Did Physics Just Lose a Brilliant Idea?

[00:00] One of the most popular, if not the most  popular, recent ideas on the foundations   of physics was just ruled out. It's the idea that  entangled particles are actually physically linked   by wormholes known as ER equals EPR. Let's have a  look. ER stands for Einstein Rosen bridges, which  

[00:18] is the technical term for the simplest type of  wormhole. EPR stands for Einstein, Podolski, and   Rosen who wrote one of the first papers on quantum  entanglement though at the time it wasn't called  

[00:30] entanglement. The conjecture says that entangled  particles are connected by these wormholes. This   idea was proposed by Juan Maldacena and Leonard  Suskind in 2013. And it's since become one of  

[00:43] those phrases that theoretical physicists like  because it's vague and sounds deep, but is hard   to check. If you remember the infamous episode of  a wormhole on a quantum computer, yeah, that was  

[00:57] brought to you by ER equals EPR. The wormholes on  the quantum computer were supposedly the entangled   particles plus some higher dimensional blah  blah. But let's not get distracted. The idea  

[01:09] that entangled particles are physically linked  by wormholes or anything is of course nonsense   because entangled particles are not linked.  Entanglement is a sort of correlation. It implies  

[01:23] no physical link whatsoever. A correlation just  means that some observable properties are related.   Identical twins, for example, share the same eye  color. If you know they're identical twins and you  

[01:36] know the eye color of one of them, you know the  eye color of the other. That's what it means for   properties to be correlated. Knowing the one will  tell you something about the other. It doesn't   mean they're physically connected. Entanglement  is like that. You can of course say, "Ah, look, we  

[01:53] just take the mathematics for the entanglement and  call that a wormhole." Okay, I admit this isn't   wrong. It's just meaningless. I could also call  my hair a non-perturbative field configuration,  

[02:07] but it still wouldn't converge. If you want the ER  equals EPR conjecture to be physically meaningful,   then well, you actually need some kind of wormhole  there. If entangled particles are really connected  

[02:19] by wormholes, then those wormholes should do  something more than looking profound on a seminar   slide. The authors of the new paper now ask a  simple question. Suppose an electron is entangled  

[02:32] with something else. If that entanglement is a  physical wormhole and the electron has an electric   field, then some of the electric field must go  into the wormhole. Can we not measure this? At   first, the answer to this question seems to be no.  Because whatever the wormhole, it's ridiculously  

[02:50] tiny. Otherwise, we'd see particles disappear and  reappear like popping in and out through portals.   But the authors look at a case that we've measured  very very precisely. A hydrogen atom. A hydrogen  

[03:03] atom consists of just one proton in the atomic  nucleus surrounded by one electron. They both   have a spin and usually the electron and the  proton spin are entangled. The authors now  

[03:15] say that if the entanglement is a wormhole,  then part of the electric field that spans   between the electron and proton goes through the  wormhole. that in and of itself is unobservable.  

[03:27] However, if you poke a hydrogen atom with an  electromagnetic field at the right frequency,   you can break this entanglement and create an  electron proton pair that is not entangled.   The author's point is then that these two states  are now different. The one has a wormhole, the  

[03:43] other not. And this makes a relative difference  for the charge distribution in the hydrogen,   which then makes a measurable difference for the  energy levels of the electron. And this difference  

[03:55] well isn't there. The electron energy levels of  the two states entangled and not entangled are   perfectly described by the standard quantum maths  without the wormholes. Of course, this doesn't  

[04:07] entirely rule out the idea. Strictly speaking,  it just means that if there are wormholes,   then very little of the electromagnetic field  goes through them. So they say there's some  

[04:19] parameter that must be very small. This is why  I have to give the paper three out of 10 on the   [ __ ] meter. But that isn't because of the paper.  It's because the idea itself was already [ __ ]  

[04:31] So of course, you can't rule it out. Now  look, the people who work on this will say,   "But this is not what we mean by ER equals  EPR. It's not a real wormhole. It's just a   way to think about the maths." In which case, you  know, maybe you should stop calling it wormholes.  

[04:49] It's quite easy to predict that this paper will  not make a difference and physicists will happily   continue publishing about this because it really  doesn't matter at this point whether it's got any  

[05:01] relation to reality. Still, I wanted to tell you  about this paper because it's good to see that at   least some people still treat the foundations of  physics as the science it once was. In summary,  

[05:15] ER equals EPR may be useful as mathematics  metaphor or grand writing vocabulary,   but as a physical wormhole, it appears to have the  experimental visibility of my patients. I do a lot  

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