[00:00] One of the most popular, if not the most&nbsp; popular, recent ideas on the foundations&nbsp;&nbsp; of physics was just ruled out. It's the idea that&nbsp; entangled particles are actually physically linked&nbsp;&nbsp; by wormholes known as ER equals EPR. Let's have a&nbsp; look. ER stands for Einstein Rosen bridges, which&nbsp;&nbsp;
[00:18] is the technical term for the simplest type of&nbsp; wormhole. EPR stands for Einstein, Podolski, and&nbsp;&nbsp; Rosen who wrote one of the first papers on quantum&nbsp; entanglement though at the time it wasn't called&nbsp;&nbsp;
[00:30] entanglement. The conjecture says that entangled&nbsp; particles are connected by these wormholes. This&nbsp;&nbsp; idea was proposed by Juan Maldacena and Leonard&nbsp; Suskind in 2013. And it's since become one of&nbsp;&nbsp;
[00:43] those phrases that theoretical physicists like&nbsp; because it's vague and sounds deep, but is hard&nbsp;&nbsp; to check. If you remember the infamous episode of&nbsp; a wormhole on a quantum computer, yeah, that was&nbsp;&nbsp;
[00:57] brought to you by ER equals EPR. The wormholes on&nbsp; the quantum computer were supposedly the entangled&nbsp;&nbsp; particles plus some higher dimensional blah&nbsp; blah. But let's not get distracted. The idea&nbsp;&nbsp;
[01:09] that entangled particles are physically linked&nbsp; by wormholes or anything is of course nonsense&nbsp;&nbsp; because entangled particles are not linked.&nbsp; Entanglement is a sort of correlation. It implies&nbsp;&nbsp;
[01:23] no physical link whatsoever. A correlation just&nbsp; means that some observable properties are related.&nbsp;&nbsp; Identical twins, for example, share the same eye&nbsp; color. If you know they're identical twins and you&nbsp;&nbsp;
[01:36] know the eye color of one of them, you know the&nbsp; eye color of the other. That's what it means for&nbsp;&nbsp; properties to be correlated. Knowing the one will&nbsp; tell you something about the other. It doesn't&nbsp;&nbsp; mean they're physically connected. Entanglement&nbsp; is like that. You can of course say, "Ah, look, we&nbsp;&nbsp;
[01:53] just take the mathematics for the entanglement and&nbsp; call that a wormhole." Okay, I admit this isn't&nbsp;&nbsp; wrong. It's just meaningless. I could also call&nbsp; my hair a non-perturbative field configuration,&nbsp;&nbsp;
[02:07] but it still wouldn't converge. If you want the ER&nbsp; equals EPR conjecture to be physically meaningful,&nbsp;&nbsp; then well, you actually need some kind of wormhole&nbsp; there. If entangled particles are really connected&nbsp;&nbsp;
[02:19] by wormholes, then those wormholes should do&nbsp; something more than looking profound on a seminar&nbsp;&nbsp; slide. The authors of the new paper now ask a&nbsp; simple question. Suppose an electron is entangled&nbsp;&nbsp;
[02:32] with something else. If that entanglement is a&nbsp; physical wormhole and the electron has an electric&nbsp;&nbsp; field, then some of the electric field must go&nbsp; into the wormhole. Can we not measure this? At&nbsp;&nbsp; first, the answer to this question seems to be no.&nbsp; Because whatever the wormhole, it's ridiculously&nbsp;&nbsp;
[02:50] tiny. Otherwise, we'd see particles disappear and&nbsp; reappear like popping in and out through portals.&nbsp;&nbsp; But the authors look at a case that we've measured&nbsp; very very precisely. A hydrogen atom. A hydrogen&nbsp;&nbsp;
[03:03] atom consists of just one proton in the atomic&nbsp; nucleus surrounded by one electron. They both&nbsp;&nbsp; have a spin and usually the electron and the&nbsp; proton spin are entangled. The authors now&nbsp;&nbsp;
[03:15] say that if the entanglement is a wormhole,&nbsp; then part of the electric field that spans&nbsp;&nbsp; between the electron and proton goes through the&nbsp; wormhole. that in and of itself is unobservable.&nbsp;&nbsp;
[03:27] However, if you poke a hydrogen atom with an&nbsp; electromagnetic field at the right frequency,&nbsp;&nbsp; you can break this entanglement and create an&nbsp; electron proton pair that is not entangled.&nbsp;&nbsp; The author's point is then that these two states&nbsp; are now different. The one has a wormhole, the&nbsp;&nbsp;
[03:43] other not. And this makes a relative difference&nbsp; for the charge distribution in the hydrogen,&nbsp;&nbsp; which then makes a measurable difference for the&nbsp; energy levels of the electron. And this difference&nbsp;&nbsp;
[03:55] well isn't there. The electron energy levels of&nbsp; the two states entangled and not entangled are&nbsp;&nbsp; perfectly described by the standard quantum maths&nbsp; without the wormholes. Of course, this doesn't&nbsp;&nbsp;
[04:07] entirely rule out the idea. Strictly speaking,&nbsp; it just means that if there are wormholes,&nbsp;&nbsp; then very little of the electromagnetic field&nbsp; goes through them. So they say there's some&nbsp;&nbsp;
[04:19] parameter that must be very small. This is why&nbsp; I have to give the paper three out of 10 on the&nbsp;&nbsp; [&nbsp;__&nbsp;] meter. But that isn't because of the paper.&nbsp; It's because the idea itself was already [&nbsp;__&nbsp;]&nbsp;&nbsp;
[04:31] So of course, you can't rule it out. Now&nbsp; look, the people who work on this will say,&nbsp;&nbsp; "But this is not what we mean by ER equals&nbsp; EPR. It's not a real wormhole. It's just a&nbsp;&nbsp; way to think about the maths." In which case, you&nbsp; know, maybe you should stop calling it wormholes.&nbsp;&nbsp;
[04:49] It's quite easy to predict that this paper will&nbsp; not make a difference and physicists will happily&nbsp;&nbsp; continue publishing about this because it really&nbsp; doesn't matter at this point whether it's got any&nbsp;&nbsp;
[05:01] relation to reality. Still, I wanted to tell you&nbsp; about this paper because it's good to see that at&nbsp;&nbsp; least some people still treat the foundations of&nbsp; physics as the science it once was. In summary,&nbsp;&nbsp;
[05:15] ER equals EPR may be useful as mathematics&nbsp; metaphor or grand writing vocabulary,&nbsp;&nbsp; but as a physical wormhole, it appears to have the&nbsp; experimental visibility of my patients. I do a lot&nbsp;&nbsp;
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