# Do you think Relativity theory can explain all the paradoxes?

ghwellsjr
Gold Member
From this long debate what i understood is only one thing.
The proton hits the earth AFTER THE DEATH OF ROBERT from earths rest frame. That is sure & the proton ages only a few days
But when you are considering the rest frame of proton, you are varying time of the earth inorder to solve the paradox.

How is that possible?
If the proton is at rest in it's frame and rest of the universe is moving, then how come the time on earth suddenly jumps into 2018 from 2014?
I need to know what kind of math/relativistic principle is used here?
As has been pointed out, there is no standard way to define how the proton can be "at rest in its frame" but my favorite way is to use the radar method which works identically to the standard Inertial Reference Frames (IRFs) and yet also works seamlessly with non inertial reference frames of the type you presented.

You mentioned in your OP that:
Both the planets are synchronised in time by sending light pulses so that they can keep 2013 on both planets.
It's important that both planets send signals in order for the proton to determine the correct synchronization. So let's see how this works. Let's assume that Planet X and the proton at some point in time don't know the time on earth. They send a message at the speed of light to the earth requesting them to immediately send a message back with the current time on the earth. The proton (and Planet X) start their stopwatch when the message was sent to earth and stop their stopwatch when they receive the response from earth. Then they take half of the measured time and assume that earth sent the response at that time and they go back and re-assign that time to their own time at the half-way point. They also assume that earth was that same number of light-years away at the time it sent the response. Here is a spacetime diagram to show how they do this using the same scenario (0.97c and 4 ly) as I did before:

Note that the proton sent its request when its stopwatch read 0 and it receives the response from earth when its stopwatch read 8 years so it assumes that earth received its message and sent its response when its stopwatch was at 4 years and since the message from earth said they were at the year 2008, the proton assigns 2008 to the point where its stopwatch was at 4 years. The proton also assigns all the other years before and after accordingly.

In the meantime, the proton has sent another message one year after the first one and similarly confirms that earth's year 2009 matches its year 2009 (since it's halfway between 2005 and 2013). Likewise, the proton concludes that the earth remains 4 light-years away:

The proton continues to send a new request to the earth every year and continues to keep track of sent/received times so that it can construct a non IRF diagram:

Here is a complete list of the information the proton has gathered:

Code:
Message   Response   Calculated   Calculated    Earth's
2004     2012         2008          4           2008
2005     2013         2009          4           2009
2006     2014         2010          4           2010
2007     2014.123     2010.56       3.56        2011
2008     2014.247     2011.12       3.12        2012
2009     2014.370     2011.68       2.68        2013
2010     2014.493     2012.25       2.25        2014
2011     2014.616     2012.81       1.81        2015
2012     2014.740     2013.37       1.37        2016
2013     2014.863     2013.93       0.93        2017
2014     2014.986     2014.49       0.49        2018
Now it's a simple matter for the proton to make a spacetime diagram for its non-inertial reference frame. Note that I'm drawing the position of the earth to the left of the proton just to maintain similarity to previous diagrams:

And just as a sanity check, we can show how all the signals that the proton sent and the responses that the earth sent are just as valid in this non-inertial frame as they are in the inertial frame:

As you can see, there's no jumping of any times (clocks) and no times (clocks) going backwards. The math is simple, averaging two measurements and dividing the difference by two. The relativistic principle is that the proton assumes that the signals that it sends to the earth take the same amount of time as the responses the earth sends back. Very simple, isn't it?

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stevendaryl
Staff Emeritus
Since I threw out "option 3" as my best understanding of your (and some others) approach, I wouldn't try to redefine coordinate charts. I would say using option 3 means you change coordinate charts every time your motion changes. At any change of motion, you translate your prior chart to a new chart. Personally, I don't see any value to this approach, nor do I think it provides any insight at all about "reality", but (so far) I don't see any reason that it is not a logically consistent approach that can be use to make correct predictions.
I think that students are misled in introductions to Special Relativity with all the talk about observers. It's not really correct that things (like simultaneity, velocity, length, etc.) are relative to an observer; they are relative to a coordinate system. The connection with observers is just that if the observer is inertial, then there is a natural, most convenient, coordinate system for that observer. If the observer is non-inertial, then the notion of things being "relative to the observer" has almost no value at all.

With Galilean relativity, it makes sense to ask: "How old is Jill when Jack is 20?" Students learn that simultaneity is relative, so the question doesn't have a unique answer. They know that the answer can be different depending on whose point of view you're considering. But if an observer is noninertial, then the question "How old is Jill when Jack is 20, according to that observer?" still doesn't have a unique answer.

You can stipulate that "Jill's age, relative to Jack" means "Jill's age, relative to an inertial coordinate system in which Jack is momentarily at rest". This notion of relative age is highly artificial and has really weird properties. If Jill is far away from Jack, then Jill can age rapidly in a short amount of time, or can even "youthen", depending on Jack's acceleration.

1 person
ghwellsjr
Gold Member
I'll give you another thought experiment, Instead of proton, use Jack and instead of earth use Jill, both are 20 years old and are 4LY away. If Jack moves towards Jill (Please remove Acceleration), how old will be Jack when he reaches Jill?
Okay, just answer what will be their age when they both meet together?

When it is 2014 on planet x (on earth too) they eject the proton towards the earth.
Just imagine that this proton has an 'inbuilt clock' in it (just imagine).
As soon as the proton leaves the accelerator, a stopwatch which which is attached to it activates.
Scientists on earth expect the proton reaching the earth on 2018 + some months.
Unfortunately a scientist (Robert) on earth dies in 2017 and proton reaches the earth on 2018.
The proton will have only aged an year or so.
So let's substitute Jack for the proton and put Jill on the earth:

When it is 2014 on planet x (and on earth where Jill is at the age of 20) they eject Jack (who is also 20) towards the earth.
Just imagine that Jack has a clock with him (just imagine).
As soon as Jack leaves the accelerator, a stopwatch which is attached to him activates.
Scientists on earth expect Jack reaching the earth on 2018 + some months when Jill will be 24 + some months.
Unfortunately a scientist (Robert) on earth dies in 2017 and Jack reaches the earth on 2018.
Jack will have only aged a year or so, so he will be 21.

I'm curious: why did you ask a question that you already provided all the information needed to answer it yourself?

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Which is why option 3 is not possible as a valid non-inertial chart.

Your position is not in keeping with mainstream scientific practice. See for example chapter 2 here:
http://arxiv.org/abs/gr-qc/9712019

If you take your approach then you lose much of the basic mathematical structure that you need. You can no longer do coordinate transformations, find neighborhoods of coordinates, differentiate wrt the coordinates, etc. That is why it is a bad idea and is expressly contrary to the mainstream approach. You gain no benefit from it, and the price is way too steep, particularly since almost all physics requires differentiation.
Firstly, happy Turkey Day to all.

On another matter, let's say one uses radar time to determine the velocity of the target, using τ1 = ½( τ0+ τ2). Would not the non-inertial POV (of relative relativistic rate) often record superluminal motions?

Thank You,
GrayGhost

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WannabeNewton
On another matter, let's say one uses radar time to determine the velocity of the target, using τ1 = ½( τ0+ τ2). Would not the non-inertial POV (of relative relativistic rate) often record superluminal motions?
It is possible for the coordinate speed of light to deviate from ##c## in a non-inertial frame and it is possible for the coordinate speed of time-like particles to reach ##c## but these quantities do not correspond to physical observables! The speed of light as measured at a given event using the rulers and clock of a local Lorentz frame comoving with the non-inertial frame at said event will always be ##c## and that of a time-like particle will always be less than ##c##.

Let an observer ##O## have 4-velocity ##\xi^{\mu}## at an event ##p## in space-time. A time-like particle with 4-velocity ##\eta^{\mu}## passes by at ##p## and ##O## makes a measurement of it's speed. Well speed is change in spatial distance (according to ##O##) divided by change in time (according to ##O##) so consider a future event ##q## infinitesimally close to ##p## that is on the worldline of this time-like particle. How do we measure the spatial distance between these two events? Well we project the vector pointing from ##p## to ##q## onto the local simultaneity slice of ##O## at ##p## and take its length. Similarly, to find the time between ##p## and ##q## we project this vector onto the time-axis of ##O## and take its length. The vector pointing from ##p## to ##q## is just ##\eta^{\mu}##.

Mathematically, projecting onto the local simultaneity slice of ##O## at ##p## just means projecting orthogonally relative to ##\xi^{\mu}## at ##p## which (from elementary linear algebra) is ##\eta^{\mu} + \xi^{\mu}\xi_{\nu}\eta^{\nu}##. Similarly, projecting onto the time-axis of ##O## just means projecting onto ##\xi^{\mu}## i.e. ##-(\xi_{\nu}\eta^{\nu})\xi^{\mu}##. The respective lengths are then ##[ (\xi_{\mu}\eta^{\mu})^2 -1]^{1/2}## and ##\xi_{\mu}\eta^{\mu}## so the speed of the time-like particle relative to ##O## is ##v = \frac{[(\xi_{\mu}\eta^{\mu})^2 -1]^{1/2}}{\xi_{\mu}\eta^{\mu}} < 1## in units where ##c = 1 ##. It can similarly be shown that for light, the change in spatial distance divided by change in time (all relative to ##O## as usual) is always ##c = 1##.

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Nugatory
Mentor
folks argued that SR was invalid and not mainstream because the euclidean metric did not relate 2 frames of relative motion, a new (Minkowski) metric did.
Which folks, and when?

Dale
Mentor
let's say one uses radar time to determine the velocity of the target, using τ1 = ½( τ0+ τ2). Would not the non-inertial POV (of relative relativistic rate) often record superluminal motions?
No, I don't think that it ever would. But as WBN pointed out the v<c limitation applies only to inertial coordinates anyway.

ghwellsjr
Gold Member
On another matter, let's say one uses radar time to determine the velocity of the target, using τ1 = ½( τ0+τ2). Would not the non-inertial POV (of relative relativistic rate) often record superluminal motions?
First off, I don't know how you can determine the velocity of a remote target by using just τ1 = ½(τ0+ τ2). You also need to use x1 = ½(τ2-τ0), using compatible units such as years and light-years. And of course, you need to make several measurements and repeat the calculations to track the position of the remote target as a function of the local time and from that, the velocity in the non-inertial frame can be calculated using the radar method.

For example, in post #51, I went into all the details about how the proton can construct its non-inertial rest frame using the radar method and it determines that the earth approaches it at a speed of 0.8c even though in the earth's rest frame, the proton is traveling at 0.97c.

You will also note that light continues to travel at c in the non-inertial rest frame just like in the IRF's (because we define it to do that). In fact, You can take the information contained in the proton's non-IRF and re-construct the earth's IRF.

So as far as I can tell, there are never any superluminal motions of massive objects and light always propagates at c when using the radar method because we are still using Einstein's second postulate.

Does this make sense to you?

ghwellsjr
Gold Member
I need to know what kind of math/relativistic principle is used here?
Did you understand my answer in post #51?

Very simple, isn't it?
Did it answer your question or does it not seem simple to you?

I hate to see questions go unanswered and unless you provide feedback, we'll never know how effective the answers were.

All,

It is not my practice to not respond to the posts of others. I have been told by mentor that my interpretation of option 3, which envisions events shifting in (space)time, is not mainstream relativity, and should not be discussed in this forum. The reason, is because only 1 coordinate chart may be used per POV, and events cannot relocate (even if by POV rotation alone, during frame transitioning). As such, I respect that, and will make no further responses on this matter in this thread or in this forum. Also just to be clear, I have never suggested that events could move in the all-inertial scenario, and I am not adept in GR admittedly. Thanx for your time and thoughts on the matter.

Thank You,
GrayGhost

1 person
This is what we gets from a protons reference frame, both predictions are according to relativity and both are real. But it's a paradox.
In the first event from earths rest frame the scientist Robert dies before seeing the proton and in the protons rest frame of reference The scientist is alive!
So how do relativity solve this paradox?
How can MS Diagram can solve this paradox?
I agree they can represent it on a diagram but it doesn't solve the paradox.
If it solves how can i visualize it, i mean i need a picture with definite result, a result that is agreeable for all observers
This is the same as twins paradox. You probably don't see the difference between proton's frame (non-inertial) and planets' frames (inertial).
The best (imo) explanation is here http://www.if.ufrgs.br/oei/santiago/fis02012/FirstCourseGR.pdf [Broken] on the page 25.

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