What has the speed of light got to do with time travel?

[Fredrik]

Anyway, just because one were to propagate information about an event FTL, that doesn't mean one is violating causality, because the propagation of that event would still be happening after the fact of that event.

See my post in this thread.

But one thing that's always bothered me is the question of why the speed of light is always the same to every observer, regardless of reference frame velocity.
How is it possible for light to exhibit this characteristic?
What is the underlying reason for it?

First of all, you shouldn't think of it as a property of light. The existence of inertial frames and the fact that a certain type of straight line looks the same in all of them is a property of spacetime, not a property of light.

Light does however have the property that it moves at the speed that's associated with the "straight lines" mentioned above. It has to, because photons are massless particles. This is one of the things you find when you combine quantum mechanics with special relativity.

And of course, why does the speed of light have the particular value it has? (ie. 3x10^8 m/s)

No one knows.

 

[cybersurf88]

Ok, I take it you'll be first in line to volunteer for the quantum transporter?


Two reasons: 1) signaling is not travel; 2) MWI avoids causality paradoxes.

How do you view Dr. Gisin's entangled twin photon experiment in FTL signaling and its
implications on practical informational systems. Is the instantaneous twin aberrational
behavior of light photons "merely" explained by random behavior and unpredictability
states and conditions within quantum mechanics? Can signaling become informational?
...

nb. Thank you JesseM for your extraordinarily insightful understanding and explanation.

SEE:
"Entangled particles are identical entities that share common origins and properties, and remain in instantaneous touch with each other, no matter how wide the gap between them..."

"... "collapse of the wave function." ...is that if just one particle in an entangled pair is measured, the wave function of both particles collapses into a definite state that is the same for both partners, even separated by great distances. "
http://www.cebaf.gov/news/internet/1997/spooky.html Jefferson Lab

 

[JesseM]

How do you view Dr. Gisin's entangled twin photon experiment in FTL signaling and its
implications on practical informational systems. Is the instantaneous twin aberrational
behavior of light photons "merely" explained by random behavior and unpredictability
states and conditions within quantum mechanics? Can signaling become informational?

Gisin's experiment does not involve "signaling", only the correlations characteristic of entanglement, but there is no way to use these correlations to gain any information on what measurement was performed on the other distant particle before a classical signal about the measurement has had time to reach you. It has apparently been proven that according to orthodox quantum theory, there is absolutely no way to use entanglement to send FTL signals--there is a theorem by Phillippe Eberhard to this effect, see here. Depending on your choice of interpretation of QM, you may believe there are some "hidden" FTL effects needed to explain the correlations seen in entanglement, but as peter0302 said, advocates of the many-worlds interpretation do often argue that the MWI can explain these correlations without the need for even hidden FTL effects.

 

[cybersurf88]

Thank you. Apparently my question was not precise. I am aware that instantaneous
identical behavior of entangled light photons over long distances did not evidence
FTL informational transmission between the twin photons or any evidence of signaling between the entangled photons.

However, I will rephrase the question as:
Whether the behavioral characteristics of entangled LP can or will present itself as a paradigm for FTL informational systems?

Although the concept of causality in physics is distinct from philosophical causality or legal causality in tort (negligence) cases, I draw from analytic (linguistic-Wittgenstein) philosophy to define causation as being the direct or proximate cause (substantially contributing factor) which resulted in a particular action. As you noted, information can theoretically arrive faster than it is sent. Could instantaneous identical behavioral changes by entangled photons infer that each of the twin photons receive programming instructions independently from another common FTL broadcasting source?

Would the common broadcasting source be a direct or proximate cause of the twin
LP changes over long distances.

This issue is distinct from the proven hypothesis that LP do not communicate between each other.

Do the equations and explanations of long distance - instantaneous twin LP changes
limit our understanding to "aberrant, unexplainable" conditions that fall within quantum physics and quantum mechanics?

What equational inquiries would rule out direct or proximate causation of twin LP
changes by a separate common broadcasting source?

If empirical evidence cannot rule out a common FTL broadcasting source, can
a theory of a single broadcasting source or "collective- but separate broadcasting
sources" be constructed that proves a necessity for the existence of a "broadcasting source for entangled LP?

Instantaneous LP character changes over long distances without an "instructional source" is illogical. It's "spooky quantum mechanics."

Keep in mind Dale's comment to Flash, "...Flash, you'll be traveling so fast that you'll arrive before leaving..."

Anyway, you guys are a hell-a-va lot smarter than me in this area.
So...can I respectfully ask if anyone in this forum is affiliated with university research or teaching. What are the educational backgrounds of the contributors in this forum? The quality and calibre of the discussions is impressive.

I will give my background to anyone who is interested.
Be good, take care all.

 

[Max™]

Light is measured to have a constant velocity even when you're moving rapidly because of the time dilation you incur as you move faster.If you move fast enough that your subjective second corresponds to 1.5 seconds for a beam of light, then you would measure a beam of light crossing 1.5x light-seconds

You yourself would have crossed .5 light-seconds.

So you "see" a second, measure the motion of the light for "a second", move half a light-second, and the beam of light moves 1.5 light seconds.That is why the speed of light is always measured to be constant, and why it is invoked in SR. Not as a statement about the speed of light at all.

Rather as a statement about how motion through space affects motion through time.

 

[JesseM]

Light is measured to have a constant velocity even when you're moving rapidly because of the time dilation you incur as you move faster.

There is no objective truth about who is "moving rapidly" though. If you and I are moving at 0.8c relative to one another, then in my frame I am at rest and you are moving at 0.8c, and your clock is slowed down by a factor of 0.6 relative to mine. Likewise, in your frame you are at rest and I am moving at 0.8c, and my clock is slowed down by a factor of 0.6 relative to yours. There's no real fact of the matter of which of us is "really" moving faster or which of our clocks is "really" running slower.

Also, the fact that each observer measures the speed of light to be c can't be explained solely by time dilation, you also need to take into account length contraction since speed is defined in terms of distance/time, and you need to take into account the relativity of simultaneity (the fact that each observer sees the other one's clocks being out-of-sync). See my post #6 on this thread for a numerical example of how all these factors come together to ensure that both observers measure a photon to move at c.

If you move fast enough that your subjective second corresponds to 1.5 seconds for a beam of light

What do you mean "for a beam of light"? The light does not have its own frame.

then you would measure a beam of light crossing 1.5x light-seconds

If in your frame a light beam travels for 1.5 seconds, then in your frame it will have moved 1.5 light-seconds--is that what you mean?

You yourself would have crossed .5 light-seconds.

0.5 light-seconds in whose frame? In the frame of the observer who sees your clock take 1.5 seconds to tick forward one second? If so, your numbers are incorrect, in order to have gamma = 1.5 in my frame, your velocity must be approximately 0.745346c in my frame, so in 1.5 seconds I'd see you travel 1.5*0.745346 = 1.11803 light-seconds.

 

[Max™]

Why does the beam of light not have it's own frame?

What would an event look like for a beam of light, if it was an observer?

They're weird questions which aren't normally approached.Yes I did neglect the length contraction for simplicity, it all applies and should be calculated to be accurate, but the point is that the measured speed of light being constant is a statement about the way we interact with space-time, not the speed of light itself.

Light interacts with space-time in a different manner, for it has no rest mass.Naturally this will all be observed differently for an observer in a different frame of motion.

I apologize because I too naturally include GR assumptions about acceleration and reference frames, but to be fair, SR is not truly complete without GR.

 

[JesseM]

Why does the beam of light not have it's own frame?

What would an event look like for a beam of light, if it was an observer?

This is a question which has been discussed on many previous threads here. Here was my brief explanation in one older thread:

Inertial frames are supposed to be defined by networks of rulers and synchronized clocks at rest in that frame, but it's impossible for rulers and clocks to be accelerated to the speed of light, and even if you consider the limit as they approach the speed of light, the rulers' length would approach zero due to Lorentz contraction and the clocks would approach being completely frozen due to time dilation, so you couldn't construct a sensible coordinate system out of them. One more reason that light can't have its own inertial rest frame is that one of the fundamental postulates of relativity is that the laws of physics should be the same in every inertial frame, but light can never be at rest in the rest frame of any object moving slower than light, so giving light its own rest frame would violate this postulate.

For more on the subject of light not having its own frame, you might look at this thread or this one.

Yes I did neglect the length contraction for simplicity, it all applies and should be calculated to be accurate, but the point is that the measured speed of light being constant is a statement about the way we interact with space-time, not the speed of light itself.

What do you mean by "the speed of light itself"? Do you think objects have a true speed which is separate from the distance/time measured by various sets of rulers and clocks?

I apologize because I too naturally include GR assumptions about acceleration and reference frames, but to be fair, SR is not truly complete without GR.

SR is complete as long as you are dealing with a situation where spacetime is not curved (just assume the mass of all the particles is negligible). You can certainly deal with acceleration in SR, see here.

 

[cybersurf88]

...ask if anyone in this forum is affiliated with university research or teaching. What are the educational backgrounds of the contributors in this forum?

Can anyone link me to abstracts on FTL communication...?

 

[Max™]

For a photon, a point in space directly corresponds to a point in time.

Photons move through time in a way which is equivalent to motion through space.

Yesterday for a photon is "over there", tomorrow is "that way", now is "right here".

We (bodies with rest mass) move through time at a much reduced rate. Having a rest mass, or sitting still in an inertial frame, can be considered motion at a sub-light velocity from another frame.

If you're moving through space at a sub-light velocity, you are falling behind the time marked out by a photon. You observe this as time dilation.If a photon passes you at "now", and you take off at, say, twice the speed of light in the same direction. When the photon crosses a light minute (1 minute later from the "now" it passed you), you're 1 light minute ahead of it.

You then turn around and go past the point where the photon crossed you, but you are "ahead" of it. The photon is actually further back along it's path than it was when it first passed you.

You crossed that "now" before the photon did, because you went back in time along a closed timelike curve.These ideas seem weird until you consider what the universe looks like to a photon.

That is similar to what Godel was doing when he constructed his Godel Universe.

 

[JesseM]

For a photon, a point in space directly corresponds to a point in time.

Photons move through time in a way which is equivalent to motion through space.

Yesterday for a photon is "over there", tomorrow is "that way", now is "right here".

What coordinate system are you using to justify these statements? And what is the physical basis of such a coordinate system? Keep in mind that for inertial coordinate systems for observers moving slower than light, all coordinates are intended to reflect the measurements on a hypothetical set of rulers and synchronized clocks which are at rest relative to that observer--for example, if I see an explosion happen in space right next to the 8 light-second mark on the ruler at rest relative to me that represents my x-axis, and the clock sitting at the 8 light-second mark which is synchronized with my own (according to the synchronization convention) reads 5 seconds at the moment the explosion happens, then I assign that explosion coordinates x=8 light-seconds, t=5 seconds. Do you have any kind of analogous way to ground the coordinate system of a light ray in terms of physical measurements?

 

[Max™]

What coordinate system are you using to justify these statements? And what is the physical basis of such a coordinate system? Keep in mind that for inertial coordinate systems for observers moving slower than light, all coordinates are intended to reflect the measurements on a hypothetical set of rulers and synchronized clocks which are at rest relative to that observer--for example, if I see an explosion happen in space right next to the 8 light-second mark on the ruler at rest relative to me that represents my x-axis, and the clock sitting at the 8 light-second mark which is synchronized with my own (according to the synchronization convention) reads 5 seconds at the moment the explosion happens, then I assign that explosion coordinates x=8 light-seconds, t=5 seconds. Do you have any kind of analogous way to ground the coordinate system of a light ray in terms of physical measurements?

Set x = t?

If an event happens 8 light seconds along x from a beam of light's reference frame, then it happened 8 seconds away in t.Time = Space for a beam of light, any change in Time is equal to the distance covered in Space.

Weird to think about, huh.To put it another way, a beam of light has no rest frame, as it has no rest mass.

 

[cybersurf88]

A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring;
There shallow draughts intoxicate the brain,
And drinking largely sobers us again. -- Alexander Pope
----------------------------------------------------
Happy to see that someone else enjoys the "musings"
of our greatest metaphysical poet...and is sharp enough
to quote Pope's admonishment of "not drinking deep enough
into the spring of knowledge..." beyond the common day
practice of mistakenly saying, "...a little knowledge is a dangerous thing."
...NOW, back to quantum physics / mechanics.

In '69 I read Wheeler & Planck's Theories of Black Holes in Space.
Singularity has come a long way from '67 when Planck coined the phrase
"black hole." Will anyone venture a guess about what we can expect from
the LHC? Will Hawking again be disproved as a pie in the sky philosopher,
like his "information lost theory?" Any bets on the search for HIGGS?

I'll bet dollars to donuts that the HIGGS will be proven [ ] or non-existent [ ].
(I'll check off a box after I give this more thought)
cybersurf88

 

[cybersurf88]

FUTURE HEADLINES

LHC proves HIGGS [ ]
LHC proves HIGGS continues to "evaporate" detection [ ]

 

[cybersurf88]

Dr Brian Cox of the University of Manchester adds: "The energies of billions of cosmic rays that have been hitting the Earth's atmosphere for five billion years far exceed those we will create at the LHC, so by this logic time travellers should be here already. If these wormholes appear I will personally eat the hat I was given for my first birthday before I received it."
Statement made in response to assertions that the LHC will become the beginning point
for future time travellers to return to. (Russian scientists)
-----------------------
So...
What events occur at the horizon of a microcosmic black hole?
Microcosmic black holes are theoretically created around us everyday
according to some quantum physicists. Are light and time drawn into
the gravitational center of a microcosmic black hole as happens within
nebulas? Some LHC participants anticipate a potential for the creation
of time distortions / wormholes by LHC microcosmic black holes.
What if information passes consistent with the Hawking paradox of parallel universes?
Would information passing into a PU preclude time travel?
How about creating a clean equation of non-linear parallel universes.
For example, I propose / hypothesize that our entire universe is merely a subatomic particle lying like a grain of sand in a sand dune of universes. (c)
What if our entire cosmic existence is a mere speck of dust on some cosmic policman's
badge? Although we are free willed and our future is non-determinist, what if
time and matter have already completed our full cycle and we are existent only
as defined by a specific framed constant of time and space, within many frames and constants of time and space, where some constants are prologue and others are completed cycles as our epilogue.
Singularity presumes the existence of a subatomic condition for the big bang.
Is the presumptive condition before the big bang a necessary corrallary of the
existence of "sand dune universes?"
Could the evaporative HIGGS evidence time and place distortion or travel?
Is a single theory of creation unachievable because it necessarily must include
a rare interaction of multiple universes of which the discipline has failed to prove
mathematicallly or objectively verify?

 

[cybersurf88]

I am aware that multiple dimensions of time is outside of conventional and proven
theories. The closest work on multiple dimensions of time is that of the Bars theory of two dimensions of time. SEE: http://physics1.usc.edu/~bars/research.html#2T

 

[cybersurf88]

Itzhak Bars, "While taking exactly two timelike dimensions produces a coherent theory, investigations of alternatives with more than two times have been done (including alternatives to Sp(2,R)). So far such possibilities are ruled out because of problems with ghosts and unitarity, and this seems to confirm the special status of 2T-physics."
------------------------------
No responses to this site...? I think it's time for me to move to another site.
Thank you Jesse M for your assistance.

 

[Charlie G]

Think of it like this, we have one guy whos got his new car that travels at 99% the speed of light, his friend wants him to race a beam of light with his new car. He stands next the car with a laser and when he says go the driver zooms off at the smae time the other guy turns on the laser. The laser guy sees the driver trailing along the beam of light, right behind it almost. However the driver returns claiming that no matter what he did the light shot past his car at 100% the speed of light. How is this possible? Time must slow down for the observer in the car.