Four years on, new experiment sees no sign of ‘cosmic dawn’
quantamagazine.org
quantamagazine.org
The people from the follow up instruments are very polite about all this, which I guess makes sense if you've used the EDGES result to get money for your own antenna.
Do you work in that field? I've always read that competition is pretty brutal in natural sciences.
I ask because I was in my 30s before I learned that Dark Matter and Dark Energy are effectively metaphors. There is something that contributes more gravity in the universe than our understanding of the it predicts. And there is something that contributes energy to accelerating the expansion of the universe, and we have no idea what. So we call them "matter" and "energy" but TECHNICALLY they don't have to be right? It could also be that something exists that is completely beyond our bounds of understanding.
I ask because this feels very much the situation with the Big Bang. Even if all the data shows the universe rapidly expanding in fractions of a second, it is incomprehensible to understand where the energy for it came from, or what happened "before". And the answer "nothing happened before because that's when time started" feels like an acknowledgement of the limitations of our human understanding.
So here's my follow-up question: Obviously we build an understanding of the universe based on observations of the data. And sometimes the data doesn't match and we have to upgrade Newtonian Physics to Einsteinian, or introduce Quantum Mechanics, etc. So are there comparable/equivalent investigations/experiments going on today that reveal numbers/observations that are basically fundamentally unexplainable without looking beyond the realms of our understanding of the limitations of our universe?
Dark matter must be "matter" if it exists, because there's not a category of things that aren't matter.
I mean, ehhh? Like, yes, absolutely, no matter how weird dark matter turns out to be it's the obligation of our definition of matter to adapt to it, but it's also not the same kind of category error as saying atoms don't exist. Depending on how weird gravity's integration into QFT is, dark matter could be arbitrarily divorced from what we expect matter to behave like. If, horror of horrors, there is no such integration, I'd say it's fair to call dark matter something truly other.
Maybe if it's something like another universe of stuff that only interacts with ours through gravity then we'd just be unable to find out which kind of stuff it is? But I don't know how we'd even get to that point.
So there are quite a few alternative variations on big bang theories. The observation that the universe is expanding seems solid, and the detection of the cosmic microwave background means something must have happened long ago that blasted out all that energy, seemingly everywhere at once. When you go beyond those though things start to get less certain.
> "nothing happened before because that's when time started" feels like an acknowledgement of the limitations of our human understanding.
"Nothing happened" is not the correct answer. The correct answer is that we don't know what happened because before you get to the big bang, our current theories of physics stop working. If you run the equations of general relativity backwards from current conditions you get to a singularity and at that point you can't go back any further. That singularity is called the "big bang". But we know that this is (almost certainly) not an accurate model of what actually happened because we know that GR is (almost certainly) just an approximation of some as-yet-undiscovered theory of quantum gravity, just as Newtonian mechanics is an approximation of GR (in the case of weak gravitational fields).
> So here's my follow-up question: Obviously we build an understanding of the universe based on observations of the data. And sometimes the data doesn't match and we have to upgrade Newtonian Physics to Einsteinian, or introduce Quantum Mechanics, etc. So are there comparable/equivalent investigations/experiments going on today that reveal numbers/observations that are basically fundamentally unexplainable without looking beyond the realms of our understanding of the limitations of our universe?
They're trying. The big problem is that all of the low-lying experimental and theoretical fruit has been picked, and doing experiments that will actually advance fundamental physics (i.e. whose outcomes cannot be predicted accurately by GR and QFT) is fantastically difficult. The math turns out to be really hairy too. No one has been able to figure out out to quantize gravity so that GR and QFT can be combined into a single theory, let alone propose an experiment that could test such a theory. It's a major problem, almost at the level of a crisis. Fundamental physics essentially has made no progress since the standard model was finished 50 years ago.
Isn’t this an engineering problem and what we are attempting to do with gravitational wave detectors?
I know at one time it was believed gravitational waves were detected that provided direct evidence for inflationary theory but then the data was determined to be dust from the Milky Way. I thought this was still one of the major ongoing efforts in gravitational wave detection, was this ruled out?
The gravitational waves from those events would have already warped space, and the ones just now reaching us would be from the edge of the observable universe, and so too weak for any instruments we could conceivably build in the next few decades. Not that we shouldn't try, mind you. There are new frontiers in quasimatter and time crystals that could yield far more accurate gravitational wave detectors.
Also fascinating would be to attempt to decipher the deformations left in the metric already. There are some theories that basically say gravity waves permanently "crumple" spacetime, and it might be possible to read signatures of such events if this is so.
Does that mean those theories predict you can achieve permanent gravitational effects (locally) without any matter or energy to cause it? Wouldn't that violate relativity?
Objects influenced by a gravitational field don’t feel an acceleration. Astronauts in orbit round the earth don’t feel anything even though they are going round in circles. It’s only when something gets in the way that you feel an acceleration from the thing stopping your trajectory, like the surface of the earth.
The distortions were talking about are created by a mass though, the mass that created the original gravity wave.
We don't feel velocity but we do feel acceleration, whether it's due to gravity or anything else. I still don't follow the logic unfortunately.
However, that's not what the comment you replied to was saying. Gravity doesn't apply a force at all! A force is when your worldline gets pushed around, but an object undergoing gravity is actually still going "straight", it's spacetime that's deformed.
This is why Einstein is so revered in Physics. He didn't just explain a force, otherwise why would he be given pre-eminence over Maxwell who explained electromagnetism? Relativity is something else completely.
Here's a really good explanation of what's actually going on when gravity influences an object. Hold on to your chair.
That's why (for anyone who's still reading this old thread) gravity is treated separately from the other three "fundamental" forces. We can explain pretty much everything in physics with the tools of Quantum Field Theory, even if there's still some gaps, but relativity is a whole other ballgame. Not only is it totally resistant to the mathematical techniques (quantum operations are linear, relativity is very much not, to name just one issue), but it's sort of unclear what QFT looks like without spacetime as a stage to act on. If the properties of spacetime emerge from some simpler, presumably more quantum, system, we have next to no idea how.
https://www.quantamagazine.org/gravitational-waves-should-pe...
> they are left in a (very slightly) permanently altered configuration
I'd expect that it's a matter of when, not if. See references below:
https://www.upi.com/Science_News/2021/05/19/nasa-moon-astron...
https://www.space.com/moon-far-side-radio-quiet-telescope-pr...
https://www.science.org/content/article/could-humanity-s-ret...
https://earthsky.org/space/lunar-crater-radio-telescope-lcrt...
Seems like we're on the brink of potentially the most significant scientific discovery since Copernicus, or are about to feel awfully stupid.
For such radio signals, much larger antennas are needed than what we can expect to have on space telescopes in the near future.
A much more likely improvement, compared to what can be done on Earth, could be obtained by building a large radiotelescope on the Moon (i.e. with a large array of antennas), on its hidden face.
How does that theory explain the blue shift of Andromeda?
Apparently, this result implies new information about dark matter.
Now that EDGES looks to be dead, the old predictions of a weaker effect are validated.
“a radio astronomer at McGill University in Montreal who wasn’t involved in either experiment, says that both EDGES and SARAS were extremely thorough in their calibration and analysis procedures, and that it’s too soon to say which result is correct. “The level of disagreement is enough to make people uncomfortable, but I think it’s far from the end of the story,” she said. “From my perspective, it adds to the excitement.”
And
“Stranger still, the dip was very pronounced, suggesting that hydrogen in the early universe was colder than theoretical models predicted, possibly because of exotic interactions with the dark matter that fills the cosmos. Or perhaps the EDGES dip had a more mundane origin.”
The article seems to imply that the EDGES dip may be due to mundane, faulty experiment design, instead.
In any case, a little bit of excitement for those scientists.
Rather she's said to be late to arrive with her horse: "[Chiang is] leading another follow-up experiment called PRIZM that will operate on a small island 1,000 kilometers off the southern tip of South Africa".
What does this even mean?