Are relativistic effects directional?

[Eise]

41 minutes ago, TakenItSeriously said:

Your kidding right?

You do realize that when you take the square root of any number you get a positive and negative result right?

But first, this is physics, not mathematics. One must always check if both solutions make sense physically.

Second, the direction of the velocity has nothing to do with the choice of the positive or the negative result, as Strange already showed, because you must use v².

So third, what do you get if you take the negative value as possible outcome? Say you compare two sticks, one flying in the opposite direction of the other, with the same speed. Due to the length contraction, one stick has for you a length of -0.5L, the other +0.5L. Which one is longer? 😈

So what is the physical meaning of a negative length?

Edited November 27, 2019 by Eise

[TakenItSeriously]

6 minutes ago, Eise said:

But first, this is physics, not mathematics. One must always check if both solutions make sense physically.

Second, the direction of the velocity has nothing to do with the choice of the positive or the negative result, as Strange already showed, because you must use v².

So third, what do you get if you take the negative value as possible outcome? Say you compare two sticks, one flying in the opposite direction of the other, with the same speed. Due to the length contraction, one stick has for you a length of -0.5L, the other +0.5L. Which one is longer? 😈

So what is the physical meaning of a negative length?

The directionality I’m talking about in the title is the relative velocity as in moving closer vs moving away or as in relativistic red shift which I link to time dilation vs relativistic blue shift which I link to length contraction.

Strange claimed that the kind directionality I was positing wasn't consistent with the math.

I showed him why it was consistent.

He then accused me of lying and then brought up the signs for the Lorentz factor for some reason.

I told him that the Lorentz factor as applied to the TP doesn’t have a sign because its not a vector.

[uncool]

17 minutes ago, TakenItSeriously said:

I really don’t know. Ask Strange, he brought it up.

No, you did. You are the one who said "Besides that the Lorentz factor is not a vector." I'm asking you, who said it, how that statement is relevant.

[TakenItSeriously]

2 minutes ago, uncool said:

No, you did. You are the one who said "Besides that the Lorentz factor is not a vector." I'm asking you, who said it, how that statement is relevant.

This post and the next post is where strange brought it up.

I didn’t understand why.

[uncool]

I don't see the word "vector', which is the relevant part of the statement I am asking about, in those posts. You are the one who first used it in the context of whether the Lorentz factor is one.

I'll ask in a slightly different way: what point were you trying to make with the statement "Besides that the Lorentz factor is not a vector."?

Edited November 27, 2019 by uncool

[TakenItSeriously]

Because I guess he was associating the sign with directionality or something.

The Lorentz factor as used in the TP doesn’t require a sign because it’s not a vector.

[studiot]

17 minutes ago, TakenItSeriously said:

Because I guess he was associating the sign with directionality or something.

The Lorentz factor as used in the TP doesn’t require a sign because it’s not a vector.

Having a sign or not having a sign does not make something a vector, neither does it prevent something being one.

You yourself have already posted statements acknowledging this, unless you can convince me that a square root satisfies the 9 vector axioms.

1 hour ago, TakenItSeriously said:

You do realize that when you take the square root of any number you get a positive and negative result right?

 

 

[swansont]

11 hours ago, TakenItSeriously said:

Ok, you’re right. That was a bad example.

Let me try to explain it another way but first allow me to outline what I think we do and don’t agree on so we can get on the same page. Some of this may be trivial to you but I’m just trying to cover all the relevant bases.

1. Light waves exist in space between source and observer as opposed to the Newtonian view where the SOL is instantaneous.
2. The speed of light is constant to all observers but the frequency of light is frame dependent according to the relativistic doppler effect.
3. If you agree with Janus, the causality of the relativistic component of relativistic redshift can be explained by time dilation.
4. So far we don’t agree on the causality of the relativistic component of relativistic blueshift.
5. Acceleration has been largely refuted by the physics community as the reason for the time deviation experienced by the twins.
6. You think that both length contraction and time dilation are true in moving frames regardless of whether the light source is moving towards an observer or away from an observer.
7. I think that time dilation is only true in frames where the light source is moving away and length contraction is only true in frames that are moving towards an observer.

Would you agree with the list above?

Please correct anything that’s wrong or feel free to add anything else you feel is pertinent.

#5 — without an acceleration, there is no deviation. It's not the source of time dilation, but it is the reason for the asymmetry in the effects.

#6 is correct, and verified, making #7 wrong (not the part about it being what you think, but the physics). Take the Hafele-Keating experiment. Time dilation depended on movement of East vs West, which boils down to faster or slower as compared to an inertial frame. Not moving toward or moving away, as they spent half of their time doing each, with respect to the clocks on the ground.  

[TakenItSeriously]

5 minutes ago, studiot said:

Having a sign or not having a sign does not make something a vector, neither does it prevent something being one.

You yourself have already posted statements acknowledging this, unless you can convince me that a square root satisfies the 9 vector axioms.

 

 

I agree and I’m not trying to say that it does.

Strange was the one who was trying to assign meaning to the sign of the Lorentz factor.

I only tried to tell him it doesn’t apply that way.

2 minutes ago, swansont said:

#5 — without an acceleration, there is no deviation. It's not the source of time dilation, but it is the reason for the asymmetry in the effects.

#6 is correct, and verified, making #7 wrong (not the part about it being what you think, but the physics). Take the Hafele-Keating experiment. Time dilation depended on movement of East vs West, which boils down to faster or slower as compared to an inertial frame. Not moving toward or moving away, as they spent half of their time doing each, with respect to the clocks on the ground.  

Thanks.

I’m going to have to get some sleep now.

I’ll get back to this later.

[swansont]

1 hour ago, TakenItSeriously said:

Your kidding right?

You do realize that when you take the square root of any number you get a positive and negative result right?

e.g. √4 = +2 & -2

Besides that the Lorentz factor is not a vector. It doesn't even have units.

You are free to come up with examples of the application of the negative root in this kind of problem.

You realize the fact that it's not a vector and uses scalars works against your position, right?

3 hours ago, TakenItSeriously said:

Not at all.

From Alices point of view length contraction is calculated for the distance to Alices destination that she is moving towards.

From Bob’s point of view her time is dilated as she moves away from him.

OK, now do the problem where Alice is starting at the distant star and moving toward Bob. Her length is still contracted the same amount and her speed is the same. How can her time not be dilated the same?

[TakenItSeriously]

3 minutes ago, swansont said:

You realize the fact that it's not a vector and uses scalars works against your position, right?

The directionality I refer to is the relative type as in moving away from the observer vs moving towards the observer.

In the problem

from Alices point of view, you calculate length contraction for the distance Alice has to travel (in the direction of motion.)

from Bobs point of view he knows the distance is 8 ly but he could calculate time dilation of a receding ship.

 

[Strange]

1 hour ago, TakenItSeriously said:

Strange claimed that the kind directionality I was positing wasn't consistent with the math.

It isn't.

1 hour ago, TakenItSeriously said:

I showed him why it was consistent.

If that is what you think then you don't even understand the simplest mathematics. 

 

1 hour ago, TakenItSeriously said:

I didn’t understand why.

That is a sad confession.

1 hour ago, TakenItSeriously said:

Because I guess he was associating the sign with directionality or something.

Velocity is a vector.

Therefore it has a sign.

The sign indicates the direction.

Velocity with a negative sign is in the opposite direction to velocity with a positive sign.

If you don't even understand basic concepts like this, it is not surprising you are so confused.

1 hour ago, TakenItSeriously said:

The Lorentz factor as used in the TP doesn’t require a sign because it’s not a vector.

Exactly. The Lorentz factor is scalar (not a vector). It is not dependent on the direction of the velocity.

Therefore the Lorentz factor (and therefore the time dilation and length contraction) is identical for something moving towards or away from you.

[Eise]

1 hour ago, TakenItSeriously said:

The directionality I’m talking about in the title is the relative velocity as in moving closer vs moving away or as in relativistic red shift which I link to time dilation vs relativistic blue shift which I link to length contraction.

And I was reacting at:

2 hours ago, TakenItSeriously said:

You do realize that when you take the square root of any number you get a positive and negative result right?

So what does the negative square root physically mean?

Then you should realise that the Lorentz factor is dependent on v², where the Doppler effect is only in the first order dependent on v.

That means you must distinguish between Doppler effect and time dilation. So when I have a light source moving fast to me, 2 things happen:

• Due to its speed there is time dilation, so the frequency of the light source becomes less, i.e. we have a red shift due to its speed.
• Due to its direction to me, I have a blueshift

You must consider both to get the full picture.

You must distinguish between what Bob observes, and what he concludes. A blueshift does not mean that there is no time dilation. If Bob takes Alices blueshift in account, he concludes that her clock runs slower compared to his.

1 hour ago, TakenItSeriously said:

I showed him why it was consistent.

And Strange reacted:

3 hours ago, Strange said:

Now do the same for the velocity in the other direction:

β = v/c = -0.8

the Lorentz factor:

α = √(1-β²) = 0.6 (the same value)

So the effect on length contraction and time dilation is identical.

Do you see this is correct? In the example the Lorentz factor is 0.6 independent of the direction. However, the Doppler effect is dependent on the flight direction.

But then you said:

2 hours ago, TakenItSeriously said:

You do realize that when you take the square root of any number you get a positive and negative result right?

On which I reacted with my post. What would be the physical difference wen you use the positive solution, or the negative? Again, what is longer: a stick with length 0.5L or one with a length of -0.5L?

[iNow]

Is anyone here familiar with the concept of diminishing returns, because we’re obviously well beyond that point now with this thread. 

[studiot]

 

2 hours ago, Strange said:

Velocity is a vector.

Therefore it has a sign.

The sign indicates the direction.

Velocity with a negative sign is in the opposite direction to velocity with a positive sign.

If you don't even understand basic concepts like this, it is not surprising you are so confused.

Not all vectors have a sign, for example the position vector.

Strictly speaking the vector -v is a different vector than v, if both exist.

[Strange]

10 minutes ago, studiot said:

 

Not all vectors have a sign, for example the position vector.

Strictly speaking the vector -v is a different vector than v, if both exist.

I hope that given the level of understanding shown by the OP my informal use would be acceptable.

[Eise]

22 minutes ago, iNow said:

Is anyone here familiar with the concept of diminishing returns, because we’re obviously well beyond that point now with this thread. 

Well, TakenItSeriously is at least, well, serious. He argues with others, does not claim that we are all idiots, and does not refer to some conspiracy theory why physics hides the truth; and he keeps being polite. But he obviously has a blind spot in his understanding of relativity. I just chimed in in the hope that another formulation would help him to see his error. Others in this thread know relativity much better than I do. (For me, Janus' explanations are becoming legendary...)

If people get tired, they can just stop reacting and reading the thread. 

[iNow]

All good points, and to be clear my comment wasn’t directed at you. We’re just now approaching page 4 of the thread yet repeating all of the very same points made in the first replies on page 1... over and over and over again some more. There’s a level of obstinance and obtuseness being shown that I’m not personally patient with, but feel free to carry on repeating yourselves. 

Edited November 27, 2019 by iNow

[studiot]

16 minutes ago, Strange said:

I hope that given the level of understanding shown by the OP my informal use would be acceptable.

It is often better to use a term like 'sense' or 'polarity' or even just 'sign' for positive / negative rather than 'direction' in technical stuff.
Especially for those objects that have a built in use of a particular meaning of the word direction.

Edited November 27, 2019 by studiot

[Eise]

10 minutes ago, iNow said:

All good points, and to be clear my comment wasn’t directed at you.

I know. But I give TakenItSeriously the benefit of the doubt. In one posting he was even trying to clear up where the viewpoints of the different 'discutants' lie.

And as I said, you never know when somebody because of a certain formulation or explanation is seeing the light (redshifted or blueshifted...).

[iNow]

11 minutes ago, Eise said:

I know. But I give TakenItSeriously the benefit of the doubt. In one posting he was even trying to clear up where the viewpoints of the different 'discutants' lie.

And as I said, you never know when somebody because of a certain formulation or explanation is seeing the light (redshifted or blueshifted...).

I’d be much more amenable to your view were this the first time it’s happened with our OP. Here are just 2 other examples among a good many others:

https://www.scienceforums.net/topic/113056-is-there-any-reason-this-quantum-telegraph-couldn’t-work/

https://www.scienceforums.net/topic/112104-original-solution-to-the-“liars-paradox”/?tab=comments#comment-1027579

Kudos on the Doppler humor, though

 

[phyti]

The spacetime graphic plots light motion ct on the vertical scale, and object motion vt on the horizontal scale. The object position is plotted for successive clock events, producing a history of positions. The slope of a straight line thus represents vt/ct or constant speed, thus a speed profile.

In the graphic, relative to the U frame (x, ct), A moves at .3c and B moves at .6c. In Newtonian physics, using t=x/v, A (black) arrives at 3x at Ut=10, and B (green) arrives at 6x at Ut=10. In SR physics, a clock rate is slower the faster it moves in space relative to a ref. frame. U concludes the A-clock rate is .95 his local clock rate, and the B-clock rate is .80 his local clock rate. If the B speed profile reverses (magenta) at R, and B rejoins A at .6c, the example becomes a 'twin' scenario.

There is no acceleration at R, since the change involves a zero time interval. The outbound and inbound segments can also be replaced with two profiles crossing at R.

The speed profile of B can vary anywhere within the blue profile for light. The out and back speeds are only equal in this case for simplification.

The graphic demonstrates that any speed profile that departs from that of A, loses time relative to A. If the graphic is rotated 180 deg, by symmetry, the same method will produce the same results for speeds in the opposite direction.

Additionally, even though the Lorentz/gamma factor is a function of (v/c) squared, speed as shown is a ratio or scalar, thus a negative speed is not a real world solution. You can’t move slower than zero. There is also an inconsistency with ‘velocity’ defined as ‘speed’ in the 1900’s, with the additional mention of direction, and today’s definition of ‘velocity’ as a two-component concept.

Doppler shift is an altered perception of a constant frequency, caused by the observer’s motion relative to the source. It does not indicate the rate of a moving clock. An observer’s motion cannot alter the rate of a distant clock, but it can alter his perception.

[TakenItSeriously]

10 hours ago, swansont said:

#5 — without an acceleration, there is no deviation. It's not the source of time dilation, but it is the reason for the asymmetry in the effects.

#6 is correct, and verified, making #7 wrong (not the part about it being what you think, but the physics). Take the Hafele-Keating experiment. Time dilation depended on movement of East vs West, which boils down to faster or slower as compared to an inertial frame. Not moving toward or moving away, as they spent half of their time doing each, with respect to the clocks on the ground.  

Damn, I lost my entire last post due to an outage. Hopefully I’m back now.

#5 Regarding acceleration. I mostly agree especially with how it plays no role in explaining the time deviation experienced by the twins. Perhaps not as much as with the asymmetry of the other effects.

Acceleration, while once accepted as the underlying cause, has since been refuted because of a modified TP thought experiment which removed all acceleration from the problem and you still end up with the same results.

It adds a complex asymmetric effect to be sure but it’s irrelevant to the simple form of the problem when using only velocity.

You can look it up here: https://en.wikipedia.org/wiki/Twin_paradox?wprov=sfti1

Under Twin Paradox subtitle: the Role of Acceleration.

A synopses of the modified version includes three observers

1. Bob at rest on Earth.
2. Alice drifting past the Earth at 80%c on her way to the star 8 ly away.
3. Carole drifting in the opposite direction at 80%c passes the star at the same time Alice passes it.

Carole collects Alices information such as travel time, travel distance from the Earth, observations on Bobs time, etc. She then proceeds to Earth and passes all of Alices information as well as her own to Bob and the time experienced by both travelers only adds up to 60% of the time experienced by Bob.

#6 I recall the Hafle-Keating experiment using jet airliners and atomic clocks and I agree that it does seem to represent a bit of a conundrum. However, I would question whether the time dilation measured was due to gravity or velocity. For example, I’ve been told that the time dilation calibrated for in GPS satellites is almost entirely due to gravity. I know, different elevations and speeds, but I just get the feeling that gravity still dominated time dilation in that experiment but IDK for sure.

In any case, I’ve tried to consider how to adapt orbital information into the TP and it’s just beyond me so I let it drop and left the question to smarter minds to ponder than my own.

Now we already agree that time dilation is the cause of the relativistic component of relativistic red shift.

So how I would explain the cause behind the relativistic blue shift effect:

Using the original example, Alice has just turned around and is headed for Earth.

From Bob’s PoV:

Alice is racing her own light traveling at 100%c while she is moving at 80%c. Another words it takes the light 8 years to reach Earth while it takes her ship 10 years. Therefore all of her transmissions on the return leg must be compressed into only two years. So this blue shift effect can all be explained by simple lag-time for the light to travel such a distance just like communications in our own solar system.

No time dilation involved.

However there is still the difference between relativistic blue shift and normal blue shift so what explains this difference.

Well, Bob would expect Alices return leg to take 10 years which is squeezed into 2 years. However, after he meets Alice and counts the pings, he sees that there was only 4.8 years of pings compressed into those 2 years.

As I mentioned before, the 60% of the time she experienced on her journey home is due to traveling only 60% of the distance due to length contraction.

To look at it another way, we agree that:

1. light waves from Alices ship exist in the space between Alice and the Earth.
2. We agree that information is conserved and no waves (or pings) are either inserted or deleted.
3. We agree that from Alices PoV the distance between the Star and Earth is length contracted to only 4.8 ly

So what do you think happens to those light waves in length contracted space?

The waves themselves must also be contracted...well at least those waves that are received from their sibling.

 

You see the waves that are emanating from Alice’s ship are all part of the ships inertial reference frame.

 

The waves that are emanating from Bob are all part of the Earth’s inertial reference frame.

 

So from Bob’s PoV, the waves transmitted from Alice are length contracted.

 

From Alices PoV, the waves transmitted from Bob are length contracted.

 

Note that the waves coming from their own transponders are always pinging at 1 sec per sec. Another words the waves transmitted from their own transponders are all in each twins own respective inertial reference frame regardless of where they are in space.

QED

 

Edited November 27, 2019 by TakenItSeriously

[swansont]

19 minutes ago, TakenItSeriously said:

 

• #6 I recall the Hafle-Keating experiment using jet airliners and atomic clocks and I agree that it does seem to represent a bit of a conundrum. However, I would question whether the time dilation measured was due to gravity or velocity.

You can quantify it. You can’t get to the right answer without properly accounting for each.

Quote

• For example, I’ve been told that the time dilation calibrated for in GPS satellites is almost entirely due to gravity. I know, different elevations and speeds, but I just get the feeling that gravity still dominated time dilation in that experiment but IDK for sure.

Yes. 45 microseconds a day vs 7. But if the 7 is ignored, that’s more than 2 km of positioning error building up each day. I think we’d notice 

[Janus]

21 hours ago, TakenItSeriously said:

Acceleration has been largely refuted by the physics community as the reason for the time deviation experienced by the twins.

No. You are over-generalizing a particular conclusion about the role of acceleration beyond its meaning. 

The conclusion is based on the "clock postulate".  Basically it states that local acceleration has no effect on the operation of a clock.  In other words, if you take a clock and put it in a high speed centrifuge and spin it up, the fact that the clock is experiencing a high value of acceleration has no additional effect on the rate of the clock ticking as measured from the lab frame. The clock will tick slow, but only by an amount due to its velocity relative to the lab frame.

This is not the same as saying that acceleration plays no role in the resolution of the Twin paradox.  The clock postulate only deals with how an inertial frame measures the accelerating clock, and does not deal with what would be measured from the accelerating frame itself.   

So for example, assume we have clock sitting at the center of the centrifuge in the lab frame. In addition to the clock spinning in the centrifuge, and the central clock, we have a third clock and observer traveling in an inertial frame at the same speed as the centrifuge clock and at a tangent to it such that its path and the centrifuge clock just touch at one point, so that if the two clocks were at that point at the same moment, they would have identical instantaneous velocities.  The difference being that the centrifuge clock has an acceleration toward the center clock,a and the third clock doesn't.  

If we compare what these two clock conclude as to what is happening two the center clock at that moment, they would come to different conclusions. the inertially moving clock would say that the central clock is running slow, while the centrifuge clock, which is under acceleration, would say that the central clock runs fast.

If a physicist says that acceleration is not the reason for the time difference they mean that in a specific way, and you are trying to infer a much broader meaning beyond that which they meant.