## What the heck is Time?

Discussions on classical and modern physics, quantum mechanics, particle physics, thermodynamics, general and special relativity, etc.

### Re: What the heck is Time?

In order to compare cloks, the clocks must be in the same frame. If they're in the same frame, you are not measuring reciprocal time dilation, you are measuring relative aging which happens to be zero in your example. If they never stopped in relation to each other, they could have never compared clocks to determine reciprocal time dilation. The act of stopping has poisoned the experiment. The fact that they are now able to see that their Doppler shift ratio was reciprocal only means they had detected no relative aging going on. It does not mean they had detected reciprocal time dilation because in order to detect that, they would have never been allowed to stop. We're getting caught up in semantics again but my statement is precise.

Let's say Bob is the stationary frame and Alice was leaving at .6c. When Bob is 4 he sees Alice as 2 and a doppler shift ratio of 1/2. But that doesn't mean Alice is 2 when Bob is 4. Alice is 4 when Bob is 4 because there has been no relative aging going on between them. It also does not mean that Bob is 5 when Alice is 4 according to the time dilation formula of t=Yt' where t'=4 and Y=1.25.
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### Re: What the heck is Time?

P.S. I hope Dave can see I left him the answer to my question.
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### Re: What the heck is Time?

There is also the possibility that I have reworded the statement and lost its original meaning. Since I can't supply a link to such a Statement or Author, I will withdraw that statement.

(...!! )

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### Re: What the heck is Time?

Inchworm » 08 Feb 2017, 16:08 wrote:
Burt wrote:This scenario can only happen if the clocks are reciprocally time dilated as relativity requires. If we had an absolute frame for light, Alice and Bob would not have received identical Doppler-shifted signal on either side of the flyby.

Why not?

Because then the Doppler ratio would have been dependent not on their relative speed, but on their individual speeds relative to the aether, which is an unknown quantity. Remember that the speed of light is then not c relative to any of them, but only relative to the aether.

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### Re: What the heck is Time?

ralfcis » 08 Feb 2017, 16:25 wrote:Let's say Bob is the stationary frame and Alice was leaving at .6c. When Bob is 4 he sees Alice as 2 and a doppler shift ratio of 1/2. But that doesn't mean Alice is 2 when Bob is 4. Alice is 4 when Bob is 4 because there has been no relative aging going on between them. It also does not mean that Bob is 5 when Alice is 4 according to the time dilation formula of t=Yt' where t'=4 and Y=1.25.

The 'test for reciprocal time dialtion' that I have sketched has nothing to do with Alice and Bob comparing clocks, ever. They are forever purely inertial and is experiencing a flyby and is able to measure the Doppler ratio from the others transmitter. That's all. No need for any "stationary frame".

With a relative speed of 0.6c, time dilation per SR must be applicable and it must be reciprocal, otherwise Bob (and Alice) could not have observed twice the frequency when closing in on the flyby and half the frequency after the flyby. Go and try that numerically with an aether and no reciprocal time dilation - Galilean relativity is not hard to do...

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### Re: What the heck is Time?

Here is a snapshot out of Relativity 4 Engineers portraying Galilean relativity: Tx means transmitter and Rx means receiver. Speed is indicated by "dot x", meaning v/c and one can see how the speed of light can be less than 1 or more than 1, depending on in which direction the light is transmitted.

For the case portrayed, the wavelength received by the Rx is a factor $\Large\frac{1- \dot{x}_{Tx}}{1- \dot{x}_{Rx}}$ of that transmitted. This is simply the ratio of the speed of light relative to the Tx and the Rx.

Should we have swapped Rx and Tx around (i.e. light goes to the left), the wavelength received by the Rx would have been a factor $\Large\frac{1+ \dot{x}_{Tx}}{1+ \dot{x}_{Rx}}$ of that transmitted.

Let's return to Alice and Bob, armed with this information. To achieve a relative Galilean speed of 0.6c, we could arbitrarily have chosen Alice to have an absolute speed of 0.2c and Bob is chasing her at an absolute speed of 0.8c, for a difference of 0.6c.

If Bob is Tx and Alice Rx, she would have received a wavelength
$\large\frac{1- 0.8}{1- 0.2} = 0.25$ of Bob's transmitted wavelength.

Once Bob has passed Alice, his signal will have to go backwards to Alice and she would have received a wavelength
$\large\frac{1+ 0.8}{1+ 0.2} = 1.5$ of Bob's transmitted wavelength.

One can immediately see that the situation is no longer symmetrical like in the relativistic case, where the ratio before and after the flyby was just the inverse of the other, like half or twice the standard wavelength. It is also clear from this that the Doppler ratio observed will not be dependent on the relative speed between Bob and Alice, but rather on their individual speeds relative to a hypothetical aether.

What is observed in practice does not agree with this, but strongly favors the relativistic definition of no aether and that (in the absence of gravity) only relative speed influences the outcome.

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### Re: What the heck is Time?

Jorrie wrote:

"Each of them will view the others clock to run slow by the usual gamma factor, but here is no "clock differential" between them."

"PS: there are other methods, but they involve a grid with clocks for each of them and more difficult to explain."

"The 'test for reciprocal time dialtion' that I have sketched has nothing to do with Alice and Bob comparing clocks, ever."

Sorry I must have misunderstood. I thought my question was about an experiment where they could compare clocks. I meant clock readouts, not calculated clock readouts. Even though they can see the others doppler shift frequency and even a TV picture of the other clock running slow in the past before the crossing, they can't know what the other guy is seeing of their clock to say the time dilation is reciprocal at present. Yes they can say it was reciprocal in the past. The only time they can compare present clocks is at the crossover and their clocks will read identical at that point. I guess I'm splitting hairs because this point is important to my personal theory.

I will bend on one point though. Before Alice and Bob crossed and relatively stopped I said the stopping disqualified the test but it does not. The time period before a transition occurs IS reciprocal time dilation as you have said.

The Bob and Alice example I've included was to show the difference between comparing actual clock readouts and what the real calculated time is at a true present moment.
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### Re: What the heck is Time?

ralfcis » February 9th, 2017, 12:42 pm wrote:I will bend on one point though. Before Alice and Bob crossed and relatively stopped I said the stopping disqualified the test but it does not. The time period before a transition occurs IS reciprocal time dilation as you have said.

As I understand it, they never stop — they remain inertial all the time. They are at the crossing point for zero duration.
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### Re: What the heck is Time?

The transition between approaching and leaving is neither approaching nor leaving which means they are instantaneously stopped. This is the only way they can transfer clock info when their relative velocity is zero. Since they are side by side when this occurs, the speed of light delay is not a factor. If they had stopped relative to each other at a distance, you'd have to wait for the speed of light to cross that distance before you could claim an end to the spacetime interval.

Another way of looking at it is the doppler shift ratio switches from 2 to 1/2 and it must transition through a ratio of 1 in between. A ratio of 1 signifies they are stopped relative to each other.
Last edited by ralfcis on February 9th, 2017, 2:41 pm, edited 1 time in total.
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### Re: What the heck is Time?

I will bend on one point though. Before Alice and Bob crossed and relatively stopped I said the stopping disqualified the test but it does not. The time period before a transition occurs IS reciprocal time dilation as you have said.

I need to qualify it because although it is true for your example it is not true for the muon example and only partially true for the example of putting the earth between the two participants. They will experience reciprocal time dilation relative to each other but they will both experience relative aging relative to the earth.
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### Re: What the heck is Time?

BurtJordaan » February 9th, 2017, 12:44 am wrote:
Inchworm » 08 Feb 2017, 16:08 wrote:
Burt wrote:This scenario can only happen if the clocks are reciprocally time dilated as relativity requires. If we had an absolute frame for light, Alice and Bob would not have received identical Doppler-shifted signal on either side of the flyby.

Why not?

Because then the Doppler ratio would have been dependent not on their relative speed, but on their individual speeds relative to the aether, which is an unknown quantity. Remember that the speed of light is then not c relative to any of them, but only relative to the aether.
I repeat in case I could ameliorate my wording: for sound, doppler effect is due to the relative motion between source and observer, not to their motion with regard to air, so it should be the same for light if it was transmitted through a medium, thus if there would exist an absolute reference frame.

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### Re: Stop That!

ralfcis wrote:The transition between approaching and leaving is neither approaching nor leaving which means they are instantaneously stopped.

Ralf, surely you jest! Have you ever driven on a highway with a lot of oncoming traffic in the opposite lanes? Did you come to an "instantaneous stop" as you passed each one?

Two approaching vehicles with constant velocities maintain their relative velocity as they pass by each other. The word "approach" is commonly replaced with the word "separate" after they pass but that can cause confusion (because approach velocity = - separation velocity). If two cars each travel 60mph toward each other, they approach at 120mph, they pass at 120mph and then they separate (i.e. -approach) at 120mph. They never stop, but you already knew that!

At relativistic speeds velocity combination is a bit more complicated (assuring that neither vehicle sees the other exceed universal speed limit c). Nevertheless, no instantaneous stops are involved.

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### Re: What the heck is Time?

When 2 cars are going 60mph along side each other, are they relatively stopped? Moving and being relatively stopped are not mutually exclusive. Relative velocity seems to be the most misinterpreted thing in relativity because there are so many ways to misinterpret it that make sense.. All problems in relativity hinge around scenarios of leaving, stopping and approaching. A spacetime interval ends with a stop. When Alice returns to earth, the spacetime interval ends whether she blows by earth or lands on earth. Both are stops. Of course, maybe my interpretation is one of the wrong ones. But so far as I know, a comparison can't be made between clocks unless they're relatively stopped. So I can only logically conclude that when they blow by each other they are relatively stopped in the transition between approaching and leaving. Again, for an instant, their doppler shift ratio is 1 during the transition indicating a stop.
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### Re: What the heck is Time?

ralfcis » February 10th, 2017, 2:31 am wrote:When 2 cars are going 60mph along side each other, are they relatively stopped?

Yes – they are in the same frame. Alice and Bob are not.

When Alice returns to earth, the spacetime interval ends whether she blows by earth or lands on earth. Both are stops.

No, it is not a stop if she blows by earth. To be stopped (or relatively stopped) is to be stationary (or relatively stationary) for some minimal duration. An 'instant' will not do, as it has no duration. To be 'stopped' for (literally) an instant seems a contradiction in terms.

So I can only logically conclude that when they blow by each other they are relatively stopped in the transition between approaching and leaving.

I don't think so.

Again, for an instant, their doppler shift ratio is 1 during the transition indicating a stop.

My understanding is that the Doppler shift is never 1. No motion at all – hence no relative motion or Doppler effect – can take place in an 'instant'.
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### Re: What the heck is Time?

Inchworm » 09 Feb 2017, 23:16 wrote:I repeat in case I could ameliorate my wording: for sound, doppler effect is due to the relative motion between source and observer, not to their motion with regard to air, so it should be the same for light if it was transmitted through a medium, thus if there would exist an absolute reference frame.

No, unless I still read you incorrectly, you are wrong. Read this old thread's introduction on Doppler shift of sound. Its not the same as for light.

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### Re: What the heck is Time?

Positor » 10 Feb 2017, 06:52 wrote:My understanding is that the Doppler shift is never 1. No motion at all – hence no relative motion or Doppler effect – can take place in an 'instant'.

There is a "transverse Doppler shift" when two spaceships are at minimum separation during a flyby, caused purely by the reciprocal time dilation. This would actually the best direct test of the reciprocal time dilation, but more difficult to explain simply.

Since the overall Doppler shift must go from negative to positive in the flyby scenario, it must inevitably go through zero somewhere.

Things are complicated by the fact that the observed Doppler shift goes through zero (meaning a Doppler ratio of 1) somewhat before the point of minimum separation. This happens where the relativistic blueshift due to the radial component of the relative velocity vector cancels the redshift due to the transverse component of the relative velocity vector precisely.

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### Re: Grading on a Curve

ralfcis wrote:When 2 cars are going 60mph along side each other, are they relatively stopped?

Yes. They're at rest with respect to each other.

ralfcis wrote:A spacetime interval ends with a stop.

A line spatial line segment can be defined by its endpoints. In the same sense, a spacetime interval is a 4D separation having "events" (4D locations) as endpoints. If I measure a segment of your car's path on a highway, it doesn't necessarily mean your car stopped at the endpoints.

Velocities, by contrast, refer to the inclination of an objects worldline in spacetime, with respect to a particular observer's rest frame. Minkowski diagrams have time vertical and space horizontal, so velocity is actually the inverse of the slope of a worldline (to get meters per second).

ralfcis wrote:When Alice returns to earth, the spacetime interval ends whether she blows by earth or lands on earth. Both are stops.

Let's not confuse an object's worldline (it's path through spacetime) with a spacetime interval. A spacetime interval is the shortest path between two spacetime events.

If Alice decelerates to land on earth, she'll have a curved worldline, for which the slope represents her changing velocity. That worldline will be longer than the straight worldline that she'd have blowing past earth. Defining a segment of such a worldline doesn't indicate a "stop" of her vehicle, only a stop in our measuring of that segment.

ralfcis wrote:a comparison can't be made between clocks unless they're relatively stopped

If Alice takes a picture of her clock and Bob takes a picture of his, just as they pass, the images can be conveyed and compared as convenient. The images are "frozen" but the clocks run continuously. Anytime you glance at a clock, your eye is simply taking a picture.

ralfcis wrote: their doppler shift ratio is 1 during the transition indicating a stop

I see what you mean. However, the Doppler shift as they pass relates to the angle* of transmission being perpendicular to their parallel velocities at that point, not to their stopping. You would be correct, if instead of passing, they collided. Then, if the wreck sticks together, it would stop (they'd be in the same rest frame) and indeed the Doppler shift would then also be 1.

*The Doppler effect is determined from velocities and velocity vectors have direction.

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### Re: What the heck is Time?

Dave_Oblad » January 30th, 2017, 8:48 pm wrote:mitchellmckain:

Light, by convention, travels at about 300,000 Kps in flat space and vacuum.
If I have a race with light but can only travel half the distance to a given target that light has reached from a mutual starting line, then my speed must be about 150,000 Kps. Or 50% of Light Speed or 0.5 c.
Thus, my speed at 0.5 c (150,000 Kps) would be Relative to Light Speed, wouldn't it?

No matter how fast you travel, light will always be 300,000 Kps faster as you measure it. It is ONLY correct to say that you are traveling 0.5 c relative to your previous inertial frame or what you left behind such as the earth, it is definitely NOT relative to light speed -- that is nonsensical. To say that the 0.5 c is relative to light speed is as nonsensical as saying it is relative to your own speed.

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### Re: What the heck is Time?

BurtJordaan » February 9th, 2017, 11:54 pm wrote:
Inchworm » 09 Feb 2017, 23:16 wrote:I repeat in case I could ameliorate my wording: for sound, doppler effect is due to the relative motion between source and observer, not to their motion with regard to air, so it should be the same for light if it was transmitted through a medium, thus if there would exist an absolute reference frame.

No, unless I still read you incorrectly, you are wrong. Read this old thread's introduction on Doppler shift of sound. Its not the same as for light.
Here is what you said there about light:

Einstein finally came up with a solution: he replaced the ether with spacetime.[1] It is a new kind of 'ether', where time and distance become "private" to every inertial frame, with no need for any physical contraction. By this definition, Earth is stationary in "our new ether", where the locally observed speed of light is c, and Andromeda is stationary in "its new ether", where the locally observed speed of light is also c.

I think that the same reasoning with sound would give the same result, so I think that my argument still holds.

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### Re: What the heck is Time?

Inchworm » 10 Feb 2017, 16:19 wrote:I think that the same reasoning with sound would give the same result, so I think that my argument still holds.

Nope. The aircraft are not stationary in their "own air". And the speed of sound varies relative to the moving aircraft.
You should rethink...

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### Re: What the heck is Time?

The speed of sound does not vary more than the speed of light: both are independent from the motion of bodies. If we disregard the air, and if we consider one of the two planes to be at rest, then the calculations should give the same result. No need to do them, it's exactly the same reasoning.

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### Re: What the heck is Time?

False, Inchworm, false. I too was caught up on the same misconceptions you have. The speed of the source does not affect the speed of sound relative to the medium. The speed of the source can't push sound ahead of it any faster. The speed of the source gets converted into a change in frequency of the sound. All true. However, the speed of the receiver will affect the speed of sound relative to the receiver. This is not true for light. The speed of the source can also change the speed of sound relative to the source. The source can catch up to and overtake its sound. This is also not true for light. There are all kinds of permutations and combinations of determining the doppler effect for sound as opposed to the universality of the speed of light for all observers. For example, the relative speed of sound in an enclosed railcar as opposed to an open deck. What does light do if you turn it on in a long moving vacuum tube as opposed to sound in the same tube filled with air. My dissertation was so long and exhaustive, I gave up.
Last edited by ralfcis on February 10th, 2017, 12:12 pm, edited 1 time in total.
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### Re: What the heck is Time?

Hey fans, I just came up with the definitive definition of the nature of time in the personal theories section (the last 2 posts). I plan to clean up all derisive remarks towards relativity and any mentions of ralfativity and post the cleaned up version here since it's 100% derived from relativistic math. I hope, if there are any responses to this they do not include a dump of disjoint barely related facts (the type of responses physics forums tend to favor) and they do include a discussion of the interpretations and concepts gleaned from the math.
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### Re: What the heck is Time?

ralfcis » February 10th, 2017, 11:01 am wrote: The speed of the source gets converted into a change in frequency of the sound. All true. However, the speed of the receiver will affect the speed of sound relative to the receiver. This is not true for light.
This is not true for sound either, it will only change the frequency of the waves. We know it is so for sound since we can measure its waves with a faster than sound device.

The speed of the source can also change the speed of sound relative to the source. The source can catch up to and overtake its sound. This is also not true for light.
It is not because a plane can go faster than sound that it changes the way sound behaves, and we know it also: we know that sound will then form what we call a conical wave front.

There are all kinds of permutations and combinations of determining the doppler effect for sound as opposed to the universality of the speed of light for all observers. For example, the relative speed of sound in an enclosed railcar as opposed to an open deck. What does light do if you turn it on in a long moving vacuum tube as opposed to sound in the same tube filled with air.
Sound follows the air, so if it is entrapped in a railcar, it follows the railcar. Light doesn't follow the railcar because it is not entrapped in it.

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### Re: What the heck is Time?

Ok, I've tried.
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### Re: What the heck is Time?

Inchworm » 10 Feb 2017, 17:47 wrote:The speed of sound does not vary more than the speed of light: both are independent from the motion of bodies. If we disregard the air, and if we consider one of the two planes to be at rest, then the calculations should give the same result. No need to do them, it's exactly the same reasoning.

But the problem that we are discussing does not have any of the planes at rest in the air and we cannot discount the presence of the air.

Do you agree with the following statement? The planes will measure the speed of sound relative to them to depend on their speed through the air, but spaceships will measure the speed of light relative to them to be 'c' and independent of their speed relative to anything. We are talking inertial, non-accelerated motion, of course.

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### Re: What the heck is Time?

ralfcis » 10 Feb 2017, 18:10 wrote:Hey fans, I just came up with the definitive definition of the nature of time in the personal theories section (the last 2 posts). I plan to clean up all derisive remarks towards relativity and any mentions of ralfativity and post the cleaned up version here since it's 100% derived from relativistic math.

Hey Ralf, good show, and it is about time. ;) How many years now?

As long as you stick to the relativistic math and always come up with the right answers, it does not matter what interpretation you attach to it. If it works for you, it works.

This does not mean anyone else will understand or use your interpretation, though. In science, a "standard interpretation" has evolved and most scientists use it and hence can communicate with each other.

I have checked your last posts, but your interpretations may not enable communication with them, or with other readers, for that matter.

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### Re: What the heck is Time?

BurtJordaan » February 10th, 2017, 1:52 pm wrote:
Inchworm » 10 Feb 2017, 17:47 wrote:The speed of sound does not vary more than the speed of light: both are independent from the motion of bodies. If we disregard the air, and if we consider one of the two planes to be at rest, then the calculations should give the same result. No need to do them, it's exactly the same reasoning.
Do you agree with the following statement? The planes will measure the speed of sound relative to them to depend on their speed through the air, but spaceships will measure the speed of light relative to them to be 'c' and independent of their speed relative to anything.
If we have nothing faster than the speed of sound to measure sound, and if we cannot measure our speed through air, then I think that we will get the same result as for light: it would be impossible to know our speed with regard to air, so we would have to rely on a two way speed of sound. To measure our speed with regard to one another, we would thus have to decide which one of us is at rest, the same as for light.

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### Re: What the heck is Time?

I guess I'll add graphs. But nobody likes graphs. Maybe sock-puppets. Maybe in the form of a story the readers here can understand. See Alice run. Run Alice run. See Bob stay. Stay Bob stay. Nope I've already lost everyone.
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### Re: What the heck is Time?

Try "See Donald run, run Donald run". :0)

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