TIME DILATION. WHY do clocks that are

[abbott287]

moving closer to light speed relative to another clock tick slower? I understand that the waves take longer to reach the stationary observer on the turn around, but that's just appearance. It still seems the clocks would be in sync upon the return. What is making time actually slow down (comparatively in that frame) by moving faster??

 

[HallsofIvy]

I'm not clear on what kind of answer you want. My reaction would be to say "that's the way the universe is". But you seem to want some kind of "mechanistic" answer.

 

[Janus]

It's a consequence of the speed of light being the same in all reference frames.

For example: Sam and Tom are have a relative speed with respect to each other. As they pass each other, they both set off a flash of light. According to Tom, both flashes of light travel away from him at c and he always remains at the center of the expanding sphere of light, while Sam moves away from the center.

However, according Sam, he is one that stays at the center of the sphere of light and its Tom that moves away from the center.

Now imagine that Tom and Sam have placed mirrors an equal distance apart, spaced perpendicular to their relative travel. According to each, the light pulse goes straight up, hits their mirror and comes straight down. This is one tick. But also, according to each, the light path follows a different path while traveling back and forth between the other person's mirrors. It must follow a longer diagonal path. since this light takes a longer path but travels at the same speed, it must take longer for the light to make the round trip. Thus according to Sam, his clock tick faster than Tom's, and according to Tom, his clock tick faster than Sam's

Something like this:

[URL]http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/time_dil.gif[/URL]

So according to each, nothing happens to his clock, but the other person's clock runs slow.

Okay, now why is it that, if one of them were to travel off, turn around and come back, that they would find that his clock has accumulated less time?

There are two other effects besides Time dilation to consider. One is length contraction. According to Tom a meter stick laying parallel to the relative motion and traveling with Sam will be shorter than his and vice versa.

So let's say that Sam travels off at 99% of c to a distance of 1 light year from Tom as measured by Tom and returns. According to Tom, this trip takes a little over 2 years. During which Sam's clock runs 1/7 as fast as his and reads ~2/7 of a year on returning.

According to Sam, however, the distance measured as 1 light year by Tom is only 1/7 of a light year, and thus it takes him only ~2/7 of a light year to make the trip and he Returns to Tom with only 2/7 of a years ticked away on his clock, which agrees with the time that Tom expects to have ticked away on Sam's clock.

The third effect is the Relativity of Simultaneity, and it explains why even though Sam expects Tom's clock to tick more slowly than his while he is on his outbound and return trips, he finds that Tom's clock has ticked away more time upon his return.

Basically, events that are simultaneous to Tom, won't be for Sam, and vice versa.

So let's say that there is a clock sitting at that 1 light year mark that reads the same as Tom's clock according to Tom. According to Sam, as he travels outward towards this clock it will actually read ahead of Tom's clock by 48/49 of a year. The outbound trip takes 1/7 of year according to Sam, during which the clock at the turn around point ticks off 1/7 as fast and accumulates 1/49 of year reading 1 year upon Sam's arrival.

Now here comes the tricky part. In order for Sam to return to Tom, he has to change velocity. And when he does so, he changes reference frames from one going away form Tom to one heading towards Tom. So now, according to the Relativity of Simultaneity, it is Tom's clock that must read ahead of The turn around point clock, This means, that according to Sam, when he turns around, Tom's clock must "jump ahead" to read 1 & 48/49 year, and ticks away 1/49 year on the return trip to read 2 years upon Sam's arrival.

 

[ghwellsjr]

Janus, I really like your great animation. I wish I knew how to make animations like that which appear right on the webpage. I have had to use youtube for mine which makes them inconvenient to see.

I also like your explanations up until the last few paragraphs:

Basically, events that are simultaneous to Tom, won't be for Sam, and vice versa.

So let's say that there is a clock sitting at that 1 light year mark that reads the same as Tom's clock according to Tom. According to Sam, as he travels outward towards this clock it will actually read ahead of Tom's clock by 48/49 of a year. The outbound trip takes 1/7 of year according to Sam, during which the clock at the turn around point ticks off 1/7 as fast and accumulates 1/49 of year reading 1 year upon Sam's arrival.

Now here comes the tricky part. In order for Sam to return to Tom, he has to change velocity. And when he does so, he changes reference frames from one going away form Tom to one heading towards Tom. So now, according to the Relativity of Simultaneity, it is Tom's clock that must read ahead of The turn around point clock, This means, that according to Sam, when he turns around, Tom's clock must "jump ahead" to read 1 & 48/49 year, and ticks away 1/49 year on the return trip to read 2 years upon Sam's arrival.

Can you explain where you got these numbers from? I cannot replicate your results.

 

[Dale]

I understand that the waves take longer to reach the stationary observer on the turn around, but that's just appearance. It still seems the clocks would be in sync upon the return.

Actually, all of the relativistic effects like time dilation are what remains after you take "appearance" into account.

 

[Janus]

Janus, I really like your great animation. I wish I knew how to make animations like that which appear right on the webpage. I have had to use youtube for mine which makes them inconvenient to see.

The frame are drawn with POV-Ray, then assembled by a GIF animator (I use Animation Shop 3).

I also like your explanations up until the last few paragraphs:

Can you explain where you got these numbers from? I cannot replicate your results.

To be quite frank, I cheated a bit on those numbers. I knew what times each clock needed to read upon Sam's arrival, how long the trip took according to Sam and the fact that time dilation is reciprocal. Since it took ~1/7 of a year to make the trip according to Sam, reciprocal time dilation says that Tom's clock and the turn around clock run ~1/7 year on his clock equal ~1/49 year on the other clocks. Since the turn around clock must read ~1 year when Sam arrives, then it has to read ~48/49 of a year when Sam leaves Tom according to Sam.

That ~48/49 of a year is due to the Relativity of Simultaneity. In the rest frame of Tom and the turn around clock, both clocks read the same value. In Sam's frame, they differ by an time equal to

\frac{\frac{xv}{c^2}}{\sqrt{1-\frac{v^2}{c^2}}}

Where x is the distance between Tom and the turn around clock as measured by Sam and v is their Relative velocity.

At 0.99c, x = 0.1411 ly (1 ly length contracted)

Since the bottom half of the equation also equals 0.1411, this leaves us with

\frac{(1 ly)(0.99c}{c^2}

If I use 1 ly/yr for c, I end up with an answer of 0.99 yr as the difference between the two clocks.

So when Sam leaves Tom at 0.99c and Toms clock reads 0, according to Sam, the turn around clock already reads 0.99 yr.

Now according to Tom. it takes 1ly/0.99c = 1.01 years for Sam to reach the turn around point, so this is what the turn around clock reads when Sam arrives.

According to Sam, it take 1.01*0.1411 = 0.1425 years to complete the first leg of the the trip. During which time the turn around clock runs at a time dilated rate of 0.1411, and accumulates 0.020 years. 0.99 +.02 = 1.01 yr, meaning that the turn around clock reads the same upon arrival according to both Sam and Tom.

Now Sam turns around and heads back towards Tom. We will assume for eases sake that this happens instantly. Now he still finds himself at the turn around clock but with his velocity in the opposite direction. But since he is now heading towards Tom and away from the turn around clock, their roles, according to the Relativity of Simultaneity, are reversed. The difference in their times remain the same, but now it is Tom's clock that must read 0.99 yr later than the turn around clock.

One thing that everyone must agree to is that the turn around clock reads 1.01 yr upon Sam's arrival, turn around and leaving the turn around clock. So if the Turn around clock reads 1.01 years when Sam leaves it, and Tom's clock reads 0.99y later, then according to Sam, Tom's clock now reads 2 yr.

The return trip is a mirror of the outbound trip, with Sam experiencing 0.1425 yrs, and expecting Tom's clock to accumulate 0.02 yrs and reading 2.02 yr upon arrival.

 

[ghwellsjr]

Janus, I appreciate your expanded explanation but I'm still very confused. Are you considering just two clocks, both stationary with respect to Tom, one you call Tom's clock, colocated with Tom and the other one that is 1 ly away that you call the turnaround clock, correct? Sam doesn't have any clocks, correct? You are only explaining how Sam will analyze both of these two clocks that are stationary with respect to Tom during this scenario, correct?

 

[Naty1]

Halls of Ivy has the key idea as far as I am concerned.

It still seems the clocks would be in sync upon the return.

yes it does SEEM that way upon a first look...but that is classical not relativistic reasoning. Physics requires some new "logic" and ways of thinking. When traveling at high speed, who would have guessed space is shortened...and that space and time are interchangeable entities (in Lorentz transforms for example)??

It would also "seem" that particles can be measured (observed) with infinite precision subject to the cleverness our measuring devices, but that too is not how our universe works. And who would have guessed in the subatomic world that objects/particles have discrete not continuous values?? It's a crazy world!

 

[Janus]

Janus, I appreciate your expanded explanation but I'm still very confused. Are you considering just two clocks, both stationary with respect to Tom, one you call Tom's clock, colocated with Tom and the other one that is 1 ly away that you call the turnaround clock, correct? Sam doesn't have any clocks, correct? You are only explaining how Sam will analyze both of these two clocks that are stationary with respect to Tom during this scenario, correct?

Sam does have his own clock by which he can make comparisons

He makes two comparisons:

One is comparing the times on the two clocks at rest with respect to Tom. This comparison reflects the Relativity of Simultaneity. It depends on not only the separation of the two clocks, but also Sam's relative velocity(speed and direction) with respect to them

The other is the Rate at which these clocks run with respect to his own clock during the two legs of the trip. This comparison reflects time dilation and depends on only the relative speed between Sam and the other two clocks.

Here's the situation drawn up as space-time diagrams (I reduced the relative speed to 0.866c in order to keep the second pair of diagrams from being too stretched out, but the ideas are the same).

Here's The S-T diagram from the rest frame of Tom. T1 is Tom's clock, T2 is the clock at the turn around point and S is Sam's clock.

[PLAIN]http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/tom.gif

Here's the same scenario from Sam's rest frame during the outbound leg. The inset shows the details during the outbound leg and upon reaching turn around more clearly:


[PLAIN]http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/sam_out.gif

Notice the offset in times of T1 and T2

And here's what it looks like from the rest frame of Sam during the return leg. The inset shows events right after Sam has reversed direction to when he returns to Tom.

[PLAIN]http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/sam_back.gif

Notice that the time on T2 remains unchanged at this instant, but T1 now reads a later time.

 

[op684]

Noob here. Sorry for the stupid question. I tried many times to understand relativity but it seems my brain is like a black hole; it absorbs but it doesn't shine off.

Does this have anything to do with time passing slower when one does nothing and vice versa?

For example, Tom and Sam are in a room. Tom is playing a game on PlayStation 3, while Sam is staring at a wall. Tom is enjoying the game and doesn't notice as time passes. Sam however, is very bored staring at the wall, and every minute seems like an hour to him. After an hour, when Tom and Sam stop their activities, they face each other again. To Tom, it seems like "time flied", and only minutes passed. To Sam, it seems like many hours have passed.

In our uneducated simple reality though, according to an "outside observer at rest", only an hour has passed. But according to theoretical physics, Tom and Sam experienced time differently and therefore there is no "real" time, and Sam has aged by several hours while Tom by only minutes.

 

[HallsofIvy]

Noob here. Sorry for the stupid question. I tried many times to understand relativity but it seems my brain is like a black hole; it absorbs but it doesn't shine off.

Does this have anything to do with time passing slower when one does nothing and vice versa?

For example, Tom and Sam are in a room. Tom is playing a game on PlayStation 3, while Sam is staring at a wall. Tom is enjoying the game and doesn't notice as time passes. Sam however, is very bored staring at the wall, and every minute seems like an hour to him. After an hour, when Tom and Sam stop their activities, they face each other again. To Tom, it seems like "time flied"

"time flew". "Flied" is not a word.

, and only minutes passed. To Sam, it seems like many hours have passed.

In our uneducated simple reality though, according to an "outside observer at rest", only an hour has passed. But according to theoretical physics, Tom and Sam experienced time differently and therefore there is no "real" time, and Sam has aged by several hours while Tom by only minutes.

Where did you get that idea? No matter how bored Sam may be, no matter how long he may feel like he stood there, "theoretical physics" says that, since he and Tom were stationary relative to one another, he actually ages no more than Tom. How much time has passed is measured on a clock, not by "feelings".

 

[op684]

Where did you get that idea? No matter how bored Sam may be, no matter how long he may feel like he stood there, "theoretical physics" says that, sinc he and Tom were stationary relative to one another, he actually ages no more than Tom. How much time has passed is measured on a clock, not by "feelings".

It was my dumb attempt at demonstrating in a humorous way how everyday people unlearned in physics "understand" relativity. Pardon me.

On a serious note tho, relativity says time would "stop" if we were to approach the speed of light (hypothetically), and for light itself, time doesn't exist. But the speed of light is not infinite. It's only 300,000km/sec. So then it needs two seconds to reach a point at a distance of 600,000km. So how can there be no time at the speed of light? What am I missing?

 

[Dale]

On a serious note tho, relativity says time would "stop" if we were to approach the speed of light (hypothetically), and for light itself, time doesn't exist. But the speed of light is not infinite. It's only 300,000km/sec. So then it needs two seconds to reach a point at a distance of 600,000km. So how can there be no time at the speed of light? What am I missing?

https://www.physicsforums.com/showthread.php?t=511170

 

[HallsofIvy]

It was my dumb attempt at demonstrating in a humorous way how everyday people unlearned in physics "understand" relativity. Pardon me.

You got to be careful, people are liable to take you seriously!

On a serious note tho, relativity says time would "stop" if we were to approach the speed of light (hypothetically), and for light itself, time doesn't exist. But the speed of light is not infinite. It's only 300,000km/sec. So then it needs two seconds to reach a point at a distance of 600,000km. So how can there be no time at the speed of light? What am I missing?

You are not thinking "relatively". Light would take two second to reach a distance of 600,000 km relative to a person stationary with respect to the light. Of course, since the speed of light is the same relative to any observer, that would be true for any observer. In the frame or reference of light, if there were such a thing, it would take no time at all to go any distance. That is why we say that there cannot be a 'frame of reference' at the speed of light relative two any observer.

 

[cosmik debris]

The simple answer, if it is simple, is that clocks moving relatively follow different paths in spacetime. A clock measures this distance. It is similar to getting different odometer readings in your car if you take a different route to the supermarket.

 

[ghwellsjr]

Janus, in your first scenario, you has a speed of .99c which resulted in a gamma of about 7 or a time dilation of about 1/7. You then did some kind of calculation which resulted in squaring 1/7 to get 1/49.

In your second scenario, the speed was .866c for a gamma of 2 and a time dilation of 1/2. Where is the similar squaring of 1/2 to get 1/4?

 

[Janus]

Janus, in your first scenario, you has a speed of .99c which resulted in a gamma of about 7 or a time dilation of about 1/7. You then did some kind of calculation which resulted in squaring 1/7 to get 1/49.

In your second scenario, the speed was .866c for a gamma of 2 and a time dilation of 1/2. Where is the similar squaring of 1/2 to get 1/4?

Yes, but I just noticed that there was some errors when I wrote down the numbers.( for instance, where I have T1 = 0.284 it should be 0.288) So some of the other numbers might be a tad skewed.

The 1/4, as did the 1/49, come from the fact that time dilation is reciprocal.

Just as Tom measures Sam's clock as running 1/7 the rate of his own when they are moving at 0.99c with respect to each other, Sam measures Tom's clock as running at 1/7 the rate his own. Thus for every second that ticks away on his clock, he would expect 1/7 sec to pass on Tom's clock. Since we established that Sam measured measures 0.1425 yrs as having passed by his clock on the trip out, he would expect ~1/7 of that amount of time to have passed on Tom's clock.

This means that when Tom reads 1.01 yrs by his clock, then according to him, at the same time, Sam's clock reads 0.1425 yrs. Sam however, say's that when his clock reads 0.1425 yrs, at the same time, Tom's clock reads 0.020 yrs.

This is just another way in the Relativity of Simultaneity comes into play: "At the same time" is different for Tom than it is for Sam.

 

[Denius1704]

I have a few questions about the clock which is on the moving ship. What would happen if the clock is parallel to the ship instead of perpendicular? In this example i would remind you that special relativity says that no matter your speed the photon in that clock would still move at its constant speed so the same slowing effect that is seen in its perpendicular position could not be observed in a parallel position.

Also why do we consider that time itself is slowing down, instead of the mechanism of the clock changing? I mean if we change the wheel inside a mechanical clock to a bigger one then the arrow would start moving slower than with a smaller wheel, does that mean that we are effectively slowing down time just by changing the wheel? I fail to see the logic of a clock slowing down = time slowing down.

And finally you say that if the ship is moving at half the speed of light, then the beam from the stationary car would pass it by at "full" speed (its constant speed). Well i want to imagine that the car is moving at the speed of light as well, what would happen then? Would the beam still pass it by with the same speed?

It's just a few questions which I've been pondering for a while now. I'm not a physicist so the math of this escapes me, but i like to think that a logical explanation would be sufficient. Thanks in advance.

 

[Denius1704]

I have a few questions about the clock which is on the moving ship. What would happen if the clock is parallel to the ship instead of perpendicular? In this example i would remind you that special relativity says that no matter your speed the photon in that clock would still move at its constant speed so the same slowing effect that is seen in its perpendicular position could not be observed in a parallel position.

Also why do we consider that time itself is slowing down, instead of the mechanism of the clock changing? I mean if we change the wheel inside a mechanical clock to a bigger one then the arrow would start moving slower than with a smaller wheel, does that mean that we are effectively slowing down time just by changing the wheel? I fail to see the logic of a clock slowing down = time slowing down.

And finally you say that if the ship is moving at half the speed of light, then the beam from the stationary car would pass it by at "full" speed (its constant speed). Well i want to imagine that the car is moving at the speed of light as well, what would happen then? Would the beam still pass it by with the same speed?

It's just a few questions which I've been pondering for a while now. I'm not a physicist so the math of this escapes me, but i like to think that a logical explanation would be sufficient. Thanks in advance.

 

[HallsofIvy]

I have a few questions about the clock which is on the moving ship. What would happen if the clock is parallel to the ship instead of perpendicular?

What do you mean by this? What part of the clock is parallel to the ship?

 

[Dale]

Hi Denius1704, welcome to PF!

Also why do we consider that time itself is slowing down, instead of the mechanism of the clock changing?

Because all clocks of any kind also slow down. Experimentally there is no difference between all clocks slowing and time slowing.

 

[Denius1704]

What do you mean by this? What part of the clock is parallel to the ship?

The example with the clock of a photon going up and down perpendicular to the ship, i am asking what will happen if the photon in the clock was going left and right, or parallel to the ship?

Because all clocks of any kind also slow down. Experimentally there is no difference between all clocks slowing and time slowing.

I can slow down all kinds of clock while i am sitting here on Earth, but you won't say that i am slowing down time right? What i am trying to say is that there is an event happening that changes the mechanics of the clock and you are equating that event to time slowing down. Clocks measure time but do not equal time. Just because the mechanics of measurement change cannot instantly translate to time itself changing. Anyway the whole clock slowing down issue comes after the explanation of the photon clock issue otherwise there is no issue at all :)

 

[Mordred]

The example with the clock of a photon going up and down perpendicular to the ship, i am asking what will happen if the photon in the clock was going left and right, or parallel to the ship?



I can slow down all kinds of clock while i am sitting here on Earth, but you won't say that i am slowing down time right? What i am trying to say is that there is an event happening that changes the mechanics of the clock and you are equating that event to time slowing down. Clocks measure time but do not equal time. Just because the mechanics of measurement change cannot instantly translate to time itself changing. Anyway the whole clock slowing down issue comes after the explanation of the photon clock issue otherwise there is no issue at all :)

I'm having diffculty interpreting what you mean in this statement at first glance it sounds as if your saying that just because clocks slow down does not mean time is slowing down. If that's the case it does not cover changes of atomic decay observed in the atomic clocks used to prove the theory.

 

[Janus]

The example with the clock of a photon going up and down perpendicular to the ship, i am asking what will happen if the photon in the clock was going left and right, or parallel to the ship?

Something like this:

[URL]http://home.earthlink.net/~parvey/sitebuildercontent/sitebuilderpictures/length_con2.gif[/URL]

The distance between the "sideways" mirrors will be contracted as measured by the "stationary" observer. (If you were in the spaceship, you would measure the distance between these mirrors as being the same as the vertical mirrors

I can slow down all kinds of clock while i am sitting here on Earth, but you won't say that i am slowing down time right? What i am trying to say is that there is an event happening that changes the mechanics of the clock and you are equating that event to time slowing down. Clocks measure time but do not equal time. Just because the mechanics of measurement change cannot instantly translate to time itself changing. Anyway the whole clock slowing down issue comes after the explanation of the photon clock issue otherwise there is no issue at all :)

The point is that if you were in the space ship, would not not be able to notice anything amiss about the light clock. If you were "standing still" and measured 1 sec between ticks , by whatever means you choose, you would still measure 1 sec by that same method if you were "moving". In other words, there is no test you can make that will tell you if you are "moving" or not.

Someone else with his own identical light clock using the exact same method you use would also measure one tick of his clock to be on second. However, he will note that the light bouncing between your mirrors travels a longer path than the light between his. The interval that you measured as one second, he measures as being longer than a sec. If you and he have a relative velocity of 0.866c, he will count 2 sec for every second you count off.

It isn't really due to any effect that traveling at high speed has on your clocks, it has to do with the fact that observers moving relative to each other measure time differently.

 

[Dale]

Clocks measure time but do not equal time.

That is a philosophical position that you are entitled to take, but it is non-falsifiable so it is non-scientific. Since all clocks slow down you cannot perform any experiment which would distinguish between clocks slowing and time slowing. So as far as science is concerned time itself slows.

Think of it this way, you could explain the observations of EM-based clocks by assuming some sort of Lorentz-style aether and have clocks slow rather than time. But then how do you explain the time dilation of muon decay? Well, you could make an analogous mechanism that slows weak-force based clocks. But then how do you explain the time dilation of quark decay? Now you need a third mechanism that slows strong-force based clocks. But then how do you explain the time dilation of gravitational clocks? Finally you need a fourth mechanism that slows gravitational clocks. In addition, you need some sort of explanation about why all of these different kinds of clocks just coincidentally happen to slow at exactly the same rate.

Or you could explain the observations of all four types of clocks as well as explan why they all slow at the same rate simply by assuming that time slows. Occham's razor.

 

[Buckleymanor]

Since all clocks slow down you cannot perform any experiment which would distinguish between clocks slowing and time slowing. So as far as science is concerned time itself slows.

Would a pendulem or mechanical clock not run faster on the surface of the Moon, than a similar clock on Earth, due to differences in gravitational field strengths, rather than relatavistic effects or time speeding up.
You would be hard pushed to say that time runs a lot faster on the Moon than Earth because of this.

 

[Denius1704]

Thanks Janus for the extensive reply, i thought that that's what the sideways clock would look like as well :) The thing is that there is something that keeps on nagging me about the whole logic of this thing. For instance the light clock again (since that's the most comprehensive explanation as to why time slows down), and correct me if I'm wrong in the logic of it, but because more time is needed for the light to reach each tick of the moving clock, then more time is needed by the stationary observer to observe the reflection of it. And here is where you are saying that because the stationary observer has to count two times more between the reflected ticks then time is moving slowly, but here is where i am trying to say that, all that means in mechanical view is that the light needed a bit more time to reflect two ticks (because from the point of view of the stationary viewer the other one was moving). So in effect what i am trying to say is that the stationary observer is watching an illusion of time slowing down, instead of actual time slowing down, because as you say according to the moving observer time is passing by at the same rate as everywhere else.

I will also mention Occam's razor as DaleSpam did, because if we use the twin paradox problem here, the simpler explanation would be that they are both seeing an illusion of time slowing down, than actually both of them observing time slowing down for the other person.

As for the clocks, again i mention mechanics and yes it is actually a simpler explanation that certain forces and certain conditions make elements decay at different rates, it is actually quite logical. It is not about philosophy, i am just trying to think logically.

 

[Dale]

I will also mention Occam's razor as DaleSpam did, because if we use the twin paradox problem here, the simpler explanation would be that they are both seeing an illusion of time slowing down, than actually both of them observing time slowing down for the other person.

The simpler explanation you propose is not consistent with observation, because if they were both just seeing illusions then they would be the same age when they reunited. Occham's razor says to use the simplest explanation which is consistent with the observations, it does not justify your choice here.

It is not about philosophy, i am just trying to think logically.

It is about philosophy. SR fits the data, so does LET (the "clocks slow down" theory), so any choice between them is philosophical. The reason that SR is generally preferred is Occham's razor, and the fact that SR generalizes easily to all of the fundamental forces, whereas LET does not.

 

[Dale]

Would a pendulem or mechanical clock not run faster on the surface of the Moon, than a similar clock on Earth, due to differences in gravitational field strengths, rather than relatavistic effects or time speeding up.
You would be hard pushed to say that time runs a lot faster on the Moon than Earth because of this.

The principle of relativity says that identically constructed clocks all time dilate, it does not say that differently constructed clocks run the same. The gravitational field is an essential part of a pendulum clock, so a Moon pendulum clock and an Earth pendulum clock are not identical clocks. Similarly, atomic clocks depend on temperature, so a hot and a cold atomic clock are not identical clocks. You can find many other such examples.

 

[abbott287]

It isn't really due to any effect that traveling at high speed has on your clocks, it has to do with the fact that observers moving relative to each other measure time differently.

Thats the hard part. I totally understand why people would measure times differently, (The ball in motion moving farther from a side "still" F.O.R.) but its due to appearance. Why someone would actually age less and why the clocks would not be in sync upon return totally fail me.

 

[sisoev]

Similarly, atomic clocks depend on temperature, so a hot and a cold atomic clock are not identical clocks.

Make perfect sense.
Thanks DaleSpam :)

We can conclude now that clocks moving in gravitational field are not identical to clocks which are in rest in the same gravitational field (satellite clocks/ground clocks)
Also fast moving in gravitational field are not identical to the slow moving clocks in the same field.
Would that be correct to say?

About Denius1704 question:
What is he saying is that a stationary observer would see the ticking of a fast moving light clock as follows:
the tick starts closer to us and completes further far from our position.
The light from the clock needs time to travel to us in order to be observed from us, thus making the end of the tick to be observed as delayed because as a light signal it needs more time to travel to our position of observation.
In a simple math we can deduct the known speed of the moving object and we will get the correct timing which will be equal to the time in the clock frame of reference.

To make Denius point clearer I'd say that we will not only observe "longer" second, but the light which represents that second will be seen by us as red shifted.
This take us further to another conclusion: the different light frequency and wave length has something to do with the speed of the light for different observers, but just ignore this and let stay in the topic.

 

[Denius1704]

I just wanted to see what kind of answers someone with more knowledge in physics would give to certain questions i had. I expected more or less what i got. It's just that i don't understand how can scientists connect an abstract construct such as time together with a physical construct such as space and think that that is ok. When a theory has so many paradoxes then there should be something wrong with it. You have the twin paradox, you have the ladder-garage paradox, you even have a paradox as explained by one of your own members here where the resting space of a photon makes absolutely no sense. And yet, people still keep on insisting that there is nothing wrong.

Thanks for the answers again. I'm out of this conversation, i don't want to start meaningless argument where no one agrees with the other.

@Buckleymanor: Thanks for that example Buckley, it was a perfect one, even though DaleSpam did not fully understand your reasoning :)

 

[Dale]

the tick starts closer to us and completes further far from our position.
The light from the clock needs time to travel to us in order to be observed from us, thus making the end of the tick to be observed as delayed because as a light signal it needs more time to travel to our position of observation.
In a simple math we can deduct the known speed of the moving object and we will get the correct timing which will be equal to the time in the clock frame of reference.

The statement in bold is simply incorrect. All of the basic relativistic effects (time dilation, length contraction, relativity of simultaneity) are what remains after correctly accounting for the delay due to the finite speed of light.

 

[sisoev]

The statement in bold is simply incorrect. All of the basic relativistic effects (time dilation, length contraction, relativity of simultaneity) are what remains after correctly accounting for the delay due to the finite speed of light.

DaleSpam, I don't put in doubt your knowledge and authority as a Science Advisor in Physics Forums, but your answer is unsatisfactory.
Einsteins relativity comes from the assumption that the speed of light is finite and same for all observers.
From there comes the subject of this discussion with all the paradoxes we try to understand.

You should not use the finite speed of light as supporting argument if the result from this assumption is in argument.
Instead explain and make us understand why the delay due to the speed of the object is not taken in account?
Why no one mention and explain the red shift of the light clock in a moving object?
How is measured the speed of light and why is measured that way?
Is one photon considered as light or the frequency of the successive waves are what we call light?
If the different frequency means slower or faster approaching successive waves doesn't that mean that every next wave is slower or faster for the observer?
If YES why should we still insist that the speed of light is constant and finite for all observers in a vacuum?
Why you don't see the moon clock as identical with the one on the Earth, but in the same time you consider identical the clocks on the satellite with those on the ground?

Too many questions, but I think that all of them are of a big importance for this discussion.

Thank You, and please bear with those who are striving to understand the theory of relativity.

 

[Dale]

Einsteins relativity comes from the assumption that the speed of light is finite and same for all observers.

Yes, and all of the results are derived on the assumption of intelligent observers which can rationally account for the known finite speed of light. Time dilation remains even after doing so.

To confirm this, note that time dilation is independent of the direction of motion and depends only on the speed. In contrast, the time between receiving the signal from successive "ticks" of a clock does depend on whether the clock is getting closer or further. After you account for the clock getting closer or further and the changing delay time due to that then you find that the clock is time dilated.

Please narrow down your questions to the one or two you feel are most important. That is just way too many questions to pursue.

 

[Janus]

I just wanted to see what kind of answers someone with more knowledge in physics would give to certain questions i had. I expected more or less what i got. It's just that i don't understand how can scientists connect an abstract construct such as time together with a physical construct such as space and think that that is ok. When a theory has so many paradoxes then there should be something wrong with it. You have the twin paradox, you have the ladder-garage paradox, you even have a paradox as explained by one of your own members here where the resting space of a photon makes absolutely no sense. And yet, people still keep on insisting that there is nothing wrong.

None of the so called "paradoxes" are real paradoxes in that they represent any actual contradictions. They are all a result of using an incomplete treatment of Relativity.

In a way, they are the equivalent of the "round Earth paradox" in which people used to argue against the world being a sphere by saying that the people on the underside would fall off.

 

[Denius1704]

None of the so called "paradoxes" are real paradoxes in that they represent any actual contradictions. They are all a result of using an incomplete treatment of Relativity.

In a way, they are the equivalent of the "round Earth paradox" in which people used to argue against the world being a sphere by saying that the people on the underside would fall off.

And people supporting the round Earth theory kept on asking how come we never get to the end of the horizon or how come certain stars are doing funny movements in the night sky if the Earth was the center of the Universe. Paradoxes on both sides. The question is which side has more of them. Because i believe the rule of thumb would be, the more paradoxes a certain theory has, the less likely it is to be true.

 

[D H]

Because i believe the rule of thumb would be, the more paradoxes a certain theory has, the less likely it is to be true.

You are looking at relativity from the wrong perspective.

There are no true paradoxes in relativity. All of the so-called paradoxes result from trying to look at relativity with Newtonian expectations. Relativity is, as far as we know, an internally-consistent description of the universe. Newtonian mechanics is also a self-consistent description (as far as we know; underneath it all there is always the problem of Gödel's incompleteness theorems).

Science has to do something that philosophy and mathematics don't have to do: Science has to agree with reality. The ultimate paradox of science is when a scientific theory fails to agree with reality, and this is where Newtonian mechanics falls apart. It simply does not agree with reality in the realms of largish velocities (special relativity), largish masses (general relativity), and smallish distances (quantum mechanics). All experiments to date show that relativity does agree with reality.

 

[sisoev]

Yes, and all of the results are derived on the assumption of intelligent observers which can rationally account for the known finite speed of light. Time dilation remains even after doing so.

Ha-ha :)
I'll not be quite intelligent if agree with the assumption without questioning it.
I understand the idea of relativity, but it does not make sense to me in some of its points, which I already mentioned.

To confirm this, note that time dilation is independent of the direction of motion and depends only on the speed.

Sure.
I didn't say otherwise.

In contrast, the time between receiving the signal from successive "ticks" of a clock does depend on whether the clock is getting closer or further. After you account for the clock getting closer or further and the changing delay time due to that then you find that the clock is time dilated.

I already introduced my understanding that the "up-tick" of the clock will be seen with delay, because due to the speed of the clock it will by further far from us when riches the top of the clock.
The signal from the "up" tick will travel longer to us, because it is further away from the "bottom" tick.
The light, I said, will be red shifted.

If the clock travels toward us, we will see that the tick starts further away from us, and the "up-tick" will happen closer to us.
We can visualize it the same way like in the first case(moving away), except that the angle of the clock light will be opposite and we will see it as blue shifted.
(Who makes the animations here? Please show it to us ;) )
Hence the time is "delayed" in both moving objects.

Please narrow down your questions to the one or two you feel are most important. That is just way too many questions to pursue.

Thanks for giving me the chance to ask :)
For now, would you please clear out for me the above.
Is it correct that in both cases we will see respectively red and blue shifted light from the clock?
Do you agree that the "slow" second is a result from the difference in the distance from which we perceive the "down" and "up" tick (starting and ending points of the tick)?

 

[Dale]

Paradoxes on both sides.

SR has no genuine paradoxes, only things that students find confusing to learn. It is simply Minkowski geometry, which is entirely self-consistent.

 

[Dale]

Hence the time is "delayed" in both moving objects.

And that delay is accounted for in both moving objects. Even after accounting for that delay time dilation still remains.

Is it correct that in both cases we will see respectively red and blue shifted light from the clock?

Yes. The signal from a departing clock will be redshifted and the signal from an arriving clock will be blueshifted.

Do you agree that the "slow" second is a result from the difference in the distance from which we perceive the "down" and "up" tick (starting and ending points of the tick)?

No, it has nothing to do with perception. The perception delays are accounted for and the time dilation remains.

 

[sisoev]

And that delay is accounted for in both moving objects. Even after accounting for that delay time dilation still remains.

Yes. The signal from a departing clock will be redshifted and the signal from an arriving clock will be blueshifted.

No, it has nothing to do with perception. The perception delays are accounted for and the time dilation remains.

Well, for now I have the feeling that relativity leans too much on the way we set the things to be perceived.
The traveling clock for instance; it won't give time delay for the observer if it travels in circle around him and instead up-down it moves left-right.
I cannot imagine that left-right moving clock will stop showing time delay while making U-turn around the observer only because it went into a half circle.
It appears that the shape of the path is of a great importance for the time delay.

If your answer for the above is short and you have time, would you please explain, how it comes that the clock on the moon is not identical with the clock on Earth, but the clocks on the satellites are identical with those on the ground?

Thank You.

 

[Passionflower]

And that delay is accounted for in both moving objects. Even after accounting for that delay time dilation still remains.

Exactly true!

Yes. The signal from a departing clock will be redshifted and the signal from an arriving clock will be blueshifted.

In special relativity departing clocks will always be redshifted, approaching clocks are typically blueshifted but in some cases they may be redshifted!

It might be an interesting exercise to calculate the conditions for which an approaching clock will not show any red or blueshift at all. :)

 

[Dale]

approaching clocks are typically blueshifted but in some cases they may be redshifted!

Good point, and congrats on breaking 1k posts!

 

[Dale]

Well, for now I have the feeling that relativity leans too much on the way we set the things to be perceived.

Your feeling is incorrect. It is an unfortunate misconception that happens sometimes. I have noticed it more in students who are taught relativity via "thought experiments" rather than geometrically, but it can happen either way.

The traveling clock for instance; it won't give time delay for the observer if it travels in circle around him and instead up-down it moves left-right.
I cannot imagine that left-right moving clock will stop showing time delay while making U-turn around the observer only because it went into a half circle.
It appears that the shape of the path is of a great importance for the time delay.

The shape of the path is indeed of great importance for the time delay, but of no importance whatsoever for the time dilation. That is because, as I have stated multiple times, the time delay is accounted for.

If your answer for the above is short and you have time, would you please explain, how it comes that the clock on the moon is not identical with the clock on Earth, but the clocks on the satellites are identical with those on the ground?

I cannot explain that. AFAIK it is not correct. Could you describe why you believe this? Perhaps I can help explain.

 

[Buckleymanor]

The principle of relativity says that identically constructed clocks all time dilate, it does not say that differently constructed clocks run the same. The gravitational field is an essential part of a pendulum clock, so a Moon pendulum clock and an Earth pendulum clock are not identical clocks. Similarly, atomic clocks depend on temperature, so a hot and a cold atomic clock are not identical clocks. You can find many other such examples.

Makes sense though it is not quite perfect how do you distinguish between relatavistic influencies and gravitational ones.
A Moon, Earth, pendulem, mechanical, or atomic clock are all effected by gravity or acceleration how do you decide if the effect is due purely to time dilation.
How do you separate the two.

 

[sisoev]

Your feeling is incorrect. It is an unfortunate misconception that happens sometimes. I have noticed it more in students who are taught relativity via "thought experiments" rather than geometrically, but it can happen either way.

Ha-ha :)
I got your point here :)

The shape of the path is indeed of great importance for the time delay, but of no importance whatsoever for the time dilation. That is because, as I have stated multiple times, the time delay is accounted for.

Now, here I am a bit of confused and embarrassed.
My English semantics is not as good as I'd like it to be.
Do you mean that in the curve of the U-turn the time will not delay, but it will carry the dilation from the approach toward the observer?
If so, we will have to assume that a clock starting its path in the curve will be in sync with our clock until it gets out of it (the curve)
Extending that though, the moving clock will never differ from our clock if it stays in the circle.
In other words, the clock which is moving in a circle does not show and does not even give us the idea for a time delay.
(How would we conclude that time dilation happens.)
Yet, we accept the illusion of the departing clock and dismiss the firs.

My point with the U-turn was that in it we observe the other frame of reference without any difference in the distance for any part of that frame.
In that case we don't observe red or blue shift of the light and no time delay or dilation.
Once the red (or blue) shift appears we see time delay.
Do you take in account the shift of the light spectrum.
Because it appears like the light approaches us with different speed (seen in the different shift of the light) and therefore we "experience" time delay in the other frame.

I cannot explain that. AFAIK it is not correct. Could you describe why you believe this? Perhaps I can help explain.

I don believe anything. I try to follow the facts.
We don't say that the time on the Moon is moving slower because the pendulum moves slower there. We know that this is due to the gravity.
You said that "the pendulum on the Moon is not identical with the pendulum on Earth".
A clock which is moving is not identical to clock which is in rest and so on.
But relativistic physicist say that the time on the satellites is slower than on Earth because the satellite clocks move slower.
How do you explain that claim if the clocks on the satellites cannot be identical with the clocks on the surface of Earth?

 

[Dale]

Makes sense though it is not quite perfect how do you distinguish between relatavistic influencies and gravitational ones.
A Moon, Earth, pendulem, mechanical, or atomic clock are all effected by gravity or acceleration how do you decide if the effect is due purely to time dilation.
How do you separate the two.

The period of a pendulum is approximately 2\pi\sqrt{L/g} so the dependence is very explicit. The period of an atomic clock is proportional to (m/M)\alpha^4mc^2, so I am not aware of any dependence on gravity or acceleration. A mechanical clock could probably be constructed either way, but I don't know a general formula for mechanical clocks.

 

[Passionflower]

Good point, and congrats on breaking 1k posts!

Wow 1k.
Have not posted much lately, perhaps to the relief of some :) , perhaps I can find some more time to post more often.

 

[Dale]

Do you mean that in the curve of the U-turn the time will not delay, but it will carry the dilation from the approach toward the observer?

The delay is proportional to the distance (delay=dist/c). Assuming that the U-turn maintains a constant distance to the observer then there is a delay, but it is constant during the turn. Despite the fact that the delay is not changing, time dilation is observed. This is known as the transverse Doppler effect, and has been experimentally measured.

Extending that though, the moving clock will never differ from our clock if it stays in the circle.
In other words, the clock which is moving in a circle does not show and does not even give us the idea for a time delay.

This is not correct. As I said above, this has been experimentally measured. Both with the frequency of emitted radiation as well as with the lifetime of unstable particles. I.e. both clocks based on EM and clocks based on the strong and weak nuclear forces demonstrate time dilation.

My point with the U-turn was that in it we observe the other frame of reference without any difference in the distance for any part of that frame.
In that case we don't observe red or blue shift of the light and no time delay or dilation.

Again, incorrect. We do observe a redshift.

I don believe anything. I try to follow the facts.

Excellent, here are the facts:
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

You will want to pay special attention to section 4.

How do you explain that claim if the clocks on the satellites cannot be identical with the clocks on the surface of Earth?

I recommend that you learn special relativity before trying to learn general relativity. For now, let's avoid situations with gravity.