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One of the biggest science news of the last year was tentative evidence that the cosmological constant is not constant. A perfect case of a coonian crisis in science, a clash between theory and data. And the crisis just got worse. The data say that rather than being constant, dark energy was stronger in the past and is now getting weaker. Now, if you've read the news recently, it might not feel like dark energy is getting weaker, but another experiment just strengthened the case. Let's have a look. Dark energy is the name we've given to whatever keeps cosmic expansion speeding up. The easiest way to explain it is with a cosmological constant that one can interpret as the energy of empty space itself which if true means that even nothing has more energy than I do before coffee. Last year we've seen new results most importantly from the dark energy survey and from desi. The dark energy survey looked at how the light from supernovi differs with their distance to us. The Desi experiment looks at patterns in galaxies and galaxy clusters, the so-called berion acoustic oscillations that are left over from sound waves in the plasma in the early universe. Both have found tentative evidence that dark energy is getting weaker in the range of three sigma. That's about a three in a,000 chance that it's a coincidental fluke in the data. And these findings are now backed up by a precise measurement of the cosmic microwave background CMBB for short coming from the South Pole telescope. This is a telescope with a 10 m dish and rather than scanning the entire sky, it focuses on the details in a small part of the sky where they measure both the temperature and the polarization of the CMBB. In galactic coordinates, it's this green patch down here. To put this into relation to the other measurements, the dark energy survey measures supernovi. So these are fairly near to us and quite late in the history of the universe. The baron acoustic oscillations happen in the plasma in the early universe from around 10,000 to 350,000 or so years after the big bang. These patterns then get imprinted into the distribution of matter in the universe. This is what Desi looks for. The CMBB is created when the barrier on acoustic oscillations end. So these are three separate pieces of evidence. The new paper's a summary of the data that the South Pole telescope collected in 2019 and 2020 and it just appeared on the archive. For one thing, they confirm the tension in the hover rate at a stunning 6.2 sigma away from local measurements. But they also confirm the same preference for a weakening of dark energy. that is it was stronger in the past, possibly even stronger than a cosmological constant could ever be. The result has a smaller error bar. However, the significance of the tension with a constant arc energy is about the same as with the earlier measurements in the range of three sigma. This is because their best fit value is somewhat closer to the vanilla cosmological constant. They also combine their data with Desi and say that then the significance increases. Again, it's not a huge improvement, but that said, honestly, I was expecting that I'd have to tell you, sorry, it went away, but it doesn't seem to want to go away. What does this mean? Well, for one thing, if dark energy indeed depends on time, that would also alleviate the Hubble tension. But maybe more importantly, if dark energy is not a constant, this is a clue that it's sort of a field that permeates the universe. And in physics, fields are always linked to particles. This means that either dark energy is made of a new type of particle or it's actually linked to an existing particle, for example, the hix boson. This has been proposed a couple of times in various ways and none of these theories have been very convincing so far. But maybe physicists will now revisit this idea. If this finding turns out to hold and dark energy indeed weakens, this also changes the outlook for the future of our universe. Because if dark energy is constant, then the expansion will just keep on getting faster and faster. But if dark energy weakens or maybe even goes away entirely, this makes it possible that the expansion slows down, the universe might even collapse, making ideas of cyclic universes with recurring big banks more plausible. On my meter, I give this a 2 out of 10. This is because all these parameter fits already assume a particular model for the universe, and maybe the issue isn't dark energy after all, but that we shouldn't be using this model. But if you felt a disturbance in the force recently, it might not be your anxiety. It could just be the vacuum energy dropping or rising, or maybe it's just gas. One of the biggest problems with news today is that you don't just get the facts, you get someone's opinion about the facts. 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