Are entangled photons ‘touching’ in time?

[martu]

At the creation of a pair of entangled particles we can say that the time of creation for each photon is equal, that is for a pair of entangled photons p₁ and p₂

t_e1 = t_e2 = 0

where t_en is the creation time of photon n.

Here we’re going to use a slightly modified spacetime diagram, in this spacetime diagram the x axis and y axis represent the spatial dimensions and the time axis, ct, is the z axis perpendicular to the (x, y) plane. The z dimension is suppressed to help us picture what is going on.

Picture the two entangled photons as created at the point (0, 0, 0) and they go in opposite directions along the x axis. So for our entangled photons p₁ and p₂ we can say at the time of emission

(x₁, y₁) = (x₂, y₂) = (0, 0)

And also

(dx₁/dy₁) = (dx₂/dy₂)

Here is the extra step – our time axis is not a plane but a line. What does that mean? Well it means for each event e_n we define it’s spatial and temporal co-ordinates not as (x, y, t) but (x, y) and (t) that is we plot the path of an object through time as a line in the (x, y) plane and a different line ‘up’ the time axis. If your spacetime diagram is on a page our path through time can be represented as a line coming out of the page. All objects move ‘up’ the time axis at the same rate, c.

A consequence of this is that for our entangled pair of photons they travel ‘up’ the time line together, at least until one of them experiences an event. Or to put it another way at any time t_n the two photons will be on the t axis at the same point. Any objects that are created at the same time and at the same spatial dimension are ‘touching’ in time and can, and indeed will, influence the other when a conserved property of one changes, the follows directly from the conservation principle.

Another way to look at it is that the photons share a clock from the event of their creation until one of them experiences another event. Indeed for every event you can consider that a unique point is created on the t axis which ‘moves’ up the t axis. This point is our clock and any objects that share a clock will influence each other, objects will no longer share a clock when they experience another event.

Does this make sense to anyone? We have a violation of locality but only for a very special subset of events where time and space are exactly equal. This is very rare in the universe hence we do not see locality violated often. We also cannot violate causality – the only direction you can go in time is ‘up’ the time axis so even though we have faster than light influence we can’t go back in time at all.

 

[Soapy Sam]

The problem with discussions of this nature is that they impinge so little on "normal reality" that common sense scarcely applies- so it's honestly near impossible for the average person to say what is "sensible in this context" and what is not.

Your argument sounds superficially credible to me, but we need someone who can say if it makes sense mathematically.
(Not that such is definitive, but it does seem likely to be a shade more definitive than a merely verbal argument.)

 

[Reality Check]

It seems to make sense to me. The photons are "touching in time" and separated by space, i.e. they are traveling separately through spacetime.

However quantum entanglement is not really a "conservation principle".

 

[martu]

It seems to make sense to me. The photons are "touching in time" and separated by space, i.e. they are traveling separately through spacetime.

However quantum entanglement is not really a "conservation principle".

Can you elaborate on the last sentence please?

 

[martu]

The problem with discussions of this nature is that they impinge so little on "normal reality" that common sense scarcely applies- so it's honestly near impossible for the average person to say what is "sensible in this context" and what is not.

Your argument sounds superficially credible to me, but we need someone who can say if it makes sense mathematically.
(Not that such is definitive, but it does seem likely to be a shade more definitive than a merely verbal argument.)

Agreed.

 

[Reality Check]

Can you elaborate on the last sentence please?

Quantum entanglement is that measurement of an entangled property of one photon determines the property of the other photon (as in your OP).

A conservation principle is that a system has a conserved quantity at all times.

 

[martu]

Quantum entanglement is that measurement of an entangled property of one photon determines the property of the other photon (as in your OP).

A conservation principle is that a system has a conserved quantity at all times.

Yep and what I was trying to say is that the two entangled photons should be considered as one system until they experience another event because they are 'touching’ in time. This explains how measuring one affects the other no matter how far apart spatially they are.

 

[gnome]

I don't know if this makes any sense, but is it plausible to think of them as the same photon for the applicable time?

 

[martu]

I don't know if this makes any sense, but is it plausible to think of them as the same photon for the applicable time?

I'm pretty sure the maths is OK but whether this answers the questions raised by QM and locality is one for the experts.

To answer your question I don't think so as they are in different locations in space. Same location in time however.

 

[Reality Check]

Yep and what I was trying to say is that the two entangled photons should be considered as one system until they experience another event because they are 'touching’ in time. This explains how measuring one affects the other no matter how far apart spatially they are.

The 'touching’ in time concept unfortunately does not explain this. It also applies to any 2 non-entangled photons and measuring one of these does not affect the other. Think about 2 photons emitted from 2 different atoms at the same time (t_e1 = t_e2 = 0).
It is the entanglement that is the reason for the correlation between the 2 photon measurements.

 

[gnome]

I'm pretty sure the maths is OK but whether this answers the questions raised by QM and locality is one for the experts.

To answer your question I don't think so as they are in different locations in space. Same location in time however.

I'm thinking of the same photon, simultaneously located in two different places (effectively).

I have no idea if this image is at all useful.

 

[martu]

The 'touching’ in time concept unfortunately does not explain this. It also applies to any 2 non-entangled photons and measuring one of these does not affect the other. Think about 2 photons emitted from 2 different atoms at the same time (t_e1 = t_e2 = 0).
It is the entanglement that is the reason for the correlation between the 2 photon measurements.

Those two photons are not created at the same point (x, y).

 

[Reality Check]

Those two photons are not created at the same point (x, y).

Neither do the entangled photons have to be (as in your example).
Quantum entanglement of particles does not require them to be in the same location at some point in time, e.g. Experiment demonstrates quantum entanglement between atoms a metre apart.

 

[martu]

Neither do the entangled photons have to be (as in your example).
Quantum entanglement of particles does not require them to be in the same location at some point in time, e.g. Experiment demonstrates quantum entanglement between atoms a metre apart.

That does require that the two photons emitted are at the same point at the same time namely in the beam splitter.

Let’s see if I have understood that article. We have an event at the same point in time and space where the photons are emitted by the ions creating an entangled state between one ion and one photon. Then when the photons ‘mingle’ at the beam splitter there is a chance that the two photons will be entangled. Conclusion - every time there is an entanglement ‘created’ between two objects they are at the same point and time.

Is this in error?

Are there any experiments where two entangled particles do not ‘touch’ each other spatially at all? Yes I get that these two atoms aren’t touching but they are in an entangled state with photons that do touch.

 

[martu]

I'm thinking of the same photon, simultaneously located in two different places (effectively).

I have no idea if this image is at all useful.

That would mean that this one photon had two paths through spacetime which I do not think is permissable but I may very well be wrong, I'll see if I can dig anything up about this. One of the physicists here may know the answer to this immediately.

 

[martu]

I'm thinking of the same photon, simultaneously located in two different places (effectively).

I have no idea if this image is at all useful.

Actually thinking about this a different way if it was the same photon what would it's spin be?

 

[Reality Check]

That does require that the two photons emitted are at the same point at the same time namely in the beam splitter.

Let’s see if I have understood that article. We have an event at the same point in time and space where the photons are emitted by the ions creating an entangled state between one ion and one photon. Then when the photons ‘mingle’ at the beam splitter there is a chance that the two photons will be entangled. Conclusion - every time there is an entanglement ‘created’ between two objects they are at the same point and time.

Is this in error?

Yes that is in error.
The experiment produces 2 entangled atoms not photons. The atoms are never in contact. They are in 2 different magnetic traps over a metre apart.
The photons in the experiment are used to demonstrate that the atoms are entangled.

 

[martu]

Yes that is in error.
The experiment produces 2 entangled atoms not photons. The atoms are never in contact. They are in 2 different magnetic traps over a metre apart.
The photons in the experiment are used to demonstrate that the atoms are entangled.

No it produces entangled ions and photons it says so clearly in the text:

…collapses the wavefunction into a state in which the two ions, as well as the photons, are entangled with each other.

I take it there is something I am missing here?

 

[sol invictus]

There's no reason why two entangled particles ever had to occupy the same spot. There's also no reason why two non-entangled particles couldn't be produced in the same place at the same time (to as much accuracy is entangled particle pairs sometimes are).

So it's hard to see how this idea would work, even if it were necessary to explain something.

 

[martu]

There's no reason why two entangled particles ever had to occupy the same spot.

Is this opinion based on theory or experiment?

There's also no reason why two non-entangled particles couldn't be produced in the same place at the same time (to as much accuracy is entangled particle pairs sometimes are).

How could we know they weren't entangled? How could you produce a pair of non entangled particles at the same point wont you violate conserved properties for the system?

So it's hard to see how this idea would work, even if it were necessary to explain something.

I think the idea that two or more particles can be at the same unique spot in time no matter how far apart they are could explain entanglement don't you? Completely theoretically mind you, I am well aware it seems to be wrong.