Photons, Entanglement, and the Quantum Eraser

To clarify: I understand the "detection" at the screen is a different kind than one that might happen at the slits or any other detectors. It was just meant as a segue/transition to the main conclusion of the video: that quantum mechanics is just a model. The way quantum mechanics works doesn't necessarily say anything about the nature of matter/light. If we input some initial conditions and a few interactions, it will give us a result that matches an experiment really well... but only after we do the experiment with a bunch of particles over time. That doesn't mean we can make any judgements at all about what individual particles are doing at any given moment.

So does this mean the photon knew beforehand whether the which-path information would be erased or not?

The photon was created by a laser so in itself it's an inorganic way of measuring its natural state and ability....are there experiments that prove is natural state of behaviour? Are we experimenting to make better lasers or are we actually studying the universal laws of physics?

I find the physicalist cope in the intro quite funny. Better to state the issue as it is though, a mystery.

When your religion has clouded you so much, you start with let's bring QM back to "reality" and then have a maxim of there is no magic. Much like any religious or spiritual junkie you might find yourself almost tantalisingly close to getting thr full hit, the full high, the enlightenment. But just always missing it a tad. The signs are looking hopeful as we move forward that instead of a "theory of everything" we start including literally everything (that's what your religion calls magic, thats anything, otherwise how can it include everything?) And start to feel into everything, using every tool we have available and get back to the unifying thing that we all are anyway, then we might all start having some fun. Some are already doing it. We all can.

How many times can we split the photons?
We have a photon, and we split it into two entangles, pA and pB.
Can we then split just pA into pA- and pA+?
And then take pA- and split into pA-a and pA+a?
You said that pA and pB are both half of the energy of the original photon.....how can we measure that?

And if we really can measure that, and it isn't just a guess, then splitting and splitting and splitting many times over.......would you get a photon that was easier to slow down? Or are we talking about brightness? If we are only talking about brightness, then are they really opposite? I can see that they still have the same speed, so long as they are easier to slow down.....and we know that certain mediums have a greater ability to slow light down.

So, take a photon that has been split 100 times, and see how drastically that can be slowed down....and whether any of the other photons are still entangled....they probably won't be, because of the interaction to split it again

What is the function of the polarizers?
In the end they only allow the following 2 cases for the photon to hit the screen. Either:
1. horizontally polarized photons that came through slit A

2. vertically polarized photons the came through slit B

How does that help in determining the slit used?

Is there another polarizer afterwards that determines the source slit by checking the polarity after passing the first polarizers?

I love it that you are open to the limits of our understanding, instead of doing like many, meaning coming with a favorite random explanation and presenting to the public as the only possible alternative.

I believe a giant part of science is being very aware of what we don't know. Falling in love with an assumption causes way more harm than good.

The thing you didn't explain well... is that the "interaction" of the wave with the polarizer was that the polarizer "blocked" the wave from continuing to the screen. Polarizers do not reorient the wave, they block incompatible waves.

No WAIT.
I don’t get it yet again.
I do understand your explanation of the interference pattern and the pattern with the polarizers and just the normal macroscale pattern.
BUT
I don’t understand why your portrayal of waves changes.
When you describe light as a wave, you speak of waves snaking through the slits. But when you describe light as a particle, it’s a wave that doesn’t undulate at alll rather it slides sideways on some Z-axis.
I THINK in scenario 2, you are talking about a probability wave of where a single photon from a minimally dim light (1 photon’s worth).
But now it seems that in relation to scenario 1, you are describing one wavelength of a wave traveling all by itself.
Maybe that’s it. Is that it?

Correct me if I'm wrong, Nick, but the pattern on the screen is always a non-interference pattern (a big mess), right? However, only when we have information from all the detectors do we use math to separate the screen's pattern into two distinct ones: an interference pattern and a non-interference pattern. Then we discovered that all the photons in the non-interference pattern have their entangled partners detected, rather than erased. Is that correct?
And for this reason, since we must have all the information, it doesn’t violate the speed of light communication or causality?

What if the "detection" was pre-determined, so it already "knew" that it would go through or be reflected?

The double split experiment is an exhibit displaying a wave/particle duality of "probability" relating to the quantum world at a subatomic level. (When it is detected or observed) only the particle can be seen on the exterior wall, each and every time. In this fashion, it collapses.

Ok, Thought experiment. Let's run the light from the lower part of the Glan-Thompson prism not just a few centimeters further than the light from the upper part. Let's let that lower part run, say, to Mars, where it hits a mirror and returns to us. This gives us plenty of time to decide whether we put the eraser here, or a detector.

Now we make that decision based on what we see on the screen in the upper part of the picture. But not in the way it should be - we deliberately make that decision the other way round. How does this not run into a contradiction? 🤔

Then is photon a particle or wave?

no

I appreciate your grounded explanations of these topics.

And yet I still find it magical! Frig the Universe is neat!

The issue here is the assumption that the experiment is actually getting to a single photon. In reality I've seen the technique that reduces the energy to what the math says is a single photon, but it's still propagating as a wave.

Why do you need two polarizers? Seems like one would be enough. What would happen if same polarizer was used over both slits.? Why is energy polarized??? That is something I have never heard explained. Radio waves are also polarized. Is all energy polarized? Could we make nuclear energy polarizers? That would be neat, and very useful!! Why aren’t photons diagonally polarized? Is laser light polarized? Why is any light polarized? Is starlight polarized? Help!!! So many questions. If I wear polarized glasses will I miss something? Maybe that’s why I can’t see ghosts?

Anyone else agree unshaven Nick is best Nick?

How are you going to get clicks if you don't mystify people?

Great job on describing the delayed choice quantum eraser, better than most any other ones I have seen. But, there is an easier way to show this experiment, all you need to do is shine the light through a diagonal polarizer before hitting the screen. Then we lose which-way information. It is still delayed from where the “interaction” occurred at the slits.

Does the Pass still exist maybe😮 I don’t think in a way will ever be able to travel to it

Nick just totally slam dunked the mysticism around the double slit experiment with extreme agression. This was VITAL, because as someone who have watched those vids, and been mystified, I needed this snap back to reality. Thanks!

Collapse of the wave function is simply part of
the rendering process which is saving memory of this giant spacetime simulation. Like if you playing game and looking around the landscape which is rendered HD/3D , meanwhile distant objects and objects out of focus like trees are rendered LQ/2D, until you look directly at them

Awesome video! I do feel slightly better about QM!

What if the screen and the detector are so far away from each other (and the photons collide with them more or less at the same time) that the information of whether the location was available (exposed, detectable) or not has to travel faster than the speed of light to reach its pair. Is it ok to have FTL information ? As long as it's not matter going FTL through space I guess it's ok.

Thanks for the video. In another video you claimed that the wave equation was actually a heat equation. Which is it?

We should accept the double slit experiment and the eraser as they are BUT they sound so magic that the same "magic protector structures" from my brain that stops me from accepting " quantim conscience" and "adiabatic Q computers with a LOT of qbits are here", or other crazy stuff, are activated here too. We need your wisdom to get a better description.. in a separate one or two episods if this is not above even your powers. I am waiting for 20 + years for something like these. I had an AHA moment on "Andrea Morello (UNSW) about Quantum Computing" for Quantum Comp,.. but I need something similar for this Double slit and especialy for the Eraser part ..

Photon particles do not exist, a single 'photon' is just a single 360deg cycle

The photon is not a wave (we never detect it as a wave), the distribution of photons (aka probability for a single photon) is.

This feels like something no human will ever understand. That scares me.

If light particle does travel at speed of light, then the past, the present, the future are all the same thing.

“Always a wave” and “not a particle”. How then does the same experiment work for actual particles like electrons, protons, neutrons and entire molecules?

A photon is a wave. A photon is a particle. There is no argument to say that it’s “really a wave but sometimes acts like a particle” since the opposite can be argued equally.

Correct me if am wrong There are countable Photon fired and
the photon is detected always at detector 1 way before it is detected in 2 3 4, after detector 1 has sensed all Photon the available output collected here may not be retrieved as was before after all entangled partical gets detected, will it physically change the recording? Only not if the pattern is the right prediction

I beleive the wave simultaneously:
1) Hit the wall around slits, and...
2) Pass both slits with orthogonal polarizations, and...
3) Both parts of the wave after polarizers hit the screen without interfering with each other, since they polarizations are orthogonal.
And only after that, when the wave has already spread whenever possible, our Universe decide where to "fire" the interaction.
And so, the "particle" is actually not an object, but rather a process (an interaction).

Best explanation ever. Photon is a waive. If the slits are close enough it will go through both most of the time hence the interference pattern on the screen behind it. Everything else is nonsense. By the way, if the act of observing collapsed the wave function then the experimenter would never see the interference pattern on the screen.

In the quantum eraser, how is the crystal that splits the photon into an entangled pair not a detector? It has to physically interact with the photon. At that point the photon is already "detected" isn't it?

But you also say that the Schrodinger equation is "not a wave equation"...

Thank you!

Seems like we are adding mechanisms on top of mechanism increasing the pantheon of complex excuses instead of reducing things into simplification .
Very remanecent of what bogged ancient Greeks down .
We all know we can have a relative super positional point of view for every photo, atom or plank length bit but what good is a Google amount of physics or cosmologies for each observed reality ?

This is a really excellent video that explains the nuance of this topic for a lay audience exceptionally well.

I think this is the most correct view I've seen on particle/wave theory of light. Light is a wave, but the interactions or events happen as particles. To understand the delayed choice experiment I think you must realize that Relativity says that time is relative to the observer, and that past, present future relationships of some events are relative to the observer. Even though the current view is that Quantum Mechanics and Relativity are incompatible I believe that they both take part in the Quantum Eraser experiment. Events only occur in space-time and different observers will not agree on the timing of the events. In our reference frame the experiment contradicts our perception of causality, but light does not see time!

This experiment IS providing evidence of backward causality. Im afraid you didn’t explain this phenomena, you just got irritated that it exists.

One more video like this and I no longer feel like a caveman (hopefully)

Great

In the past, the appearance of infinite values has always signalled a breakdown of our theories, rather than extreme behavior on the part of the universe. It has been a sign of lack of imagination on our part, rather than a property of nature itself. Quote by Thuan

My suggestion is that the infinite values are correct, and that renormalization was a mistake. The infinities are correct.

Follow that and everything starts being a unified theory not a patchwork of solutions on separate specific problems.

My suggestion is that
PHOTONS and ELECTRONS / POSITRONS are the same thing. They are two Versions of the same thing.

Photons create electron positron pairs.
Electron positron annihilate into energy, photons
Let's rephrase.
Photons turn into electron positron pairs under certain conditions.
Electrons and positrons turn into photons under certain conditions.

Photons is the speed of light version.
Positron / electron are the space time version.

Furthermore the electron and positron are entangled and swich back and forth under changing conditions.

Some thoughts ;

Are photons created by electrons or the other way around?

The movement of electrons is responsible for both the creation and destruction of the photons, and that's the case for a lot of light production and absorption. An electron moving in a strong magnetic field will generate photons just from its acceleration.Apr 19, 2016

The fact that pair conversion is more active at higher temperatures is a clue to what could have happened at post Big Bang temperatures

For an electron to quantum jump it needs a photon for energy. Maybe Electrons move continually from photon energy.