The second experiment (the "Delayed Choice"), does not necessarily show communication backwards in time either. It shows the same as the first experiment: there is some form of coordination that happens instantaneously. In the Delayed Choice experiment, the photon always takes both paths, also when there is no beam splitter in place. It is just that all the other possible paths disappear instantaneously when the photon is detected. That is the "normal" QM quirk, called the measurement problem. Measuring a photons collapses all possible outcomes into a single one.

it helps to look at the photon from einsteins perspective. for the photon itself there is no time passing. the entire path was taken in one moment. the photons moment is projected into the world we experience as a line. but from the perspective of the photon there is no before or after in relation to points on the photons way. the entire way is one single moment for the photon. so the 2nd beam spliter is either present in the moment or not. what we experience as paradox can be simply explained by the relativity of simultaneity

I love that you have branched into incorporating theoretical physics and quantum topics. Huge fan of everything you put out, thanks for teaching me so much🤙

Thank you so much for this my entire life I thought spin meant the partical was actually spinning this makes so much more sense now, thank you so much

I remember when you questioned how we'd feel about you touching on topics other than planets outside of earth yet in our solar system. I'm happy to see you expanding your options for content

Sounds like you're describing the Grand Old Duke of York. _"When he was only half way up, he was neither up nor down."_

Just listened to Einsteins biography audiobook. The one sentence stuck with me:" even Einstein's mistakes are better than today's newest findings."

Thank you for breaking things down in an easy to understand way.

Sabine Hossenfelder made a video sometime in the recent past where she explained why the delayed choice experiment is not sending information back in time.

Loved the slightly longer video, and the topic was very interesting as well. Keep up the good work!

When I first started studying QM my reaction was "what's going on? this doesn't make any sense" but now it's been 10 years and my reaction is "What's going on? this doesn't make any sense"

The way you described information travelling back to the first splitter reminds me of the time travel premise in the Primer movie. The box has to be turned on in order to travel back to the moment it was turned on.

In the delayed choice experiment, the first beam splitter creates two probable paths for the photon quanta to take with the second beam splitter allowing the two probabilistic photons to interfere with its probabilistic wave before being detected as an interference pattern. If you remove the second beam splitter the photon quanta still travels down both paths with oscillating probabilistic wave; whichever detector that is activated is the photon quanta that had the highest probabilistic wave at the time. So if you add the second beam splitter after the photon quanta passed the first beam splitter there is still two probabilistic paths that the photon quanta is taking allowing it to interfere with itself. This doesn't need backward time travel to explain it.

I saw this video and immediately decided to subscribe to your channel a couple of years ago. Interesting stuff, as always. Thankyou Alex.

You just earned a subscription. Great job! I actually didn't know about the 2006 experiment. That blew my mind!

omg one of the best videos on the topic iv seen. congrats man, really good analogies and really good explanation when there simple shouldnt be an analogy!

Some of my ex girlfriends seem to possess this ability.

One of your best vids so far, wonderful job!

the thing that comes to my head is we need to keep in mind that the "time" that we observe works the way we feel only for us, there are relativistic effects happening, like in the twin paradox or lifespan of particles - generally we know that if we go very very fast, a long travel would feel for us like a short one, cause space looks like it shortens a lot (but only for us, not for a stationary observer) - so technically when something moves exactly at the speed of light, the path shortens to infinitely small (zero?) and time taken for the travel does too, so... what if for us the photon took for example 1 nanosecond to travel through the detectors etc, but for the photon everything happened at once, so there was no "time" to "know" that we add or remove detectors - for us it seems like we interact with the photon but from its pov it all happened in one plank's time length, so it "knew" how and if to split or not because it's like it saw the whole situation not like a movie as we observe it, but as A SINGLE FRAME ;o the life we know can't exist without time but if photons can, we have a new phenomenom to understand

Thank you so much. Your presentations of Bell's inequality and of the delayed choice experiment are outstanding. I have just learned something fundamental about the strange world we live in.

Another fascinating and thought-provoking video. Thank you for using your platform to spread knowledge!

This was SUCH an incredible video. Really appreciate you explaining some of the basic principles around quantum physics and entanglement. Before watching this video, I didn't realize that I had the "classical" understanding of quantum physics, and you allowed me to understand things just a little more deeply. As a complete layperson who finds himself fascinated with trying to learn more about this field, that means everything to me. Thank you :)

Re. the double 50-50 experiment: have scientists tried starting the experiment with two of those 50-50 mirrors, but remove the second mirror after the photon has entered / begun?

Scary stuff, we should go deeper into it

Thanks Alex. That went some way in improving my understanding about this. Excellent explanation

Thank you for breaking things down in an easy to understand way.. Thank you for breaking things down in an easy to understand way..

As usual, I still have no more understanding of Quantaum Physics, thanks to my tiny feeble brain. But, thank you for presenting another incredible video that was entertaining and fun to watch, regardless !

Good video! Also, the Duviri Paradox is going to be incredible!

Awesome video & topic. Thank you for sharing this that was very interesting. I loved it. ❤

Well done. I follow a decent bit of this stuff as a layperson but this was trippy for sure.

Thanks for the update

so you oversimplified the DCQE experiment (because it's too complicated to explain in a video that also covers Bell's Inequality/EPR) to the point that refuting acausal information is impossible. But the answer is no: information does not go backwards in time. What you showed is more like the Elitzur-Vaidman bomb-tester experiment, which is weird--the experiment that is.

Way too hard for me to grasp, but loved your explanations anyway!

Anyway, could a photon's passage through a beam splitter not affect its spin and therefore also the spin of the particle not yet arrived? Would this affect the choice of direction through the splitter for the second particle?

Thank you for the video. There is a hypothesis - a single picture of the universe: When moving and fluctuating in a vacuum, the electromagnetic field in the nodes - Forms quanta of gravity - Which carry the speed of light. Suppose - Can be detected using a mobile, new hybrid - the experience of Michelson Morley, if it is in motion relative to the DGP - the dominant gravitational field, for example in 🚆, as in Einstein's mental experience.

Now when I first heard of the delayed choice experiment, it had a much more, "Spooky action at a distance" affect. I don't remember all of the details as to how the experiment was constructed, however the jist of it was that the "observer" would not get any information until after the photon had reached the screen at the end. If I remember correctly, they may have created an entangled pair of photons at the start. The result was that the implication of the photon going back in time to inform itself that, "IT'S A TRAP"!!, seemed much more apparent. Either way, excellent topic and video. Thank you for sharing.

Freaking fascinating. Nicely done.

Your breakdown of the experiment was very good.

Loved the way you explained this, had me gripped.

My brain was fighting to keep up with all the information near the end of the video only to get thrown off by the burrito at 17:50. Something about time traveling, cool video 👍

It's truly incredible that the wave pattern observed in the double slit experiment is due to the interference of the probability of which slit the particle will pass through. Probability interferes with itself creating a wave pattern.

I love these educational videos!💚💚💚

What explains this is measurement. With the first splitter you’re collapsing the wave function, with the second (if angle of impact is complementary) the light is returned to “close to its original (unaltered) state” which is “wave” A filter, or observer, is merely the elimination of redundant or meaningless and even sometimes contradictory information (like opposing waves that cancel each other out)

Point a to b. what happens is a probability wave trees to point b as a wave. When measured at b. The wave is broken and it becomes real. Absolutely mind blowing! Love the stuff!

Very interesting. I cant say that I have a great grasp of quantum physics but from the small part I do know and from videos I have watched, its all fascinating. I really think that we are missing quite a lot here. The universe is such a beautiful crazy place.

That would mean the information still persists until it hits the detector, and interacting with that information will cause it to collapse. This makes more sense if the wave and particle are separate like pilot wave theory suggests. Then you have waves radiating away from the point particle in all directions, interacting with that wave anywhere along the path before it hits the detector would change the behavior of the particle. It would also allow a single particle to interfere with itself through a double slit.

My brain shorted out a little from that ad at the beginning. I actually watch a lot more Warframe content than astronomy/science. :)

Bell's work has additional underlying assumptions, like statistical independence of certain aspects of the events. Those assumptions could be violated instead of locality.

What if the particles spin in these directions: ↑↑↓↓←→←→ for B and then A starts?

This is your best video yet. Very well put together.

Thank you kindly for having non-adsense at/near the very front/back/both of video, rather than interrupting like TV once the flow has set in. It suggests mutual consideration for the creator/viewership relationship :>

Thank you for explaining how infinite improbability drive works. Remember don't panic.

I'm curious how they measure if a particle is entangled or not to know if they are when calculating the Spin of different directions.

When I was first presented with your three detector positions for the two particles I thought they were arranged on a plane. But I think in order for the other two detectors to still have a 50% chance of each result, they would all have to be at 90 degree angles to each other, as in oriented along the X, Y, and Z axes, respectively. (Otherwise, if they were at something like 120 degrees or just any old random coplanar orientations, I would not expect a 50/50 chance for the other two detectors to get each result after the first particle was "measured".) I'm not sure if I missed you saying that this was the case, or if you did not say it (perhaps assuming it wasn't important or that we'd figure it out on our own), or if I'm simply wrong and *any* difference in detector orientation resets the probability to 50% (which does not seem like it fits with what I know about QM, especially considering how polarization works, etc, and also, how precisely aligned would the detectors then have to be in order to be "sufficiently aligned" to get the "spooky" entangled opposite result? Therefore I doubt I've got this wrong, at least).

Fantastic video as usual in this channel.

There is another explanation that also fits and does not require the future editing the past: super determination. Everything is determined by the interactions that preceded, and “random” is just a quantification of the information that is not available to the observer.

Would you consider doing a video on the Milky Way and the Andromeda Galaxies colliding? That would be an Awesome Video, Thank You!

I'm really starting to like the idea that particles are activated and deactivated. Meaning that particles themselves don't actually travel but transfer their energy to an inactive particle in an assembly line like fashion, as one particle is activated the previous particle is deactivated and we can only detect the particles while they're active with energy. Using this logic could explain why light looks like a wave to us at certain times and a particle at other times, the wave is the energy activating the particles around it and the particle itself is what interacts with us.

My future self has always been communicating with my past self and that is why listening to my intuition has helped me out in so many ways. There are things I know in my present self that make sense of my past self through knowledge of this present, I have always been in communication between my past and future self.

did the photon really stop and go back or did it just reveal it self on the other path when the second splitter activate? i think when an option is possible it is also taken but not revealed until its certain if that makes any sense.

This makes me think we're going to find out that the universe exists in all moments at once, that everything we see sequentially in time is a perception we are bound by.

It doesn't have to choose between taking one path or both paths, right? The photon is always in a superposition of taking both paths no matter what you do before or after it passes the first beam splitter. However, once it arrives at the detectors, the superposition collapses (or expands to encompass the detectors and you as well) so that only one detector detects a photon I don't see the difference to the double slit experiment, there the photon also only hits one spot on the detection screen despite taking multiple paths beforehand

You know I had this theory about a speed so fast it was fast enough that light could not catch up and it was named dark speed in other words it would be so fast that light wouldn’t be seen at that pace making thing look darker. And now you brought this plausible theory of time being the answer of how to get to the point that dark speed. I’ll have to watch more of the video to see more of what you are talking about though.

Warframe as a sponsor? Thats really cool! Played that games years ago and it was great but having not played for so long its pretty much impossible to understand what is new or what im doing at all. That said..its awesome that the game inspired you, it certainly made me interested in space aswell.

After watching this a second time, I suspect that what's going on in the delayed choice experiment is that the photon is *_always_* going down both paths, but if the second beam splitter is not inserted to recombine the wave, then it can't hit both detectors and "pretends" that it took just one path by only being detected at one or the other!

How can you insert emove a beam splitter faster than the light traveling between? I accept the results but don't understand how exactly this experiment is conducted. Perhaps a video on that would be helpful?

I totally love the video you will release in three weeks.

Best video explaining this phenomenon that I have seen.Thank you

I've had personal experience with "information" being passed back in time without any paradox on multiple occasions. Several times in my life I've experienced strong phantom pain in areas of my body that would months later have a reason to feel like that. The First Time it happened my wrist suddenly spasmed in pain for a few days then about 3 weeks later I broke that wrist in a BMX stunt gone wrong. The last time it happened was the scariest as it resulted in hospitalization and overnight observation with severe chest pain and sharp pains to my inner left groin. Was released clear of heart complications with doctors baffled as to the cause of my chest pain, something that was repeated later down the track. Cue Xmas day and an electric RC car cable of reaching 70km/hr with Broken front suspension and steering. Being unaware of the previously mentioned problems I attempted a manoeuvre that was meant to be driving from the middle of a park to the gravel road Infront of us that was meant to be a slide turn into a donut on the gravel. Instead it plowed into my left ankle tearing my groin in the process flipping me in the air landing on my left side breaking 4 ribs, my hip and crushed the bursa in my shoulder. 2 of the rib breaks were displaced fractures of the 4th & 5th ribs fraction of a millimetre from the bone cartilage join, to close for a normal see. Come to think of it most of the Temporally Referred Pain (TPR) I've suffered from seems to be self inflicted.

What if observing a particle doesn't create it, but summons a predefined one that exists outside of time... or on the 4th dimension. Much like a circle will pop in and out of a 2d world when a 3d sphere passes through it, a certain version of the particle shows up when it's 'observed', making it seem like it was decided on the spot, when in fact it already existed outside the 3d plane, but it just had no reason to appear. Idk just guessing.

Gotta love youtube recomendations, one second you're chilling, the next you're learning about quantum theory.

Entanglement is like going to see a tree in a field at some point in time and establishing the reference that it is standing. The equivalent of you and your friend agreeing on who pays. If you learn later in some way ("observe") that it has fallen, you can deduce (by "entanglement") that it would have made a sound to a nearby observer in that time frame between when you saw it and now ("uncertainty"). A bit abstract but makes the key point that in acquiring the information, nothing "magical" happens, it appears "instantaneous" because the realization happens "now", but the states were and always have been predefined (at creation), you just hadn't observed either of them yet.

In other words, if you can control which way the particle spins, you can communicate faster than the speed of light, assuming the other particle is where you want to communicate to. Because it inherently knows what the other particle is doing, all you have to do is change to rotation back and forth in Morse code. I imagine in the future, submarines will use quantum Morse code to communicate. Furthermore, I can’t imagine that you could intercept a quantum message like that making it even more valuable.

Alex, you are GOLD. Such high quality voice, presentation, script, delivery and visuals. You should be on mainstream TV, your show would make you a very wealthy man indeed - or perhaps you already are?!.. You are a gift to us, and by far one of the best channels covering and explaining these complex subjects for people with basic to intermediate knowledge. Thank you man.

Excellent job and good graphics to breakdown the concepts into layman's terms... 👏👏👏

the energy of the particles have such a small energy , they are influenced by the energy of the consciousness of the observer or the observing tool . Its as the particle is molded by the observing tool .

Great video explaining those experiments. I have a question. How the heck did they add a beam splitter after the photon was sent? That's some faaast sleight of hand! :-)

What this suggests to me is that the particles whos spin is measured are BENEATH Some foundation of physics. Like how dark matter doesnt interact with baryonic matter a similar situation occurs with entanglement.

A coin has 2 sides. It's in a quantum state until I flip it and it lands either heads up or tails up. As the sides are entangled ( opposites) it makes no difference if the coin is a thin dime or a thick nickel. Once it is known which side landed up, we can predict with high certainty which side is facing down.

7:38 Great Scott, it's a flux capacitor!

if they are making it up on the spot then by rechecking the particles repeatedly you should get different results with each check. you can't ignore exceptions as they are still results.

Extremely fascinating! From another of my topics of great interest, I draw a parallel. Virtually all those who have experienced a near death experience (NDE) (and let's just take the hundreds that can be documented as having truly died and then verified information they could not possibly have sensed during their deaths - like detailed events outside the operating theatre) indicate that time and space are illusions and that this 3D world we "live in" is itself, an illusion. They all insist that this world serves as a sort of simplified stage on which we play a role for a short time in order to learn. When you think about it, learning can only happen when there are consequences, and these can only be experienced in a realm with time. If these NDE'ers are right, then our detection of sub-atomic particles is nothing more than us detecting bits whose real nature is beyond our own limited 3 dimensions and time. Much like a 2D person from flatland (in Abbott's great analogy), when encountering a 3D sphere passing through his world, see a dot becoming a circle, growing, then shrinking to a dot and then disappearing and thinking it utterly amazing. The only reason we think it strange when subatomic particles seem to be independent of time or space is that we are constrained to our 3 dimensions and time. We know only that world. But I have a hunch there is much more... If only science would borrow from other areas of study instead of focussing on their own siloed topics and methods. NDEs are now so well documented that they are the becoming the popular study material of numerous doctors and philosophers - something untouchable a mere 20-30 years ago.

With both beam splitters inserted, is it really 50/50 for a photon to hit one detector? My understanding of probability is that it is 50/50 through the first detector, but then probabilities are multiplied for independent events, meaning it is only 25% probable it will arrive at a particular detector. There really IS more flexibility here with two detectors and I suspect the probability becomes variable between 25% and 50% for arriving at a particular detector? It is partly random. Any thoughts?

Yes, time travels in both directions at same time. Take a key ring with key on it. Put another key in, but before continue put key already on ring in also. Then complete. One goes on and one comes off, yet both traveled exact same path in the exact same way. Phone signals internet, electric power lines, tire pushes against road, road pushes back. Energy flows both ways.

but why is this such a big deal? Aren't quantum particles supposed to travel at the speed of light? If so, they don't experience time, so from their perspective, no time has past whatsoever.

Einstein: God does not play dice God: 🎲🎲🎲🎰

Thank you for another great video!

The image of the burrito at the end without acknowledging it was hilarious

Wow this is crazy. Imagine what we could do with this.

If you crash two billiard balls together the total momentum before is the same after. if you look at the momentum of one ball after the collision you know what momentum of the other without looking at it. What's the difference are the billiard balls entangled 😂

I think the beam splitter is acting like a double-slit. Think of it. In splitting the beam, it makes the wavefunction go to both detectors, causing an interference pattern.

Great and interesting explanation. Thank You.

In the past humans have often believed our sight was a sense that threw a mold over the world and allowed us to perceive it, like something invisible until you throw paint on it, revealing its location. It'd be interesting to know for certain that theres truly no offect in us looking at a particle

It happens. He started all of this. Give him credit. We learn new things all the time

The backwards time aspect on the second experiment might be due to the photon traveling at the speed of light, maybe that one theory of photons existing for the entirety of their path is true, so something altering the previous section of their path could affect future travel across that path, since it's still within the timeframe of the photon's existence.

Didn’t expect a Warframe sponsor. Not a bad choice of a channel to sponsor

Quantum mechanics to me is the physical proof that this world is created by an intelligent designer. Call it god or the simulation programmer or whatever.

What's really crazy is that all these geniuses at colleges across the world can KNOW all these intricate theories and yet can't give you the definition of a man or a woman. Really makes you wonder.

Perhaps there’s a reference frame where it actually appears that the second detector is first? Where/when would that defence frame be? Perhaps the physical is connected through the conceptual through time, and our observation of this video is the reference frame where the second detector is deployed first. The act of conceptualization may be a time wormhole, if you are of the believer that there is something continuous about consciousness? If your consciousness is the same at different moments (or a portion of the self is continuous), perhaps its concepts transcend time to maintain their logic coherence? Maybe that’s how our future observations might pass signals through time? Time doesn’t seem to be fundamental, it seems to be an observer dependent illusion constructed by analyzing ratios of among various signals and patterns. The way we look at digital audio. If each observer is a frequency, Nyquist theorem would explain relativity in its own analogous way.

According to new explanations there is no communication backwards in time. See: "The delayed choice" of Sabine and "Boys, was I wrong" of Arvin Ash, and the first part of "Photons, Entanglement, and the Quantum Eraser" of the science asylum (Nick Lucid) and more. If I get it right, the photon always passes through both paths. If no splitter, it interferes with itself such that it always continues to the detector of the same direction. When splitter is added the splitter simply chooses part of the beam to each detector to get the impression of interference pattern.