[Bored chemist]

The uncertainty problem is not to do with measurement..

Is that clear enough for you?

[Colin2B]

The diagram from NASA website seems to suggest that there is phase shift between electric and magnetic field in a propagating electromagnetic wave.

I don’t read it that way. I think for graphic effect (3D?) they have displaced the 2 graphs. If you look at the origins of each graph you will see they line up.
Not that it matters, they are only in phase for linear polarisation.

Apologies if someone has already picked this up.

[alancalverd]

There must be a phase shift between electric and magnetic field because each is the time derivative of the other!
NASA is pretty good at maths and physics.
Apart from converting meters to feet, that is.
Or testing spherical mirrors for aberration.
Or freezing O rings.
Maybe I'll withdraw my Mars application after all.
But Maxwell was a Peterhouse man, so  you can trust the phase shift.

[hamdani yusuf (OP)]

He might say that the field is just "bookkeeping", but there must be something that tells the point A that the charge has moved.
He says the charged thing is sending out it's location velocity and acceleration.
But he skips over how that's sent out.
Is it sent by pigeon?
Given that it travels at C, it's hard to see what it could be apart from EM radiation.

When Isaac Newton was asked with similar question about gravity, he said hypotheses non fingo.

[hamdani yusuf (OP)]

The diagram from NASA website seems to suggest that there is phase shift between electric and magnetic field in a propagating electromagnetic wave.

I don’t read it that way. I think for graphic effect (3D?) they have displaced the 2 graphs. If you look at the origins of each graph you will see they line up.
Not that it matters, they are only in phase for linear polarisation.

Apologies if someone has already picked this up.

It looks like a cabinet or cavalier projection. Which means that there is phase difference.


Even in circular polarization, they are still in phase. The phase difference here is between electric field in x axis and y axis.

[hamdani yusuf (OP)]

I think the experimental facts are pretty well established.  And I can't explain them with a wave model.

What makes the photons go into opposite direction, instead of random?
Does it also happen in cloud chamber after a positron is detected?

[Bored chemist]

What makes the photons go into opposite direction, instead of random?

which then produces a pair of gamma rays with a specific energy, and opposite directions to conserve energy and momentum.

Does it also happen in cloud chamber after a positron is detected?

Yes.

[hamdani yusuf (OP)]

What makes the photons go into opposite direction, instead of random?

which then produces a pair of gamma rays with a specific energy, and opposite directions to conserve energy and momentum.

Does it also happen in cloud chamber after a positron is detected?

Yes.

Does the pair always start with 0 total momentum?
What determines the photons direction?

[Bored chemist]

Does the pair always start with 0 total momentum?

From some point of view, yes.
https://en.wikipedia.org/wiki/Center_of_mass#Barycentric_coordinates
You can pick a different point of view if you wish; it makes the arithmetic harder.

[Bored chemist]

What determines the photons direction?

It seems to be random.

[Colin2B]

Even in circular polarization, they are still in phase. The phase difference here is between electric field in x axis and y axis.

Yes, I agree. My mind was distracted and I’m so used go thinking in E fields only I transposed them.

It looks like a cabinet or cavalier projection. Which means that there is phase difference.

I still think it’s an effect of a poor graphic, I would be surprised if the illustrator was thinking cabinet or had been told to put in a phase shift.
If you wanted to show them as out of phase you would either put them both on the same axes or label the z axis to specific points. Have you contacted them to point out the anomaly?

[alancalverd]

Does the pair always start with 0 total momentum?
What determines the photons direction?

The initiating positron doesn't have a lot of kinetic energy by the time it is captured by an electron and the pair are in a much greater mass of medium, so the positron's momentum is mostly transferred to everything else by the time the pair annihilates. You may get some forward scatter if you do the experiment in vacuo with very high energy positrons (using an accelerator)  but when the radionuclide is embedded in a patient the momentum of the positronium is negligible and random.

There is thus no preferred direction for the photons.

[evan_au]

An aside: Isaac Asimov imagined a "positronic brain" for his science fiction robot stories.
- I don't see anything here that makes a "positronic brain" any less infeasible than it was 70 years ago...
- We have had a fast-paced robot movie based on "I Robot" that pretty much ignored the "3 laws of robotics"
- We have had a slow-moving movie based on "Bicentennial Man" that acknowledged the 3 laws of robotics - but was probably considered too boring for most people
- We have an upcoming series based on "Foundation": I wonder how they will walk this difficult line?

Presumably utilizing a minimal quantity of positrons...

[alancalverd]

I think it's a bit like "lightning chess". Given the half-life of positronium at around 100 ps, the positronic brain has to make up its mind very quickly before it is self-annihilated. Darwin took care of its evolution, so there aren't many about but they are very, very clever. Think randy mayfly.

[hamdani yusuf (OP)]

I imagine an aluminum plate 100x100 mm, smeared with water containing ¹⁵O,  and another aluminum plate 100x100 mm on top of it, like a capacitor.



https://en.wikipedia.org/wiki/List_of_PET_radiotracers
Will the gamma ray still generated at random direction? Or they will be more likely directed normal to the plates?
Or the contrary, more gamma ray directed perpendicular to the normal?

[acsinuk]

Just found this article about quantum virtual photons which identifies the magnoflux spin effect.   https://www.sciencedaily.com/releases/2021/07/210721172648.htm?fbclid=IwAR14hMshF2tL73nMYWTq5syKLISrc7k_vgE6IGw1ecCm2ytxWoSRIKQm260

[Bored chemist]

Just found this article about quantum virtual photons which identifies DOESN'T EVEN MENTION the magnoflux spin effect.

FTFY

[hamdani yusuf (OP)]

It's clear that we can't capture all the emitted photons, but the simultaneous capture of two 511 keV photons at 180 degrees is excellent evidence that 2me has been annihilated, and the net charge of the patient remains stubbornly at zero.

Getting similar numbers may indicate some correlation. But it can also be coincident.

A popular Facebook post suggests that the location of the Great Pyramid of Giza is mysteriously connected to the speed of light. It says:

“Speed of light: 299,792,458 m/s. Coordinates of the Great Pyramid of Giza: 29.9792458°N. Coincidence?”

https://fullfact.org/online/great-pyramid-speed-of-light/

Human body is not suitable for investigating basic science since it's too complex with many interacting variables. We could start with simpler objects like what I proposed above. It's unfortunate that I have no access to any PET machine. But it should be easy to do for those who has.   

[Bored chemist]

We could start with simpler objects

They did, and they do.
Did you see  the IOP video at about 03:30... the one you posted?
A nice simple object- a vial with a radioactive sample in it.

[Bored chemist]

I imagine an aluminum plate 100x100 mm, smeared with water containing ¹⁵O,  and another aluminum plate 100x100 mm on top of it, like a capacitor.



https://en.wikipedia.org/wiki/List_of_PET_radiotracers
Will the gamma ray still generated at random direction? Or they will be more likely directed normal to the plates?
Or the contrary, more gamma ray directed perpendicular to the normal?

You do know that water conducts electricity, don't you?
So your idea is impossible.
Why did you propose it?