong street!

swansont
2007-Feb-25, 01:17 PM
The Hafele Keating clocks-on-planes experiment resulted in a few hundred nanoseconds of difference, with the planes going an order of magnitude faster than an auto. The current clocks are better, which is why you can see the effect with the slower speeds, but we aren't ready for a "drive around the block" level of demonstration. Yet, anyway.

peteshimmon
2007-Feb-25, 01:33 PM
Ah pity! So many more threads like this then:):(

Squashed
2007-Feb-26, 02:48 PM
...

If a merry-go-round were the only thing in existence in an otherwise totally empty universe, how could you describe it's motion. Would it be spinning in space or would space be spinning around it? There would be no way to tell.
...

grav, had an interesting thought-experiment similar to this in which a geo-synchronous satellite was orbiting the earth but those were the only two bodies in the universe - how could we tell:

a.) If the satellite was moving?
b.) If the system was rotating?

Being geo-synchronous the satellite would sit apparently motionless in the sky (we'd have to shine a light on it to see it since there is no sun).

Since the orbital time matches the earth's rotation and we have no external reference points then how could we tell that we were rotating?

I suggest that by using atomic clocks we can tell because the atomic clock with the fastest tick-rate is the most stationary clock.

Clocks at the poles would tick the fastest and then there would be a gradient of slowing away from the poles with the slowest ticking clock being the one on the satellite (unless the tick rate was manually altered to sync with the earth surface clocks).

swansont
2007-Feb-26, 03:07 PM
grav, had an interesting thought-experiment similar to this in which a geo-synchronous satellite was orbiting the earth but those were the only two bodies in the universe - how could we tell:

a.) If the satellite was moving?
b.) If the system was rotating?

Being geo-synchronous the satellite would sit apparently motionless in the sky (we'd have to shine a light on it to see it since there is no sun).

Since the orbital time matches the earth's rotation and we have no external reference points then how could we tell that we were rotating?

I suggest that by using atomic clocks we can tell because the atomic clock with the fastest tick-rate is the most stationary clock.

Clocks at the poles would tick the fastest and then there would be a gradient of slowing away from the poles with the slowest ticking clock being the one on the satellite (unless the tick rate was manually altered to sync with the earth surface clocks).

"Most stationary" is not quite right - it would be "non-accelerating." The clocks would not tell you if you were moving through space at a particular speed. And whether the satellite was fast or slow depends on what orbit you choose. The gravitational dilation decreases as you go up, and this dominates at higher orbits. The break-even point is about 9500 km.

Rotation could be determined from the Sagnac effect, if you want to use clocks, or with a Foucalt pendulum.

John Mendenhall
2007-Feb-26, 05:55 PM
Cool...I'll round up some good ones in the morning, but I've go to get some sack time for now. The Ambien CR is kicking in.

Good refs, thanks.

John Mendenhall
2007-Feb-26, 06:09 PM
My invisible elf ??? Why he is made of dark matter and lives off of dark energy !!!

Wonderful, I love it!

John Mendenhall
2007-Feb-26, 06:19 PM
This thread has thrashed this about back and forth and I think it has all been said. No not yet it would seem and now talking of clocks and time. They have very little in common. As stated back a few posts,. A clock does not measure time. It just gives us a method of definition of the when scale. There is no thing that is time. That undefined moment that is the present time has gone to become history. The past. While your eyes were still receiving that light that became a image. You can never measure the moment because it has gone. Just to drive this point home. Where did it go. There it is 186,000miles away in just one second. locked in to what is now history.

.

True, all we observe has happened in the unreachable past. However, I think that synchronized clocks and simultanity can still be established. Remember the idea of a limit, as in calculus; we can, at least in theory, make the interval between observation of an event and reading the clock as small as we want, approaching zero as closely as we want.

Squashed
2007-Feb-28, 02:17 PM
...

Without the ability to measure these seemingly different one-way light-speeds between the mirrors the traveler will have to assume that he is "at rest" but if the traveler can calculate his speed using the set-up as peteshimmon proposes then the traveler would know his velocity as a fraction of the speed of light.

...

After thinking about this a while longer it would seem that the CMBR is a means for a participant to determine whether their reference frame is truly "at rest" or if their reference frame is in motion.

Since the CMBR is isotropic then two equal-sized spherical objects will both experience an equal number of CMBR photon strikes per unit of individual "clock time"; therefore, if one object's photon counter measures more photon strikes per second then that object is the least "at rest" object.

For instance if spherical object "A" is traveling at 0.8c then object "A" will recieve more CMBR photon strikes by the factor: 1/0.6

The factor is calculated by taking 1.0 divided by the gamma factor for the velocity 0.8c which is 0.6 and so the factor would be: 1/0.6 which equals 10/6 which equals 1.667

If object "B" is absolutely "at rest" then the factor difference between the two objects would be exactly 1.667 but if object object "B" is not absolutely "at rest" then the factor difference would be less than 1.667

The factor difference is the result of the moving clock ticking slower which allows more photon strikes per second than a stationary clock that ticks faster.

Or in other words the density of the CMBR would appear to be greater for the object that is actually moving with the greatest absolute velocity.

For the absolutely stationary object the CMBR density would be equal to 1.0 whereas the an object traveling at 0.8c would measure the CMBR density equal to 1.667

If time were an actual dimension then the CMBR density would always equal 1.0

grant hutchison
2007-Feb-28, 04:39 PM
After thinking about this a while longer it would seem that the CMBR is a means for a participant to determine whether their reference frame is truly "at rest" or if their reference frame is in motion.You're describing how one might find one's velocity relative to the CMB: if it appears a little hotter in one direction than in the opposite direction. An anisotropy of this kind is apparent in the Earth's sky, indicating our velocity relative to the CMB. It's another form of relativistic beaming. So the CMB doesn't determine an absolute rest frame, just a frame that we might find more interesting than many other possible reference frames.

Grant Hutchison

Squashed
2007-Feb-28, 07:26 PM
You're describing how one might find one's velocity relative to the CMB: if it appears a little hotter in one direction than in the opposite direction. An anisotropy of this kind is apparent in the Earth's sky, indicating our velocity relative to the CMB. It's another form of relativistic beaming. So the CMB doesn't determine an absolute rest frame, just a frame that we might find more interesting than many other possible reference frames.

Grant Hutchison

Grant, what you refer to is the various redshifting or blueshifting of the CMBR but this idea is more about photon counting, not the state of the photons.

I expound further in this post: Fried or Baked? (http://www.bautforum.com/showpost.php?p=935464&postcount=234)

The CMBR can be likened to a universal "quasi-atmosphere" and moving within that atmosphere is not without consequences, consequences which are measureable.

Measurements which, theoretically, would allow travelers to determine their relative motion with respect to each other - rather than the reciprocal motion arrangement of Einstein's.

grant hutchison
2007-Feb-28, 07:44 PM
Grant, what you refer to is the various redshifting or blueshifting of the CMBR but this idea is more about photon counting, not the state of the photons.The change in apparent black-body temperature of moving sources depends on both the Doppler shift and the change in photon count; I was referring to both effects when I used the word "hotter" with reference to the CMB seen under relative motion.

Measurements which, theoretically, would allow travelers to determine their relative motion with respect to each other - rather than the reciprocal motion arrangement of Einstein's.I don't understand how "relative motion with respect to each other" differs from "relative motion" or differs from Einstein's view.

Grant Hutchison

Ken G
2007-Feb-28, 07:55 PM
I think what Squashed is (incorrectly) arguing is that a problem with relativity emerges when you consider photon count, rather than redshift or energy flux. In the post he cites, he claims that the photon count is somehow preserved when you move relative to the CMB. Unfortunately, he does not support this contention with a calculation, and I wish to assure him that a correct calculation of what photon count does, per unit proper time (correctly transformed), obeys the requirements of relativity just fine. There's no fundamental difference between using energy flux or photon flux, the math just comes out a little different. Relativity works either way, and Grant is right that you can indeed measure a velocity relative to the CMB, and that does not violate relativity.

Perhaps part of the problem is the oft-repeated misconception that "relativity means there are no preferred reference frames". That statement depends quite sensitively on the meaning of "preferred"-- if you use the normal definition, "preferred by a scientist doing a calculation on the grounds that it makes it easier", then we prefer frames all the time in physics, even in relativity. All that relativity really says is that you are allowed to apply the same physics in any frame you like, it does not say that the universe will look just the same in any such frame, or that the calculation will be just as easy in any frame.

Squashed
2007-Feb-28, 08:08 PM
I think what Squashed is (incorrectly) arguing is that a problem with relativity emerges when you consider photon count, rather than redshift or energy flux. In the post he cites, he claims that the photon count is somehow preserved when you move relative to the CMB. Unfortunately, he does not support this contention with a calculation, and I wish to assure him that a correct calculation of what photon count does, per unit proper time (correctly transformed), ...

If my clock is ticking at half the rate of your clock then the number of photons I would count would be twice the number that you would count - but from your reference frame the count is normal because your time measurement is twice as long as mine ... so if I count 20 per hour then you would calculate that my 20 is for two of your hours which gives the usual 10 per hour that you have always measured.

The key is that my count per unit of "proper time" is different from your count.

btw: I did do a few calculations as this image shows: image (http://www.bautforum.com/attachment.php?attachmentid=4780&stc=1&d=1172695561)

For the Image:

Photon Flow is RED.
Traveler is BLUE.

In view 1 the photon flow is opposite the traveler's velocity.
In view 2 the photon flow is perpendicular to the traveler's velocity.
In view 3 the photon flow is the same direction as the traveler's velocity.

grant hutchison
2007-Feb-28, 09:29 PM
The key is that my count per unit of "proper time" is different from your count.So you will find that your velocity relative to the CMB is different from my velocity relative to the CMB. This is exactly what we'd expect for three reference frames in relative motion.

Grant Hutchison

Ken G
2007-Feb-28, 10:39 PM
If my clock is ticking at half the rate of your clock then the number of photons I would count would be twice the number that you would count - but from your reference frame the count is normal because your time measurement is twice as long as mine ... so if I count 20 per hour then you would calculate that my 20 is for two of your hours which gives the usual 10 per hour that you have always measured.

The key is that my count per unit of "proper time" is different from your count.That is just one of several issues that need to be kept track of to predict photon count rate, including how photon fluxes change with reference frame. Note that raindrop flux rates change with motion, it's not just relativity that does this. There are a myriad of net effects that all come in at order (v/c)^2, it's a bit of a mess to compute, but the total photon count will increase whether you use relativity or not-- a moving sphere of tissue paper in an isotropic rain saturates faster than a stationary one.

(edit: interestingly, this is even somewhat true if you only have rain coming from in front of you and behind you, never mind how-- if you run into one of those rains, it has no effect on the rate you get wet, until you go faster than the rain, at which point your wetting rate begins to increase.)

Squashed
2007-Mar-01, 02:28 PM
...

(edit: interestingly, this is even somewhat true if you only have rain coming from in front of you and behind you, never mind how-- if you run into one of those rains, it has no effect on the rate you get wet, until you go faster than the rain, at which point your wetting rate begins to increase.)

I'm not sure what you are saying by: "...if you only have rain coming from in front of you and behind you, ..." because it sounds like you are describing a rain that comes from two different directions, but maybe you are describing two different circumstances: one with rain from the front and one with rain from the rear.

When I did my "investigation" into the "rain" scenario (ever since Grant talked about rain in the relativistic beaming discussion) I only used rain traveling in one direction (there are 3 views each with a direction to the rainfall and travel).

Also, since the speed of light is the fastest that anything/entity can travel then there is no way to go faster than the photons (raindrops, for the rain analogy) so the "wetting" rate (reception rate of photons) will never increase due to velocity.

The reception rate for a particular direction can be influenced by a velocity in or against that direction but then the increased reception rate from that direction is exactly offset by a decrease in reception rate from the opposite direction.

For the CMBR there is no direction of flow because it comes at us from every direction - the only time it does not is when another body shields us from the direction towards that body. Since the CMBR "flows" at "c" in every direction then the reception rate remains constant for any and all velocities of the receiver.

The difference in reception, that I speak of, is due to the fact that the clock used to measure reception rate slows, the change in reception rate is NOT due to the actual rate of reception being changed.

So you state that "... the total photon count will increase whether you use relativity or not ..." but this does not apply to the CMBR because there is no way to go faster than the speed of light so the rate of reception always stays the same, but the perception of the reception rate changes due to the changing tick rate of the clocks.

grant hutchison
2007-Mar-01, 03:40 PM
Squashed, to get this straight you need to think about the clock rates a traveller will see in the sky as she moves relative to the CMB.
Clocks coming from ahead will look to be running fast; clocks departing astern will look to be running slow. Relativistic aberration gathers up clocks astern and makes them appear to be ahead, and so (when you do the maths) ends up packing more and more clocks into the "fast" section of the field of view ahead, despite the fact that this fast-clock region gets smaller and smaller (in angular terms) with increasing velocity. At the c limit, the whole Universe is apparently running infinitely fast, crammed into an infinitesimally small, infinitely bright spot dead ahead.
Now you can think of these clocks as photon sources, which will appear to emit more photons per second as they appear to run faster (and fewer as they appear to run slower). As increasing velocity packs more photon sources into the fast-clock region of the sky ahead, this more than compensates for the greatly reduced photon flux from the few, sparse photon emitters that still appear to be running slowly, astern. So the whole-sky photon flux rises with increasing velocity.

Grant Hutchison

Ken G
2007-Mar-01, 04:02 PM
I'm not sure what you are saying by: "...if you only have rain coming from in front of you and behind you, ..." because it sounds like you are describing a rain that comes from two different directions, Yes, the rain was coming from two directions at once (that's why I said "never mind how"!). It's just a toy problem, to begin the investigation of count rates, there's no relativity in it at all at this point.

Also, since the speed of light is the fastest that anything/entity can travel then there is no way to go faster than the photons (raindrops, for the rain analogy) so the "wetting" rate (reception rate of photons) will never increase due to velocity.That's true, I don't have any relativity in the rain problem. Note that when you include relativity, you don't just get the restriction that you can't go "faster than the rain"-- you also get a host of other correction factors that will require a very difficult calculation indeed. Such a calculation contradicts your statements, but so does the simpler nonrelativistic calculation, that's my point.

The reception rate for a particular direction can be influenced by a velocity in or against that direction but then the increased reception rate from that direction is exactly offset by a decrease in reception rate from the opposite direction.That is not true, not even when you don't have relativity, and it gets even less true when you have relativity. That's why I started with the rain simplification-- to show you the simplest possible case where it is false (when you run faster than rain). But if you let the rain come from more than two directions, or have more than just a single rain speed, any of those generalizations will make your statement no longer true. Relativistic corrections falsify it even more. There's just nothing left of it by then.

Since the CMBR "flows" at "c" in every direction then the reception rate remains constant for any and all velocities of the receiver.As I said, this is not true. The corrections come in at order (v/c)^2, like all relativistic corrections, and the "count rate" will also be modified in a fractional way proportional to (v/c)^2. The redshift, on the other hand, is order v/c, so that's what people normally notice when they talk about our velocity relative to the CMB. But that's not a relativistic correction, it's purely a time of flight effect on the perceived frequency.

The difference in reception, that I speak of, is due to the fact that the clock used to measure reception rate slows, the change in reception rate is NOT due to the actual rate of reception being changed.Here you are talking about relativistic (v/c)^2 corrections, so you are working at the order where I have shown your claims are untrue, even if you don't use relativity. If you do, the discrepancy only grows.

So you state that "... the total photon count will increase whether you use relativity or not ..." but this does not apply to the CMBR because there is no way to go faster than the speed of light so the rate of reception always stays the same, but the perception of the reception rate changes due to the changing tick rate of the clocks.I covered this above-- my statement stands.

Squashed
2007-Mar-01, 04:40 PM
...
That's true, I don't have any relativity in the rain problem. ...

Here you claim that I include relativity into the analysis by my mention of the speed of light but the universal maximum speed limit is not just a relativistic consideration - it is an inbuilt attribute to matter (and energy), there is no need to consider relativity to realize this.

...

That is not true, not even when you don't have relativity, and it gets even less true when you have relativity. That's why I started with the rain simplification-- to show you the simplest possible case where it is false (when you run faster than rain). ...

Again, since the rain is analogous to photons then I repeat it is not possible to go faster than the "rain" (speed of light) and so this point is not even necessary for consideration.

...
Here you are talking about relativistic (v/c)^2 corrections, so you are working at the order where I have shown your claims are untrue, even if you don't use relativity. If you do, the discrepancy only grows.
I covered this above-- my statement stands.

If relativistic effects can be explained by another understanding then why should I be constrained by the old relativistic calculations? As a relativist you must use these calculations to justify your perception but if relativity is not correct then your efforts are in vain.

You try to persuade me via relativistic lingo and I try to persuade you from my perspective. I see only clocks and metabolisms slowed by velocity whilst you see "time" slowed by velocity - in regular life there is little discernable difference but in "thought experiments" the difference can be quite distinguishable.

Ken G
2007-Mar-01, 05:17 PM
Here you claim that I include relativity into the analysis by my mention of the speed of light but the universal maximum speed limit is not just a relativistic consideration - it is an inbuilt attribute to matter (and energy), there is no need to consider relativity to realize this.

I know, what I'm saying is you are incorrect either way. Even very oversimplified problems demonstrate the flaw in your claim, and the full calculation only magnifies it-- that's what I'm saying.

Again, since the rain is analogous to photons then I repeat it is not possible to go faster than the "rain" (speed of light) and so this point is not even necessary for consideration.Not "necessary", but "illuminating". If you don't find it illuminating, disregard it, but you are still just as wrong in the argument you are presenting.

If relativistic effects can be explained by another understanding then why should I be constrained by the old relativistic calculations? As a relativist you must use these calculations to justify your perception but if relativity is not correct then your efforts are in vain.So you don't understand the technique of simplifying a problem by replacing it with a toy problem, to build understanding of some of the key issues that appear in the full problem? Then I cannot help you, except to say, if you insist, do the full calculation, and your conclusion is still wrong.

You try to persuade me via relativistic lingo and I try to persuade you from my perspective. I'm letting you pick your own level of complexity-- your conclusion is wrong at every level except the very "bottom rung" of nonrelativistic, constant-speed rain coming from only two opposite directions with motion slower than that single rain speed. In any other context, the count rate depends on receiver motion to order (v/c)^2, where c is the characteristic speed of the "rain", be it relativistic photons or nonrelativistic water droplets. That's all I can tell you, if you don't believe me you will have to do the calculation to prove it to yourself, or just go on being wrong. Your choice.

I see only clocks and metabolisms slowed by velocity whilst you see "time" slowed by velocity - in regular life there is little discernable difference but in "thought experiments" the difference can be quite distinguishable.Now we have the separate issue "what is time". You may adopt any philosophical definition you like, but in physics, the definition must be measurable (in principle, even in "thought experiments"!). Thus in physics, there is only one meaningful definition of time, and it is exactly that which clocks and metabolisms respond to. Indeed, the key thing to realize that makes time a useful concept is that all clocks and metabolisms in the same place and moving the same respond to "time" in the same way. Were that not true, there would be no concept of time in physics, it would simply not be an attribute of objective reality, or at the very least it would require modification that no current experimental result does require.

Squashed
2007-Mar-01, 05:34 PM
...

Now we have the separate issue "what is time". You may adopt any philosophical definition you like, but in physics, the definition must be measurable (in principle, even in "thought experiments"!). Thus in physics, there is only one meaningful definition of time, and it is exactly that which clocks and metabolisms respond to. Indeed, the key thing to realize that makes time a useful concept is that all clocks and metabolisms in the same place and moving the same respond to "time" in the same way. Were that not true, there would be no concept of time in physics, it would simply not be an attribute of objective reality, or at the very least it would require modification that no current experimental result does require.

The time issue is the crux of our opposing views for relativity claims that time has slowed greatly for a very fast moving object, say at 0.999999c, but the CMBR still continues to impact that object and at a higher impact rate (if I understand Grant's post correctly) and a more lethal strength (due to blueshifting) and precisely in a condition when the person's (I replace the object with a person) body can least defend against the onslaught, since the person's metabolism is greatly slowed; so time has not slowed for the traveler but instead only their clock and metabolism has slowed.

grant hutchison
2007-Mar-01, 05:49 PM
... but the CMBR still continues to impact that object and at a higher impact rate (if I understand Grant's post correctly) and a more lethal strength (due to blueshifting) and precisely in a condition when the person's (I replace the object with a person) body can least defend against the onslaught, since the person's metabolism is greatly slowed; so time has not slowed for the traveler but instead only their clock and metabolism has slowed.You seem to be very confused about what's going on, here. The increased photon flux I calculate from SR is measured in the observer's proper time. It's what they would experience if they moved relative to the CMB (or any other uniformly distributed sky-spanning source of photons, such as a skyful of stars). There's no "great slowing of metabolism" in their proper time.

Grant Hutchison

Squashed
2007-Mar-01, 06:00 PM
You seem to be very confused about what's going on, here. The increased photon flux I calculate from SR is measured in the observer's proper time. It's what they would experience if they moved relative to the CMB (or any other uniformly distributed sky-spanning source of photons, such as a skyful of stars). There's no "great slowing of metabolism" in their proper time.

Grant Hutchison

Are you saying that a traveler would see an increase in the photon density of the CMBR?

That is what I state in this post: CMBR (http://www.bautforum.com/showpost.php?p=936238&postcount=103); as a method for determining who is actually moving the most between two participants.

grant hutchison
2007-Mar-01, 06:08 PM
Are you saying that a traveler would see an increase in the photon density of the CMBR?Sure. More photons in the direction of travel, fewer from opposite the direction of travel, a net increase integrated over the whole sky. I've said that, Ken has said the same.

That is what I state in this post: CMBR (http://www.bautforum.com/showpost.php?p=936238&postcount=103); as a method for determining who is actually moving the most between two participants.Moving the most relative to the CMB; that's unsurprising, since you could do something similar with any two reference frames moving relative to a third. It doesn't help you find an absolute rest frame.

Grant Hutchison

Ken G
2007-Mar-01, 08:12 PM
so time has not slowed for the traveler but instead only their clock and metabolism has slowed.

I already explained to you the scientific definition of time, it is not a "disagreement". You can define your own meaning if you like, but you will not be able to measure it, and you'll have a hard time communicating with those who use a definition they can measure. See Grant's point about "proper" time.

peteshimmon
2007-Mar-01, 09:35 PM
If I might intrude on my old thread here, it
would be interesting to know if a measurement
of faint galaxies per square degree on a Hubble
deep field is slightly greater in the Leo
direction than the opposite direction. But I
suspect the error bar is too large for
something definitive.

Squashed
2007-Mar-03, 02:28 AM
If I might intrude on my old thread here, it
would be interesting to know if a measurement
of faint galaxies per square degree on a Hubble
deep field is slightly greater in the Leo
direction than the opposite direction. But I
suspect the error bar is too large for
something definitive.

Are you tryin' to take back control of the thread that I hijacked? We'll have to have a posting duel to determine who is really in control here!!!

- - - - - - - - - - -

When you say a "...measurement of faint galaxies per square degree on a Hubble deep field ..." what do you want to measure, i.e. the brightness, redshift, angular size, population?

peteshimmon
2007-Mar-04, 12:25 PM
Just numbers! As our "absoute" speed according
to the CMB is a fraction of 1% of c, it might
be possible if thousands of galaxies can be
counted in equivalent areas in these opposite
directions. And as to my original post way back
it seems no definitive answer has been put
forward! Perhaps still being thought about:)

Ken G
2007-Mar-04, 02:42 PM
The effect is too small to see that way. Unlike the asymmetry in the redshift, which is order v/c, the density asymmetry is order (v/c)^2. If our peculiar speed is 1/10,000 of the speed of light, the density effect is 1 part in 100 million. So even if we can count all the galaxies, of order 100 billion, the variance we'd expect fore/aft is only about a thousand galaxies different. The statistical variation in 100 billion is about 300,000, so the difference gets swamped.