[nilak (OP)]

Is it possible to determine, mathematically, if a EM wave is travelling in one direction or another, only by knowing the values of electric an magnetic fields it produces at a moment of time ?
 It is a question of whether at certain polarization the wave looks the same as another in a different direction but different polarization, in my opinion.  That would mean finding the direction and speed of a photon without measuring succesive positions.

[Atomic-S]

The quantity (E x H)  [ H being an experession for the magnetic field strength] is called the Poynting vector, and its divergence  ∇•(E x H) equals the rate of change of electromagnetic energy density at the place evaluated. Thus the Poynting vector can be interpreted as an energy flux. Correspondingly, an electromagnetic wave propagating from east to west will have a Poynting vector that points in the opposite direction of one propagating from west to east. And correspondingly, the associated cross product, being of opposite sign, must have one of its factors also of opposite sign. Accordingly, if E points up, H must point south for an eastbound wave, but north for a westbound wave. So yes, the direction of propagation can be determined by examining the relative directions of E and H.  However, the problem is somewhat more complex than this analysis would suggest. In the simple case described, the energy densities associated with E and H are equal, and the propagation direction is unambiguous.  However in general a wave may be more complex than that, E and H not necessarily having equal energy densities at a specific point, and not necessarily being at right angles. Two plane waves, for example, could be propagating through one another in opposite directions under the principle of superposition, and in that situation, E x H will be dancing around a lot in nodes and antinodes, with energy jumping from odd-numbered positions to even- numbered positions, sometimes being fully electric and other times being fully magnetic. At any given moment at a specific point,  E x H will have a definite value and direction, which could be referred to as the direction of energy  at that time and place, but it will not match the magnitudes and directions elsewhere, so that one could not speak of the whole wave as having a single direction of energy movement.  All that is a classical view. Trying to interpret this quantum-mechanically raises complications that I am unable to answer, such as, what, under these conditions, is the statistical distribution of photon directions and energies?  A big problem with trying to answer that question is that the question itself may be meaningless in view of the fact that such a wave function may well describe a single photon.

[geordief]

If one detects a wave /photon  is there a possibility that this detection could refer to any wave/photon originating from anywhere in the universe?

A  second detection will reinforce the probability of the  origin  but can never  do so with 100% probability?

[nilak (OP)]

If one detects a wave /photon  is there a possibility that this detection could refer to any wave/photon originating from anywhere in the universe?

A  second detection will reinforce the probability of the  origin  but can never  do so with 100% probability?

Even if the universe is not deterministic as QM says, if you could contain all the information in the whole universe or a smaller version, then you could predict an infinity of possible correct version of what could happen next. It means you could make predictions of the future from a single slice through spacetime like in a computer simulation (I'm not insinuating we are in a simulation and I don't think we are).
The only clue that supports this time asymmetry is the classical EM wave propagation. This may be true for the other fields like thise corresponding to the strong and the weak force. QM cannot distinguish past from the future.

[geordief]

QM cannot distinguish past from the future.

If all observers in all reference frames agree that one event precedes another would this establish past from future in the quantum realm?

Am I trying to introduce GR where it has no business?

[nilak (OP)]

QM cannot distinguish past from the future.

If all observers in all reference frames agree that one event precedes another would this establish past from future in the quantum realm?

Am I trying to introduce GR where it has no business?

I don't think it solves the time asymmetry. It is only a consequence of it.

Observers are limited by the information they receive. For example two solar explosions will be seen on Earth later than on Mercury but the succesion of events is the same. This doesn't say anything about the asymety of time in the equation of motion.

[geordief]

I don't think it solves the time asymmetry. It is only a consequence of it.

Observers are limited by the information they receive. For example two solar explosions will be seen on Earth later than on Mercury but the succesion of events is the same. This doesn't say anything about the asymety of time in the equation of motion.

I have been told that there are frames of reference where Solar explosion#1 will be seen AFTER  Solar explosion#2 and frames of reference where Solar explosion#1 will be seen BEFORE Solar explosion#2

I have been told that this is possible in cases where the two Solar Explosions are not connected in a causal way.

I cannot vouch for this. Do you think it is true ?

[nilak (OP)]

I don't think it solves the time asymmetry. It is only a consequence of it.

Observers are limited by the information they receive. For example two solar explosions will be seen on Earth later than on Mercury but the succesion of events is the same. This doesn't say anything about the asymety of time in the equation of motion.

I have been told that there are frames of reference where Solar explosion#1 will be seen AFTER  Solar explosion#2 and frames of reference where Solar explosion#1 will be seen BEFORE Solar explosion#2

I have been told that this is possible in cases where the two Solar Explosions are not connected in a causal way.

I cannot vouch for this. Do you think it is true ?

I don't know about that possibility but this could happen in my opinion only if events are not within the same universe or events within different non radiating black holes but these are speculative thoughts.

[geordief]

I don't know about that possibility but this could happen in my opinion only if events are not within the same universe or events within different non radiating black holes but these are speculative thoughts.

Speculating here too.

Suppose the 2 Solar explosions are at different ends of a line joining Earth and Mercury and on Earth they are viewed as simultaneous, then they must be viewed on Mercury as  being time ordered.

It is not hard to imagine (even though my poor maths would struggle to show it ) that 2  locations could be  chosen nearby to Earth  so that,from one of them  Solar explosion#1 would appear to   precede   Solar explosion#2 and from the other   Solar explosion#1 would appear to   follow   Solar explosion#2.

Similarly with Mercury.

And so  from one set of locations (one near Earth and the other near Mercury) the pair  of Solar explosions would be ordered one way  ,whereas from the other pair they would be ordered timewise "back to front"

Does that seem right?

If that is right it would show that  2 events can indeed be seen to be time ordered differently depending on one' frame of reference (perhaps ,indeed even simply depending on one's location within the same frame of reference)

[nilak (OP)]

I don't know about that possibility but this could happen in my opinion only if events are not within the same universe or events within different non radiating black holes but these are speculative thoughts.

Speculating here too.

Suppose the 2 Solar explosions are at different ends of a line joining Earth and Mercury and on Earth they are viewed as simultaneous, then they must be viewed on Mercury as  being time ordered.

It is not hard to imagine (even though my poor maths would struggle to show it ) that 2  locations could be  chosen nearby to Earth  so that,from one of them  Solar explosion#1 would appear to   precede   Solar explosion#2 and from the other   Solar explosion#1 would appear to   follow   Solar explosion#2.

Similarly with Mercury.

And so  from one set of locations (one near Earth and the other near Mercury) the pair  of Solar explosions would be ordered one way  ,whereas from the other pair they would be ordered timewise "back to front"

Does that seem right?

If that is right it would show that  2 events can indeed be seen to be time ordered differently depending on one' frame of reference (perhaps ,indeed even simply depending on one's location within the same frame of reference)

Yes, but your example, like mine are only visual effects. Some spacetime diagrams are needed to explain the idea. But I don't think you can reverse the order. I'll try to search for some articles about this.

[Colin2B]

If that is right it would show that  2 events can indeed be seen to be time ordered differently depending on one' frame of reference (perhaps ,indeed even simply depending on one's location within the same frame of reference)

At a simple level you can see how this can be true.
Take locations A, B and C and events X and Y

              X.                       Y
A.                        B.                       C

If X and Y are 2 simultaneous flares then B will see them as simultaneous. A will say X occurred 1st and C will say Y occurred first.
This is before you add in relativistic effects.

[nilak (OP)]

If that is right it would show that  2 events can indeed be seen to be time ordered differently depending on one' frame of reference (perhaps ,indeed even simply depending on one's location within the same frame of reference)

At a simple level you can see how this can be true.
Take locations A, B and C and events X and Y

              X.                       Y
A.                        B.                       C

If X and Y are 2 simultaneous flares then B will see them as simultaneous. A will say X occurred 1st and C will say Y occurred first.
This is before you add in relativistic effects.

    These examples are visual effects  only. If you draw newtonian diagrams the order of events is very clear and always the same, in this case always simultaneous like you first defined them.
    As far as I know, Special Relativity does not violate the order of events.
    If you look at  a Minkowski diagram you can see that when fowing the timeline of the main refference frame, a positive interval will always correspond to a positive interval on the moving refference frame time axis.

[Colin2B]

    These examples are visual effects  only. If you draw newtonian diagrams the order of events is very clear and always the same, in this case always simultaneous like you first defined them.
    As far as I know, Special Relativity does not violate the order of events.
    If you look at  a Minkowski diagram you can see that when fowing the timeline of the main refference frame, a positive interval will always correspond to a positive interval on the moving refference frame time axis.

You beat me to it, I was about to add what you just said.
Knowledge of the layout, timings etc allow you to work out what is really happening. This is the same with many so called paradoxes in relativity, when you know what is happening it becomes clear that what you see is not always what you get!