Dark Matter Day Cometh · 3:33pm Oct 30th, 2022
That time of year again. When ponies dress up in Spooktacular costumes for their Nightmare Night fun, and particle physicists thrill everyone with tales of ghost particles and the dark side of the universe.
The story so far:
Fourteen billion years ago the universe began with a Big Bang, which created a primordial hot plasma of quarks and electrons, which cooled into hydrogen gas, which collapsed and ignited into stars, which blew up as supernovae and filled the universe with stardust, which went on to form more stars, planets, pumpkins, ponies, and particle physicists.
But there was something else out there.
The Big Bang also created an enormous number of dark particles. Heavy enough to shape the formation of galaxies through their gravity, but so weakly interacting that most have never hit another particle for billions of years. Dark matter surrounds the galaxy and dominates its mass. Five hundred million of these ghosts pass through your body every second.
But what are they?
There is no shortage of theories of beyond-the-standard-model-physics predicting candidate particles. What we need is an experiment to detect them. After decades of searching using germanium crystals, sodium iodide, sapphire, bubbles of freon, and tanks of liquid xenon, we have found nothing conclusive. It is now clear that they must be very weakly interacting, and to have a chance of seeing one, we need a really big tank of liquid xenon. This is under construction.
Meanwhile we can try to create dark particle by smashing proton beams together at the Large Hadron Collider and searching for the sign of a ghost by the apparent disappearance of energy and momentum. These searches have also not found anything.
The searches continue. Maybe the next generation of xenon detectors will see something. Maybe the LHC will see the signature of something that can’t be explained by known science. Maybe we will see an indirect sign of dark matter through neutrino interactions in the Antarctic ice. Maybe we will just get more null results.
It has become a tradition.
If anyone wants to know more, sign up to join our on-line event on Tuesday 1 November 19:00 UK time: Dark Matter Day 2022: A complete story of Dark Matter, so far...
Or one of the many other Dark Matter Day events going on around the world.
This combination of words delights me more than reason can explain. Clearly the answer to all unanswered questions henceforth must be "we need an even bigger tank of liquid xenon".
5695270
Sadly there are some questions which cannot be answered even with the biggest tank of liquid xenon.
Although if we had a really big tank of liquid xenon and a really big tank of liquid argon, we might be able to address some of those.
What is the relative total rest energy mass of all the neutrinos, compared to that calculated to be due to dark matter? As everyone keeps going on about neutrinos haveing energy but not mass, bu you put enough energy in a volume, and it gets an event horizon, and so much generate a gravitational field, which is a measure of mass?
Wat fortunate to see A Quick Guide To Standard Theory video on YouTube a couple days back, and I will say this. I havent seen a big a wreck of mismatched measurement functions since doing rocketry equations in Imperial measurements. If they really want to find if theres anything beyond the Standard Model, the first thing they should do is work out just what units the various bits should be in so the things coherent.
Personally, Id suspect the E-V or whichever way it goes, should go first. You get your polynomial in total Energy, and that Gives you the Rest Energy, Kinetic Energy, and whatever the next infinity of terms that look like unknown extra energy, mass might turn out to be?
That, and if youre having to constantly multiply by -1 whatever the vector is, it means your measurements are teh wrong way round, like x,y,z should be imaginary etc. Despite how much cosmologists might hate the terminology, its just maths.
And something from maths, is why pull one solution out, when maths doesnt have a preference, all solutions are equally valid at all times, so the result you want is the sum of all those solutions, and you have renormalisation? Like how trig functions are a finite solution between two infinite values far enough up, or you can just take modulo one circle?
The scary thing should be the causality? When you gaze up at the Andromeda Galaxy with the naked eye, those photons being absorbed by your eye have traveled untouched for 2 million years. but, to a photon, no time has passed. Therefore, as far as the last atom tthat emmited that photon is concerned, it couldnt do so until your eye would be in the correct position in the future to intercept the ttoal sum of projected flightpaths of that photonit wants to emit?
Will be an intresting experiment, putting a very short duration decay system in a perfectly illegal state, and see how long it lasts? Or something else happens first.
Really hope someone doesnt try the experiement with Resublimated Theotimilene.
5695281
Just how big are we talking about here? The place where I work has a two story tank of liquid argon. It’s just to store it for certain manufacturing operations that need to be done in an argon atmosphere because nitrogen is still too reactive. The liquid nitrogen tank onsite is roughly twice the size of the liquid argon tank.
5695291
Neutrinos were a dark matter candidate in the past, but have now been ruled out. They do have mass, but it's very small and not enough to explain dark matter. And they move too fast - at relativistic speeds - above the escape velocity for the galaxy. They can't explain the way structures of galaxies formed - this needs a 'cold dark matter' candidate particle - moving at non-relativistic speeds.
5695320
At the moment we need something on the 1-10 tonne scale to be competitive. In the future it will need to be bigger. The real challenge is it has to be radiopure - so a few kilometres underground to get away from the cosmic rays. And as argon has natural radioactive isotopes, you need to source it from deep underground gas fields. Argon is difficult, so at the moment xenon is the leading material, but if we get a signal and need to test it, we will need both.
5695270
I like to think that there's just this one scientist who keeps suggesting it as the answer to every problem XD
5695337
Since one person's opinion makes no difference to scientific enquiry, I must admit I have a soft spot for the braneworld interpretation: that the extra gravitational force is connected to a nearby "brane" universe via gravitational strings, which means their gravitational force "leaks" into ours.
I find it spooky to think there's a universe just next door, and that we're so tantalizingly close we could reach out and "touch" it, yet we don't have the dimensional key that gravity uses to reach through the one dimension needed. Unfortunately, that also makes it practically impossible to confirm, short of figuring out how to manipulate gravity signals.
Failing that, there's primordial black holes as a candidate, even though the number requirements are so tight that their existence looks unlikely. I dunno: ever since I found out about supermassive black holes at the centres of galaxies, I've been more inclined than usual to credit black holes with a larger role in the universe than they're generally given (this might be because of my lingering affection for the "wormhole" concept, or for the low-key fascinated horror I generally feel about the existence of black holes at all).
5695433
Brane theory is very cool, but more in the realm of physics fan fiction than testable hypothesis.