I think that EDGES probably didn't see a real signal is more or less the expectation of the field. I remember that the feelings towards the result at the time was quite sceptical, and it seems it didn't take long before someone discovered that the published result wasn't very robust: https://telescoper.wordpress.com/2018/09/03/edges-and-foregr...
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.
They don't necessarily depend on the EDGES result holding up, but may be to confirm/refute it. Even if your experiment refutes EDGES, you don't want to imply EDGES was utter bunk from the start, because if that was so why did you spend so much money bothering to test it? Your funding and project still depends on it having some credibility.
For any physicists reading, I have a question about the Big Bang: Is the standard consensus that the specific physical description is literal or just the closest approximation/visual model we have that matches the data?
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?
> "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.
The idea that the universe rapidly expanded in a fraction of a second right at the beginning is called inflation theory, it's a supplemental modification of the big bang theory and not all physicists that accept the big bang theory also accept inflation theory. There are also some theories that try to explain what there might have been 'before' the big bang, conformal cyclic cosmology for example. Then there's zero energy universe hypothesis, which suggests the universe may have arisen from a random quantum fluctuation - though a fluctuation of what is unclear.
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.
I've proposed a modified gravity theory that you might be interested in taking a look at. If correct, it would answer a lot of these questions. You may look at a pdf of it here:
Not metaphors . We know these are out there — we just don’t know a lot about them. The situation is similar to atoms in second half of 19th century : we knew they are there , we knew some of their properties but only it the first quarter of 20th century we learned how much more there is to learn about atoms
Metaphor probably isn't the right word, but it's not really wrong either. "Placeholder" is also sorta correct but not entirely. Dark matter is a placeholder for an as-yet-unknown thing that interacts with gravity, in the most popular theories. There are less-popular ideas--still given serious study and consideration--like MOND that may some day explain the effects currently labeled as "dark matter". I don't think it's accurate to say "we know these are out there", and if it turns out that MOND or some other alternative explains observations, "dark matter" will turn out to have been fairly metaphorical (or just plain wrong).
We say "dark matter" rather than "weird gravity behavior" because the evidence thus far doesn't just look like gravity being weird. It looks like stuff, actual honest to God stuff, floating around. If MOND is right dark matter does not exist and never did. Dark matter is the name of the actual matter we believe is out there; we could be wrong, but it's not just a generic placeholder.
Atoms is a good example. Are atoms really out there in the way that most people would imagine? ("Electrons orbiting a nucleus of protons and nucleus") Or are they all actually fields of statistical probability or some other concept that is basically impossible to imagine in a physical world but matches our equations?
They're "actually" what QFT says they are, but the rest isn't wrong either. It's not wrong to say "a house exists" because it's actually a pile of bricks in the shape of a house.
Dark matter must be "matter" if it exists, because there's not a category of things that aren't matter.
> 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.
Sure, I guess what I mean is it'd still end up in on the table of subatomic particles whether or not it's a new one.
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.
I'm so excited for JWST's data. Observations from the inflationary period have the potential to completely upend cosmological dogma. Findings like this are the precursor. I'm sure theorists are furiously working on alternative models. This is an exciting period to watch.
Inflation happened during the first tiniest fractions of a second post big bang. No telescope is going to make direct observations of the inflationary period so I'm not sure what you mean by this.
I'm referring to the earliest era of transparent space, when conventional matter supposedly coalesced. If we look back to that period and still see red-shifted mature galaxies then something is very wrong with the current models. I'm under the impression that we don't have good observations of the period 375k-400M years after inflation and that infant galaxy observations have not been confirmed.
The earliest moment of transparent space is the CMB. I know JWST can't detect Pop3 stars, but is there even expectations that it could detect proto galaxies with those stars? I thought it was still much later, like the early Pop2 generation.
> No telescope is going to make direct observations of the inflationary period so I'm not sure what you mean by this.
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?
This isn't just an engineering problem. Photons couldn't move around for the first 380K years or so. Space was nearly uniform, hot, and dense. The CMB is literally the heat wave left over from the point where the heavy soup thinned out just enough to allow photons to fly away in all directions.
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.
> There are some theories that basically say gravity waves permanently "crumple" spacetime
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?
No, you still need something to create the gravity waves. The idea is that once a gravity wave has passed through a region of spacetime it leaves a permanent deformation. In the case of a detector like LIGO this means rather than the mirrors wobbling relative to each other and then settling down to their previous configuration, in fact they are left in a (very slightly) permanently altered configuration. The difference is probably way too small to detect though, for now anyway.
I understand what you're writing (I think), but I don't think I understand how the implications would be consistent with relativity unfortunately. I thought gravity is (supposedly) caused by the deformation of space. If your space isn't flat, then you're going to experience acceleration (aka gravity) at that point, right? And if this deformation is permanent, then its source is already long gone - meaning that when you look down to see why you're falling, you see that there's no matter or energy causing you to fall. Which seems weird to me because I thought you need some kind of matter/energy to cause space to curve (and hence feel gravity/acceleration). Is that not the case?
These distortions are predicted by relativity. They’re a consequence of it, not a problem with it.
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.
You don't feel acceleration either, you feel the normal force of an object against you. If you're in freefall you feel nothing (or really, you do feel the absence of a normal force you're used to).
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.
One problem is that a lot of simplifications get layered on in pop science explanations of relativity, or actually deep science of any kind. We often talk about the force of gravity, but the thing is it's actually not a force, or even a field, in the same way as other forces and fields in physics.
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.
> it's actually not a force, or even a field, in the same way as other forces and fields in physics
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.
The deformations in spacetime are permanent (hypothetically). The mirrors in LIGO, however, are subject to all the other various things in the environment tugging on them. They return to a state of alignment because of their environment (local gravitational forces, etc.) This "noise" would prevent a detector like LIGO from seeing the permanent changes to spacetime.
Yes gravitational wave telescopes is commonly used along with gravitational wave detectors, gravitational wave instruments and gravitational wave observatories.
Well, I guess measurements of the early universe (100-250 million years after the big bang) can test predictions made by models of the inflationary period.
Measurements of pretty much any time in the universe can test predictions made by models of the early universe. One of the main reasons we think there was inflation is from late time (near today) observations of matter density (see https://en.wikipedia.org/wiki/Flatness_problem).
I always found it slightly suspicious how the EDGES dip was right between the ITU region 3 broadcast bands. Obviously they do filtering and are far away from everything, but perhaps the gazillion FM stations in Indonesia + some TV stations + meteor scatter (or some other sort of odd propagation) could maybe escape the RFI filtering and mimic the dip.
Intermod has got to be the real nightmare in that business. There's absolutely no way to guarantee it isn't happening. A rusty bolt on a gutter on a completely unrelated building near a couple of transmitters may be all it takes to re-radiate a signal in a completely different band.
No, these signals are at a low frequency of around 1.4 GHz, not at the high frequencies of infrared or visible light.
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.
I've never heard it mentioned, but I strongly suspect that cosmological redshift is simply the result of photons losing energy over vast distances due to some as-of-yet-undiscovered interaction with the quantum vacuum. It was a couple of vatican-sponsored jesuits with an obvious creationist agenda who turned the observation of redshift into an assumption of spatial expansion to support the theory of a single-point-of-origin universe with a finite age and a finite size. I think western science is predisposed, due to religious cultural influence, to being uncomfortable with an infinite universe, because it implies our own ultimate insignificance.
Science does not suppose a finite or infinite universe, but rather an observable universe of finite size plus an unobservable universe which may or may not be finite in size. Science is a lot more comfortable and accepting of uncertainty and unknowns that you give it credit for here.
This is a reasonable, and i don't accuse all of Science. I am just very suspicious of the certainty with which astrophysics has pursued proof of a big bang for most of a century. There are number of glaring assumptions, many of which point back to an unreasonable level of faith in the Standard Model.
Hah that's great. I can see straight away that I'm going to become a devoted, tunnel vision tired light enthusiast. In fact, i'm tired already. i could use a nap.
No, this is rather a case of the old models probably being the more correct ones: the EDGES result itself was quite unexpected and hard to explain in the existing framework as it was much stronger than expected.
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.
Well, while Chiang may not be involved in either EDGES or SARAS, she's not described as having no horse in the race.
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".
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.