Of Particular Significance

Category: LHC Background Info

This post is a continuation of the previous one, which you should read first…

Now, what exactly are these wormholes that certain physicists claim to be trying to make or, at least, simulate? In this post I’ll explain what the scientists did to bring the problem within reach of our still-crude quantum computers. [I am indebted to Juan Maldacena, Daniel Jafferis and Brian Swingle for conversations that improved my understanding.]

An important point from last post: a field theory with quarks and gluons, such as we find in the real world or such as we might find in all sorts of imaginary worlds, is related by the Maldacena conjecture to strings (including quantum gravity) moving around in more dimensions than the three we’re used to. One of these dimensions, the “radial dimension”, is particularly important. As in the previous post, it will play a central role here.

Einstein-Rosen Bridge (ER) vs. Einstein-Podolsky-Rosen Entanglement (EPR)

It’s too bad that Einstein didn’t live long enough to learn that two of his famous but apparently unrelated papers actually describe the same thing, at least in the context of Maldacena’s conjecture. As Maldacena and Lenny Susskind explored in this paper, the Maldacena conjecture suggests that ER is the same as EPR, at least in some situations.

We begin with two identical black holes in the context of a string theory on the same curved space that appears in the Maldacena conjecture. These two black holes can be joined at the hip — well, at the horizon, really — in such a way as to form a bridge. It is not really a bridge in spacetime in the way you might imagine a wormhole to be, in the sense that you can’t cross the bridge; even if you move at the speed of light, the bridge will collapse before you get to the other side. Such is the simplest Einstein-Rosen bridge — a non-traversable wormhole.

What, according to the Maldacena conjecture, is this bridge from the point of view of an equivalent field theory setting? The answer is almost fixed by the symmetries of the problem. Take two identical field theories that would each, separately, be identical to one of the two black holes in the corresponding string theory. These two theories do not affect each other in any way; their particles move around in separate universes, never interacting. Despite this, we can link them together, forming a metaphorical bridge, in the most quantum sense you can imagine — we entangle them as much as we can. What does this mean?

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON December 6, 2022

With a headline like that, you probably think this is a parody. But in fact, I’m dead serious. Not only that, the discovery was made in the 1960s.  Due to an accident of history, the physicists involved just didn’t realize it back then.

That said, there are profound problems with this headline.  But the headlines we’ve seen this week, along the lines that “Physicists create a baby wormhole in the laboratory”, are actually WORSE than this one. 

It is more accurate to say that “string theory and extra dimensions were discovered experimentally in the 1960s” than to say that “a baby wormhole was created in a lab in the early 2020s.” 

And now I’m going to show you why. As you’ll see in this post and the next, the two claims are related.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON December 5, 2022

Well, now…

  • Did physicists create a wormhole in a lab? No.
  • Did physicists create a baby wormhole in a lab? No.
  • Did physicists manage to study quantum gravity in a lab? No.
  • Did physicists simulate a wormhole in a lab? No.
  • Did physicists make a baby step toward simulating a wormhole in a lab? No.
  • Did physicists make a itty-bitty baby step toward simulating an analogue of a wormhole — a “toy model” of a wormhole — in a lab? Maybe.

Don’t get me wrong. What they did is pretty cool! I’d be pretty proud of it, too, had I been involved. Congratulations to the authors of this paper; the methods and the results are novel and thought-provoking.

But the hype in the press? Wildly, spectacularly overblown!

I’ll try, if I have time next week, to explain what they actually did; it’s really quite intricate and complicated to explain all the steps, so it may take a while. But at best, what they did is analogous to trying to learn about the origin of life through some nifty computer simulations of simple biochemistry, or to learning about the fundamental origin of consciousness by running a new type of neural network. It’s not the real thing; it’s not even close to the real thing; it’s barely even a simulation of something-not-close-to-the-real-thing.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON December 1, 2022

Sadly, the LunaH-MAP mini-satellite (or “CubeSat”) that I wrote about a couple of days ago, describing how it would use particle physics to map out the water-ice in lunar soil, has had a serious setback and may not be able to carry out its mission. A stuck valve is the most likely reason that its thruster did not fire when instructed to do so, and so it has sailed past the Moon instead of going into the correct orbit. There’s still some hope that the situation can be salvaged, but it will take some luck. I feel badly for the scientists involved, who worked so hard and now face great disappointment.

In fact at least four and perhaps five of the ten CubeSats launched along with NASA’s Artemis mission have apparently failed in one way or another. This includes the Near-Earth Asteroid Scout and Team Miles, both of which were intended to test and use new technologies for space travel but with whom communication has not been established, and OMOTENASHI, which is intended to study the particle physics environment around the Moon and land a mini-craft on the surface, but which has had communication issues and will not be able to deploy its lander. It’s not clear what’s happening with Lunar-IR either.

One has to wonder whether this very high failure rate is due to the long delays suffered by the Artemis mission. The original launch date was at the end of August; batteries do degrade, and even satellites designed for the rigors of outer space can suffer in Florida’s heat and moisture.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON November 24, 2022

A post for general readers:

The recent launch of NASA’s new moon mission, Artemis 1, is mostly intended to demonstrate that NASA’s incredibly expensive new rocket system will actually work and be safe for humans to travel in. But along the way, a little science will be done. The Orion spacecraft at the top of the giant rocket, which will actually make the trip to the Moon and back and will carry astronauts in future missions, has a few scientific instruments of its own. Not surprisingly, though, most are aimed at monitoring the environment that future astronauts will encounter. But meanwhile the mission is delivering ten shoe-box-sized satellites (“CubeSats“) which will carry out various other scientific and/or technological investigations. A number of these involve physics, and a few directly employ particle physics.

The use of particle physics detectors for the purpose of studying the not-so-empty space around the Moon and Earth is no surprise. Near any star like the Sun, what we think of as the vacuum of space (and biologically speaking, it is vacuum: no air and hardly any atoms, making it unsurvivable as well as silent) is actually swarming with subatomic particles. Well, perhaps “swarming” is an overstatement. But nevertheless, if you want to understand the challenges to humans and equipment in the areas beyond the Earth, you’ll inevitably be doing particle physics. That’s what a couple of the CubeSats will be studying, entirely or in part.

What’s more of a surprise is that one of the best ways to find water on the Moon without actually landing on it involves putting particle physics to use. Although the technique is not new, it’s not so obvious or widely known, so I thought I’d draw your attention to it.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON November 21, 2022

Two of the most widely reported stories of the year in particle physics,

both depend crucially on our understanding of the fine details of the proton, as established to high precision by the NNPDF collaboration itself.  This large group of first-rate scientists starts with lots of data, collected over many years and in many experiments, which can give insight into the proton’s contents. Then, with a careful statistical analysis, they try to extract from the data a precision picture of the proton’s internal makeup (encoded in what is known as “Parton Distribution Functions” — that’s the PDF in NNPDF).  

NNPDF are by no means the first group to do this; it’s been a scientific task for decades, and without it, data from proton colliders like the Large Hadron Collider couldn’t be interpreted.   Crucially, the NNPDF group argues they have the best and most modern methods for the job  — NN stands for “neural network”, so it has to be good, right? 😉 — and that they carry it out at higher precision than anyone has ever done  before.

But what if they’re wrong? Or at least, what if the uncertainties on their picture of the proton are larger than they say?  If the uncertainties were double what NNPDF believes they are, then the claim of excess charm quark/anti-quark pairs in the proton — just barely above detection at 3 standard deviations — would be nullified, at least for now.  And even the claim of the W boson mass being different from the theoretical prediction,  which was argued to be a 7 standard deviation detection, far above “discovery” level, is in some question. In that mass measurement, the largest single source of systematic uncertainty is from the parton distribution functions.  A mere doubling of this uncertainty would reduce the discrepancy to 5 standard deviations, still quite large.  But given the thorny difficulty of the W mass measurement, any backing off from the result would certainly make people more nervous about it… and they are already nervous as it stands. (Some related discussion of these worries appeared in print here, with an additional concern here.)

In short, a great deal, both current and future, rides on whether the NNPDF group’s uncertainties are as small as they think they are.  How confident can we be?

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON November 4, 2022


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