Are relativistic effects directional?

[TakenItSeriously]

We know that relativistic doppler effect is directional in terms of relative motion. That is to say that light becomes red shifted when it’s source is receding away from us while light becomes blue shifted if the light source is moving towards us.

But what about time dilation and length contraction? Could it be that time dilates only in a moving frame that is moving away from us? and that length only contracts in the sense of a frame that is moving towards us?

This was one of the important consequences I had mentioned in my explanation of the Twin Paradox which I had posted here:

In short, if you do the math, we can only say that from Bob’s perspective on Earth, time appears to be dilated due to relativistic redshift.

That is to say that if the light we are observing is a powerful radio transponder that pings at 1Hz, then from Bob’s perspective, he receives only 1 ping every 3 seconds due to relativistic redshift.

Now, this is not just due to time dilation because, as we know, relativistic redshift includes normal redshift plus the relativistic component based on the Lorentz transformation.

If we calculate time dilation alone at 80% of c the Lorentz factor (α) is 0.6 so time is only reduced to 60% of proper time.

That’s all well and good, but when we observe the ship on the return leg, Bob receives 3 pings per second! as if time were somehow speeding up in the moving frame which we know is not possible.

We already know that time dilation can never be speeding up beyond proper time and length contraction can never be expanding beyond proper length.

So what relativistic effect is responsible for this relativistic blue shift?

I would posit that length contraction is what causes the waves to compress beyond that due to normal blueshift.

Another words, we know that information must be conserved and of course waves are basically information. So we know that waves (or pings) cannot just be added to or removed from the streaming radio signal.

I know that the pings sent at 1 Hz are not waves but a composite of many waves but for all intents and purposes, we can think of them like light waves with a frequency of 1Hz.

We also know that the streaming radio signal is mostly still in the space between Earth and the ship as it approaches us as waves in space.

So my point is that if the distance between Earth in the approaching ship is length contracted, then so must be the wavelength of those waves.

The bottom line is that time dilation causes the relativistic redshift for receding light sources in terms of emitting fewer waves per second and length contraction causes the relativistic blue shift in terms of a shorter wavelength.

 

 

 

 

[Strange]

9 minutes ago, TakenItSeriously said:

But what about time dilation and length contraction? Could it be that time dilates only in a moving frame that is moving away from us? and that length only contracts in the sense of a frame that is moving towards us?

No, that is not what the theory says (and not what is shown by experiment). Time is dilated whatever the relative direction; in other words it is only related to speed, not direction. Length contraction occurs in the direction of motion (also unrelated to the direction relative to the observer).

[TakenItSeriously]

1 minute ago, Strange said:

No, that is not what the theory says (and not what is shown by experiment). Time is dilated whatever the relative direction; in other words it is only related to speed, not direction. Length contraction occurs in the direction of motion (also unrelated to the direction relative to the observer).

I agree, that’s what we learned in school but I’m positing something different and your reasoning is therefore circular.

[Strange]

1 minute ago, TakenItSeriously said:

I agree, that’s what we learned in school but I’m positing something different and your reasoning is therefore circular.

Then you need to show how this new theory can be derived from first principles and how it is supported by evidence.

My reasoning is not circular. It is simply a statement of fact.

!

Moderator Note

As you are proposing a replacement to Special Relativity I have moved this to Speculations. Please provide the required evidence to support your theory.

 

[TakenItSeriously]

1 minute ago, Strange said:

Then you need to show how this new theory can be derived from first principles and how it is supported by evidence.

My reasoning is not circular. It is simply a statement of fact.

This discussion is theoretically based not experimentally based. I don’t have the bank roll to fund an experiment of space ships that travel at relativistic speeds, not that we have the technology to do that anyway.

[Strange]

Just now, TakenItSeriously said:

This discussion is theoretically based not experimentally based. I don’t have the bank roll to fund an experiment of space ships that travel at relativistic speeds, not that we have the technology to do that anyway.

Well, you could show how your model is derived from first principles, as SR is.

And there is a mountain of data that confirms SR. You could try and explain why this does not falsify your idea.

 

Basically, we have a theory that has been well tested for more than a century. But you are now saying it is wrong, for no reason at all and with zero justification.

[TakenItSeriously]

I’m not contending that special relativity is wrong, only that our understanding of it is not fully realized.

Nothing in my post is inconsistent with the theory that Einstein discovered.

[Strange]

4 minutes ago, TakenItSeriously said:

I’m not contending that special relativity is wrong, only that our understanding of it is not fully realized.

Nothing in my post is inconsistent with the theory that Einstein discovered.

This: "time dilates only in a moving frame that is moving away from us and that length only contracts in the sense of a frame that is moving towards us" is inconsistent with SR.

It is not a matter of "understanding". It is not what the equations of SR say, and it is not what experiments show. Therefore, you are saying that SR is wrong in its predictions. And what you say is not consistent with experiment.

As you are unable to support your claims, I will request this thread is closed.

[swansont]

5 minutes ago, TakenItSeriously said:

I’m not contending that special relativity is wrong, only that our understanding of it is not fully realized.

Nothing in my post is inconsistent with the theory that Einstein discovered.

That doesn't jibe with "positing something different"

[TakenItSeriously]

13 minutes ago, swansont said:

That doesn't jibe with "positing something different"

As far as I’m aware, nothing in SR states that time dilation or length contraction is not directional. It’s only an intuitive assumption that it’s not.

Wouldn’t you at least agree that relativistic doppler effect is directional?

Edited November 25, 2019 by TakenItSeriously

[Janus]

1 hour ago, TakenItSeriously said:

We know that relativistic doppler effect is directional in terms of relative motion. That is to say that light becomes red shifted when it’s source is receding away from us while light becomes blue shifted if the light source is moving towards us.

But what about time dilation and length contraction? Could it be that time dilates only in a moving frame that is moving away from us? and that length only contracts in the sense of a frame that is moving towards us?

This was one of the important consequences I had mentioned in my explanation of the Twin Paradox which I had posted here:

In short, if you do the math, we can only say that from Bob’s perspective on Earth, time appears to be dilated due to relativistic redshift.

That is to say that if the light we are observing is a powerful radio transponder that pings at 1Hz, then from Bob’s perspective, he receives only 1 ping every 3 seconds due to relativistic redshift.

Now, this is not just due to time dilation because, as we know, relativistic redshift includes normal redshift plus the relativistic component based on the Lorentz transformation.

If we calculate time dilation alone at 80% of c the Lorentz factor (α) is 0.6 so time is only reduced to 60% of proper time.

That’s all well and good, but when we observe the ship on the return leg, Bob receives 3 pings per second! as if time were somehow speeding up in the moving frame which we know is not possible.

We already know that time dilation can never be speeding up beyond proper time and length contraction can never be expanding beyond proper length.

So what relativistic effect is responsible for this relativistic blue shift?

I would posit that length contraction is what causes the waves to compress beyond that due to normal blueshift.

Another words, we know that information must be conserved and of course waves are basically information. So we know that waves (or pings) cannot just be added to or removed from the streaming radio signal.

I know that the pings sent at 1 Hz are not waves but a composite of many waves but for all intents and purposes, we can think of them like light waves with a frequency of 1Hz.

We also know that the streaming radio signal is mostly still in the space between Earth and the ship as it approaches us as waves in space.

So my point is that if the distance between Earth in the approaching ship is length contracted, then so must be the wavelength of those waves.

The bottom line is that time dilation causes the relativistic redshift for receding light sources in terms of emitting fewer waves per second and length contraction causes the relativistic blue shift in terms of a shorter wavelength.

 

 

 

 

Relativistic Doppler shift is is a combination of Time dilation and classical Doppler shift effect.  The Classical Doppler Shift effect is simply due to the changing propagation time for the light due to the changing distance between source and receiver.

So in your example of a source approaching at 0.8c and having it light blue shifted by a factor of 3:

Start with a source 1 light hr from the receiver ( as measured by the receiver),  The source is sending out  signal at 1 hz (as measured at the source). 

Start with the leading edge of the first light wave.  It takes 1 hr to reach the receiver.

The tail end of the light wave will be emitted 1 sec later according to the source, and  1 2/3 sec later according to the receiver. In that 1 2/3 sec, according to the receiver, the source will have moved  1 1/3 light second closer.  Thus the tail end of the light takes 1 1/3 light sec less time to travel the distance between source and receiver.  Leaving 1 2/3 seconds later, and taking 1 1/3 sec less to make the trip means it arrives at the receiver 1/3 sec after the front end of the wave arrived. Since each successive wave follows immediately after the previous one, the receiver measures a frequency of 3 hz, compared the 1 Hz measured at the source.

Red shift just works the opposite way, with the distance increasing and the propagation times increasing. 

There is no need to invoke a "direction" factor to time dilation to explain relativistic blue-shift.

Time dilation and length contraction due to inertial motion do not have a direction component.

Relativity of simultaneity, and measurements made from a non-inertial or accelerating frame do.

 

30 minutes ago, TakenItSeriously said:

As far as I’m aware, nothing in SR states that time dilation or length contraction is not directional. It’s only an intuitive assumption that it’s not.

Wouldn’t you at least agree that relativistic doppler effect is directional?

It's right in the equation for gamma,   v is squared.     v stands for velocity, which combines both speed and direction.  Thus, moving in one direction you have v and in the other you have -v.

(-v)(-v) and (v)(v) give the same positive answer,  so neither time dilation or length contraction rely of the direction of v.

You have to use the same -v, +v convention when using the relativistic Doppler shift equation:

sqrt{{1-v/c}{1+v/c}}

Here v is not squared, so the stipulation is that v is positive if the source is receding, and negative if it is approaching.

Edited November 25, 2019 by Janus

[TakenItSeriously]

1 hour ago, Janus said:

Here v is not squared, so the stipulation is that v is positive if the source is receding, and negative if it is approaching.

Thanks for replying.

This is what I’m saying.

You need to assign a negative sign to the approaching direction which suggests directionality.

I will address your previous analysis shortly.

Edited November 25, 2019 by TakenItSeriously

[swansont]

1 hour ago, TakenItSeriously said:

As far as I’m aware, nothing in SR states that time dilation or length contraction is not directional. It’s only an intuitive assumption that it’s not.

Wouldn’t you at least agree that relativistic doppler effect is directional?

That's the wrong approach. There's nothing that says that it is. You have to assume something extra to put directionality into it.

The directionality of the doppler effect comes into play with the sign of v. The Lorentz factor uses v^2, so the sign goes away.

 

(edit: and now I see Janus has given a more complete answer than my short summary)

[TakenItSeriously]

1 hour ago, Janus said:

Relativistic Doppler shift is is a combination of Time dilation and classical Doppler shift effect.  The Classical Doppler Shift effect is simply due to the changing propagation time for the light due to the changing distance between source and receiver.

So in your example of a source approaching at 0.8c and having it light blue shifted by a factor of 3:

Start with a source 1 light hr from the receiver ( as measured by the receiver),  The source is sending out  signal at 1 hz (as measured at the source). 

Start with the leading edge of the first light wave.  It takes 1 hr to reach the receiver.

I agree that the relativistic component of relativistic redshift is caused by time dilation.That much seems to be logically self evident.

I don’t agree that time dilation can explain the relativistic component of relativistic blue shift.

Remember, time seems to be speeding up on the return leg and I think you would agree that time dilation never speeds up no matter how you look at it.

1 hour ago, Janus said:

The tail end of the light wave will be emitted 1 sec later according to the source, and  1 2/3 sec later according to the receiver. In that 1 2/3 sec, according to the receiver, the source will have moved  1 1/3 light second closer.  Thus the tail end of the light takes 1 1/3 light sec less time to travel the distance between source and receiver.  Leaving 1 2/3 seconds later, and taking 1 1/3 sec less to make the trip means it arrives at the receiver 1/3 sec after the front end of the wave arrived. Since each successive wave follows immediately after the previous one, the receiver measures a frequency of 3 hz, compared the 1 Hz measured at the source.

Baring time dilation, this analysis no longer has a causality attached to it.

I agree with your math but I would posit that the causality for it is due to length contraction not time dilation. i.e. wavelength is decreasing due to length contraction not that frequency is increasing due to time dilation.

Edited November 25, 2019 by TakenItSeriously

[Strange]

1 hour ago, TakenItSeriously said:

As far as I’m aware, nothing in SR states that time dilation or length contraction is not directional. It’s only an intuitive assumption that it’s not.

You are wrong. Time dilation is independent of direction. Length contraction happens in the direction of movement. That is defined by the mathematics of SR.

[TakenItSeriously]

7 minutes ago, swansont said:

That's the wrong approach. There's nothing that says that it is. You have to assume something extra to put directionality into it.

The directionality of the doppler effect comes into play with the sign of v. The Lorentz factor uses v^2, so the sign goes away.

 

(edit: and now I see Janus has given a more complete answer than my short summary)

Thanks, please refer to my reply to Janus.

6 minutes ago, Strange said:

You are wrong. Time dilation is independent of direction. Length contraction happens in the direction of movement. That is defined by the mathematics of SR.

I’ve never seen anything that shows that time dilation is independent of direction.

as far as length contraction goes, I agree. Length contraction does happen in the direction of travel. Not that length contraction happens in both the direction of travel and opposite to the direction of travel.

[Strange]

14 minutes ago, TakenItSeriously said:

I’ve never seen anything that shows that time dilation is independent of direction.

You just have to look at the derivation.

14 minutes ago, TakenItSeriously said:

as far as length contraction goes, I agree. Length contraction does happen in the direction of travel. Not that length contraction happens in both the direction of travel and opposite to the direction of travel.

That is not what you said originally. But that has nothing to do with the object moving towards or away from the observer. It happens in the direction the object is moving, which could be towards/away from (both are equivalent) the observer. Or any other arbitrary direction. 

Let's say the +ve Z axis is away from the observer and the -ve Z axis is towards the observer. The +X axis is to the right, -X to the left. +Y is up, -Y is down.

If the object is moving in either the +Z or -Z direction at 86% c, then it will be half the length in the Z axis.

If the object is moving in either the +X or -X direction at 86% c, then it will be half the length in the X axis.

If the object is moving in either the +Y or -Y direction at 86% c, then it will be half the length in the Y axis.

If it is moving in some other direction, then you just need to decompose it into the velocity vectors in each axis. 

[Janus]

12 minutes ago, TakenItSeriously said:

I agree that the relativistic component of relativistic redshift is caused by time dilation.That much seems to be logically self evident.

I don’t agree that time dilation can explain the relativistic component of relativistic blue shift.

Remember, time seems to be speeding up on the return leg and I think you would agree that time dilation never speeds up no matter how you look at it.

Baring time dilation, this analysis no longer has a causality attached to it.

I agree with your math but I would posit that the causality for it is due to length contraction not time dilation. i.e. wavelength is decreasing due to length contraction not that frequency is increasing due to time dilation.

with Relativistic blue-shift, you visually a higher frequency arriving from the approaching source, but that does not mean you conclude that time is proceeding faster for the source.

With classical Doppler shift, you also would see a higher frequency arriving from the approaching source but you would not conclude that time runs faster for the source, because once you factor out the decreasing distance effect, you would conclude that time runs at the same rate for the source as it does for the receiver.    With Relativistic Doppler effect, once you factor out the decreasing distance effect you are left with time dilation and events occurring slower at the source.

There are two components at play with Relativistic Doppler shift.  Time dilation, which always has the moving source clock tick slow, and changing propagation time , which invcreases for receding sources and decreases for approaching ones.

Do not conflate what a observers visually sees via the light arriving from a source with what that observer would conclude it happening at the source.

Length contraction plays no role, as this would involve comparing distance measurements made by the source and emitter. In the above analysis, we only have to deal with distance measurements made from the rest frame of the receiver to get the proper Doppler shift.

[TakenItSeriously]

3 minutes ago, Strange said:

You just have to look at the derivation.

That is not what you said originally. But that has nothing to do with the object moving towards or away from the observer. It happens in the direction the object is moving, which could be towards/away from (both are equivalent) the observer. Or any other arbitrary direction. 

Let's say the +ve Z axis is away from the observer and the -ve Z axis is towards the observer. The +X his is to the right, -X to the left. +Y is up, -Y is down.

If the object is moving in either the +Z or -Z direction at 86% c, then it will be half the length in the Z axis.

If the object is moving in either the +X or -X direction at 86% c, then it will be half the length in the X axis.

If the object is moving in either the +Y or -Y direction at 86% c, then it will be half the length in the Y axis.

If it is moving in some other direction, then you just need to decompose it into the velocity vectors in each axis. 

Who’s derivation? can you provide a link?

If I’m not mistaken, I believe the direction of travel quote was from Einstein himself. I cant recall exactly my source for this belief however length contraction is always stated in terms of the direction of travel.

I don’t think that Einstein was prone to making mistakes in hidden assumptions in language given the theory itself which is inundated with such intuitive traps.

 

 

[Strange]

Just now, TakenItSeriously said:

Who’s derivation? can you provide a link?

For example:

https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_velocity_time_dilation

and:

https://en.wikipedia.org/wiki/Length_contraction#Derivation

Quote

If I’m not mistaken, I believe the direction of travel quote was from Einstein himself. I cant recall exactly my source for this belief however length contraction is always stated in terms of the direction of travel.

I don’t think that Einstein was prone to making mistakes in hidden assumptions in language given the theory itself which is inundated with such intuitive traps.

As you can't remember the quotation or the source, I think it is more likely you have misremembered it than that the mathematics of SR is wrong.

[TakenItSeriously]

I’ll need some time to reply to this but will reply to Janus first.

In the mean time, how do you split up quotes in a reply. I can’t recall off hand as it’s been a long time since I last posted here.

12 minutes ago, Strange said:

For example:

https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_velocity_time_dilation

and:

https://en.wikipedia.org/wiki/Length_contraction#Derivation

As you can't remember the quotation or the source, I think it is more likely you have misremembered it than that the mathematics of SR is wrong.

Never mind, I figured it out.

I need to grab a bite and run some errands but I’ll try to reply today.

Please don’t lock this thread until I get back.

 

Edited November 25, 2019 by TakenItSeriously

[TakenItSeriously]

1 hour ago, Janus said:

with Relativistic blue-shift, you visually a higher frequency arriving from the approaching source, but that does not mean you conclude that time is proceeding faster for the source.

I agree.

1 hour ago, Janus said:

With classical Doppler shift, you also would see a higher frequency arriving from the approaching source but you would not conclude that time runs faster for the source, ...

Again I agree. I wasn’t trying to assert that time must be running faster. I was only trying to assert that you can no longer link time dilation as the cause for the relativistic blue shift.

1 hour ago, Janus said:

once you factor out the decreasing distance effect, you would conclude that time runs at the same rate for the source as it does for the receiver.    With Relativistic Doppler effect, once you factor out the decreasing distance effect you are left with time dilation and events occurring slower at the source.

You mean classical distance effect? In that the distance is decreasing classically due to motion?

I wasn’t trying imply anything about that. I was trying to say that relativistic blue shift must be due to length contraction of the distance. i.e. from Alices point of view at the turn around, her distance to the Earth is 0.6*4 ly or 2.4 ly due to length contraction.

1 hour ago, Janus said:

With Relativistic Doppler effect, once you factor out the decreasing distance effect you are left with time dilation and events occurring slower at the source.

Ok, here is where it gets super tricky.and deviates from what most people assume is happening so please try to keep an open mind.

From Alices point of view, is time still dilated on the return leg when Alice is now approaching Bob?

Empirically, we can’t conclude this because both clocks now seem to be running faster so I’m saying that time is not progressing faster or slower.

I’m saying that length contraction is nothing more than time dilation except as seen from the other side.

Again, relativistic redshift is due to time dilation of the frequency.

Relativistic blueshift is due to length contraction of the wavelength.

Edit to add:

If this has got you thinking, there are more consequences to it that can resolve a whopping mystery, but you kind of need to accept this step first.

 

Edited November 25, 2019 by TakenItSeriously

[studiot]

1 hour ago, TakenItSeriously said:

If I’m not mistaken, I believe the direction of travel quote was from Einstein himself. I cant recall exactly my source for this belief however length contraction is always stated in terms of the direction of travel.

 

I think you will be (mis) remembering the part where Einstein showed that time dilation/ length contraction is zero at right angles to the direction of travel and increases to its full value as the direction vector rotates to become parallel to the direction of motion.

I think Janus has linked to some striking videos showing the results of this effect.

[TakenItSeriously]

27 minutes ago, studiot said:

 

I think you will be (mis) remembering the part where Einstein showed that time dilation/ length contraction is zero at right angles to the direction of travel and increases to its full value as the direction vector rotates to become parallel to the direction of motion.

I think Janus has linked to some striking videos showing the results of this effect.

I don’t see any links posted by Janus.

However, your reply has just saved me some time in replying back to Strange.

He had stated that relativistic effects were true in the horizontal and vertical access and I was going to argue that assumption was in error.

I honestly can’t say anything about what I can distinctly remember about SR at least in regards to directionality. I first learned about it in the early 70’s when I was a child and my memories about it are spread across the entire range of time until now.

Edit to add:

Scratch that. I can remember learning about SR in school years later.

The teacher had stated “length contraction in the direction of travel” and I always interpreted that as literally only in the direction of a moving ship.

I also recall asking him if he meant to say that the dimension of space in the direction of travel not just the length of physical objects. We disagreed on that point and I quietly conceded that he was wrong because it does no good to argue with your teacher in grade school.

Edited November 25, 2019 by TakenItSeriously

[Strange]

5 minutes ago, TakenItSeriously said:

I honestly can’t say anything about what I can distinctly remember about SR at least in regards to directionality. I first learned about it in the early 70’s when I was a child and my memories about it are spread across the entire range of time until now.

Then you should refresh your memory to clear up your misunderstandings.

7 minutes ago, TakenItSeriously said:

However, your reply has just saved me some time in replying back to Strange.

He had stated that relativistic effects were true in the horizontal and vertical access and I was going to argue that assumption was in error.

I hope that means you realise that what I said was correct.