Are entangled photons ‘touching’ in time?

[martu]

It is right up to the last sentence which is "complete nonsense" .
There are no messages, i.e. as in information passing between the photons at speeds greater then light.
Entanglement imples instantaneous collapse of the wave function. Instantaneous messages do not make quantutum states entangled. Instantaneous messages do not require that the photons be touching.

What entanglement requires is entanglment of the quantum states. If the quantum states are not intangled then a measurement of one photon will not effect the other photon.

You keep repeating that entanglement requires entanglement which doesn’t explain anything does it?

ETA:
You seem to think that "touching in time" means instantaneous messages (the second to last sentence). This is not true.
If the message speed is finite then the space between the photons means a finite time for the messages to travel.
If the message speed is infinite then it does not matter whether the photons are "touching in time" or not. All messages between any photons at any point in spacetime are instantaneous.

Consider this – we have two hypothetical identical rigid objects A and B and they are touching (spatially). If I push A then B will also be pushed. OK? What is the time difference between the push of A and the push of B?

 

[martu]

Huh? The time axis is always a line, it's an axis. Did you mean the opposite?

No I meant that the time for any event is found on the z axis so if we consider (x, y) to be our spatial plane the time co-ordinate is always at some point (0, 0, t). The event’s spatial location will be at (x, y) so to get a complete description of an event we have the spatial coordinates (x, y) and a time coordinate (t). But we do not plot (x, y, t) we plot (x, y) and separately (t), consider the time co-ordinate as the clock for this event.

That makes no sense. Objects occupy one location at any given time, and that location changes as a function of time. Therefore the trajectory of an object through spacetime is indeed a line, but it's a single line and it's at some angle to the z-axis that's less than or equal to 45 degrees on your diagram.

Consider the simple example of two entangled photons created by Spontaneous Parametric Down Conversion. At the time that the single photon ‘splits’ into two photons we have

p₁ is at location (x₁, y₁)
p₂ is at location (x₂, y₂)

where

(x₁, y₁) = (x₂, y₂)

For simplicity assume that the photons are travelling in opposite directions along the x axis.

To say the photon are at the same point in time and entangled is to say that

t₁ = t₂

until one experiences a new event. They share a clock which moves along the time axis.

So after 1 second we have on the x, y plane

p₁ is at location (-c, 0)
p₂ is at location (c, 0)

but on the time axis we have

p₁ is at time c
p₂ is at time c

touching in time.

No idea what you mean. The photons are flying off in opposite directions AND advancing in time; they are detected some distance away in different places some time after they were emitted.

ct₁ = ct₂

I am running out of words to be honest, I think I’ll have a go at writing this out mathematically.

 

[sol invictus]

No I meant that the time for any event is found on the z axis so if we consider (x, y) to be our spatial plane the time co-ordinate is always at some point (0, 0, t). The event’s spatial location will be at (x, y) so to get a complete description of an event we have the spatial coordinates (x, y) and a time coordinate (t). But we do not plot (x, y, t) we plot (x, y) and separately (t), consider the time co-ordinate as the clock for this event.

I understand those words, but what's the point of following that procedure? We draw these plots so that we can tell where the particles are. Doing things your way we'll have two lines for each particle, neither of which represents its position.

Worse, those lines can intersect or coincide even when the particles are not entangled and never interact. For example two pairs of particles produced at different times at the same point would produce four coinciding lines, even though the two pairs might not be entangled with each other. Similarly two particles that actually coincide and therefore can interact cannot be distinguished from two particles that pass across the same point at different times and therefore cannot interact.

Basically this way of drawing diagrams removes lots of relevant information, which is not the point of making a plot. And we cannot even interpret the one piece of info that two t-axis lines coincide to determine anything, as you can see from that example.

As for the math, it simply isn't the case in standard QM that two entangled particles "coincide", or that the time axis is relevant to them in any special way compared to non-entangled particles. "Entangled" means nothing more and nothing less than that the full state cannot be written as a product of a state for particle 1 times a state for particle 2.

 

[Reality Check]

You agree that the ion and the photon are entangled as the text clearly states?

Yes. Each ion is entangled with the photon that it emits.

Firstly no it doesn’t apply if two atoms are unconnected remember that bit about being at the same place too?

You need to state your concept more clearly then.
Remember that if you state it mathematically then you will have to the prove that an entangled quantum state emerges from your mathematics.
So far you have not even got close to that.

If your concept is that two objects that are ever in the same place at the same time, e.g. the 2 photons in your OP, will have their quantum states magically entangled somehow then the 2 ion experiment proves your concept to be wrong.

The ions are never in the same place. The ions are never "touching in time". But they are entangled.
Thus the formation of entangled quantum states does not need the objects being entangled to be in the same place at any time nor does it need for them to be "touching in time".

This makes the rest of your post (and this thread) moot.

 

[Reality Check]

You keep repeating that entanglement requires entanglement which doesn’t explain anything does it?

It explains everything. It is the entanglement that explains the behaviour of the entangled objects.
Your concept explains nothing. All it is is the assumption by you that something that has nothing to to with quantum entanglement will somehow magically create entanglement. Theory and experiment disproves this.

Consider this – we have two hypothetical identical rigid objects A and B and they are touching (spatially). If I push A then B will also be pushed. OK? What is the time difference between the push of A and the push of B?

Why consider that? It has nothing to do with any quantum entanglemnet experiment. At the point that the measurments are made the entangled particles are not "touching (spatially)".

I will wait for you to come back with the mathematical treatment of your concept before comenting further. It will be interesting to see how you get entangled states from your concept.

My guess is that you will start with 2 systems in pure quantum states, allow them to be at the same position, set t = 0, plug the composite system into Schrödinger's equation and get .... a composite system consisting of pure quantum states!

 

[martu]

Thanks both of you, this conversation has helped me understand a few things. You're both right about the maths and maybe I am trying to use words (badly obviously) to describe the existing maths as you suggest Reality Check, I honestly hadn’t thought of that. It’s one thing to follow the maths (as I can when I read a physics text) it’s another to fully understand it, as you’re both probably aware you don’t really grasp the maths behind something until you use it.

I'll be back with some maths if I can. Thanks again.

 

[martu]

Entanglement is common but the problem is decoherence after the entanglement event hence the complex experiments. Or am I wrong again?

Sorry one final thing I meant to add to my previous post, Reality Check is my statement above correct?

 

[Reality Check]

Sorry one final thing I meant to add to my previous post, Reality Check is my statement above correct?

I do not know.

IMO Entanglement is not common given that it needs the quantum states to be manipulated using things that do not appear often in nature, e.g. lasers, specific configurations of magnetic fields (NMR), etc.

 

[martu]

I do not know.

IMO Entanglement is not common given that it needs the quantum states to be manipulated using things that do not appear often in nature, e.g. lasers, specific configurations of magnetic fields (NMR), etc.

If we assume that events exists where the parties are not entangled we have to conclude that events exist where one, or more, of the conservation laws is violated.

 

[Reality Check]

If we assume that events exists where the parties are not entangled we have to conclude that events exist where one, or more, of the conservation laws is violated.

I do not now what you mean.

There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept). Which one, or more, of the conservation laws is violated in that case?

 

[martu]

I do not now what you mean.

There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept). Which one, or more, of the conservation laws is violated in that case?

Really? What experiments show electrons colliding resulting in no entanglement where decoherence hasn't occurred?

Maybe I am way off here but I thought if any two elctrons collided spin would have to be conserved after the collision. Not only spin but any conserved property hence we can say they are entangled.

 

[Reality Check]

Really? What experiments show electrons colliding resulting in no entanglement where decoherence hasn't occurred?

Maybe I am way off here but I thought if any two elctrons collided spin would have to be conserved after the collision. Not only spin but any conserved property hence we can say they are entangled.

I do not know of any such experiments. But the fact that the electrons are in pure quantum states (not really mentioned in my post) means that they are never entangled to start with and can never be entangled by the collision.

And yes spin is conserved during the collision. So what?
So is energy, mass and charge.

 

[sol invictus]

Entanglement is common but the problem is decoherence after the entanglement event hence the complex experiments.

That's correct.

There are definitely events where "the parties are not entangled", e.g. two arbitary electrons collide (same position, same time and so meets the criteria for your concept).

Actually Martu is correct: they will be entangled in that case.

But the fact that the electrons are in pure quantum states (not really mentioned in my post) means that they are never entangled to start with and can never be entangled by the collision.

I think you're confusing entanglement with mixing here. "Entangled states" usually refers to pure states, and unentangled states can become entangled via interactions.

 

[martu]

Actually Martu is correct: they will be entangled in that case.

Stopped clocks and all that.....

Thanks for the clarification.