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Webb and Hubble confirm Universe's expansion rate

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Re: Webb and Hubble confirm Universe's expansion rate

#221

Post by luc4sdreyer »

pigpang wrote: post #193
harywilke wrote: post #42

Dr.Becky goes over this in a video [0] from a year ago about the divergent results obtained by the two main ways we measure the rate of expansion. Cosmic Microwave Background Vs. Supernovae. As the accuracy of each method has improved, the end results have diverged. [0] 'theJWST just made the "Crisis in Cosmology" WORSE' https://www.youtube.com/watch?v=hps-HfpL1vc&t=858s

Unfortunatelly, title of article on HN contradicts content of article, so many HN readers skip article because of "confirmed" (in other words: nothing new). IMHO, a Tired Light theory will better explain facts, but it will require paradigm shift, so there will be a lot of resistance before revolution.

> but it will require paradigm shift, so there will be a lot of resistance before revolution.

I think the main point of resistance is the incompatibility with observations. All Tired light models have been falsified: https://en.wikipedia.org/wiki/Tired_light#Specific_falsified...

If you're aware of a model that can fit some or all of our observations, please share it!

Re: Webb and Hubble confirm Universe's expansion rate

#222

Post by denton-scratch »

1d22a wrote: post #161
pdonis wrote: post #118

Earlier quoted context omitted.

Meaning, why did the expansion change from decelerating to accelerating a few billion years ago? Because that was when the density of matter, which had dominated the dynamics until then, became smaller than the density of dark energy, which has dominated the dynamics since then. The dark energy density doe not change with time, but the density of matter decreases as the universe expands.

How is is that dark energy density does not change with time? Surely the total amount of dark energy has to be constant (energy can't be created or destroyed, and all that), and then as the universe expands, that's then the same amount of energy over a larger volume, right?

/me not a cosmologist.

I think the story is that dark energy is indeed created, in the new emptiness resulting from the expansion of space.

I believe it's supposed to be spacetime that expands, not 'space'. But it's beyond me to explain what that even means; as I understand it, spacetime refers to the whole Universe, across all of time. To 'expand' means 'to become larger over time'. But if the thing that's expanding includes time itself, then I'm bewildered.

Re: Webb and Hubble confirm Universe's expansion rate

#223

Post by denton-scratch »

pigpang wrote: post #207
lp4vn wrote: post #150

Earlier quoted context omitted.

As I understand it, before the big bang the whole observable universe was contained in a small sphere and then it started to expand metrically. Is this interpretation correct? Another thing: suppose I point a laser beam to the space and by chance this laser beam never finds any kind of matter in its way, where is this laser going to? To an infinite void? Is it correct to say that stars radiate energy to the infinite…

It's just an interpretation. Your interpretation is similar to the Big Bang model of visible Universe expansion. If you can convince us that your model is better than other models, then we will use your model, but nobody can prove than a model is correct, unless we will find a hidden recorder somewhere which was turned on for few dozens of billion years. Photon will hit something, or will travel until it will be reds…

> (photon is a wave, so it waves something)

That sounds suspiciously like postulating the 'ether'. Surely what a photon 'waves' is the electromagnetic field, which is not a medium, and which fills the whole of spacetime. There is no 'end of the medium'.

Re: Webb and Hubble confirm Universe's expansion rate

#224

Post by mr_mitm »

1d22a wrote: post #161
pdonis wrote: post #118

Earlier quoted context omitted.

Meaning, why did the expansion change from decelerating to accelerating a few billion years ago? Because that was when the density of matter, which had dominated the dynamics until then, became smaller than the density of dark energy, which has dominated the dynamics since then. The dark energy density doe not change with time, but the density of matter decreases as the universe expands.

How is is that dark energy density does not change with time? Surely the total amount of dark energy has to be constant (energy can't be created or destroyed, and all that), and then as the universe expands, that's then the same amount of energy over a larger volume, right?

Dark energy may be the energy of vacuum itself, that's why it's constant. And no, energy conservation does not apply in this case. There is a good blog article on precisely this question by Sean Carroll: https://www.preposterousuniverse.com/blog/2010/02/22/energy-...

Re: Webb and Hubble confirm Universe's expansion rate

#225

Post by isolli »

[Naive question warning]

What if the cosmological constant (from which, if I understand correctly, the Hubble constant is derived) is not constant? Could a changing comological "constant" explain the discrepancy between the various methods of calculating the Hubble constant?

From Wikipedia [0]: The cosmological constant "was revived and reinterpreted as the energy density of space, or vacuum energy, that arises in quantum mechanics. It is closely associated with the concept of dark energy."

Do vacuum energy and dark energy have to be constant?

[0] https://en.wikipedia.org/wiki/Cosmological_constant

Re: Webb and Hubble confirm Universe's expansion rate

#226

Post by brabel »

arandomusername wrote: post #160
lagrange77 wrote: post #109

Earlier quoted context omitted.

Interesting, thanks! Out of curiosity: Can we actually differentiate between the expansion of space itself and the drifting of objects within it in the same direction?

I think we observed some of the galaxies moving away from us at rates faster than speed of light, multiple times faster, which wouldn't work with objects drifting away if we hold by that speed of light is max speed matter can move at.

That's physically impossible. You can't observe something that's beyond your "light cone", as any galaxy "moving" (it's not really moving, it's the space that's getting expanding) faster than light would be. What you're referring to is the fact that we can confidently predict that galaxies at the edge of the observable universe, which we currently see moving away from us really fast, but as they were in the distant past due to their light taking billions of years to arrive at us, are currently, if we could actually see them where they are right now (again: we can't), "moving" faster than light away from us.

Once a galaxy has moved beyond or "light cone", it's lost forever: you won't see it again even if you try moving towards it at light speed for all eternity.

Re: Webb and Hubble confirm Universe's expansion rate

#227

Post by mr_mitm »

oneshtein wrote: post #180
jMyles wrote: post #173

Earlier quoted context omitted.

> we haven't made any new discoveries in cosmology in the past two decades Is that true? At least for my hobbyist understanding of the progress of cosmology, quite a lot seems to have happened in the past two decades. Confirmation of the Higgs Boson at CERN [0] kept me up all night to watch the press conference; I found it extremely exciting. (Maybe you count this strictly as observational particle physics and not co…

Yes, it's true. Mainstream science refuses to accept anything radically new because of huge baggage. Nobody wants to look stupid, then relearn, recalculate, republish, reteach everything, or lose their tenures, grants, etc. It's why science advances in small incremental steps. AFAIK, there is a team of scientists secretly working on radically new set of theories (I got contact but cannot join because of war).

That notion is ridiculous. Finding something radically new is every scientist's dream. Look at how Einstein is perceived, who arguably found one of the most radically new theories. Nobody thought he looked stupid or lost tenure. No one goes into science hoping to simply confirm what everybody already thought was true.

Re: Webb and Hubble confirm Universe's expansion rate

#228

Post by Scubabear68 »

physicles wrote: post #169

The article mentions the cosmic distance ladder, which is one of my favorite things in all of science. How do we know how far away the really far stuff is? It's non-trivial and I find the history fascinating. It all started with knowing the distance from the earth to the sun. Nobody had a clue until Richer and Cassini got within 10% in 1672. Then we nailed it down in 1769 with James Cook's voyage to Tahiti, the prima…

It is amazing how much of basic science is rooted in simple geometry.

Re: Webb and Hubble confirm Universe's expansion rate

#229

Post by mr_mitm »

willis936 wrote: post #129
pdonis wrote: post #122

Earlier quoted context omitted.

I'm not sure what you mean by "phantoms in the data". The distribution of stress-energy is a free parameter in GR; it has to be inferred from observations. The terms "dark matter" and "dark energy" are just names for, respectively, "stress-energy that acts like the matter we can see, but we can't see it", and "stress-energy that acts like a cosmological constant". Neither of those things poses any problem for GR, sin…

>"Dark matter" poses a problem for particle physicists, who have so far been unable to find any fundamental particles that would produce the observed properties. It's clear to me why we haven't made any new discoveries in cosmology in the past two decades. It's this exact attitude of "the model is the truth". All models are wrong. The data can help you improve it, but you have to at least want to improve it.

The true reason we have made little progress in the past 20 or so years (and a 20 year slouch is historically nothing unusual) is that pretty much all data we collected in that time frame confirmed the standard model. It's the one big dilemma cosmology has. The standard model (LambdaCDM) works unreasonably well. Our problems with it are largely theoretical. New data is also hard to come by. Look at how long it took to plan, build and launch Euclid, cosmology's big hope of finding new physics. The hubble tension from the OP's article is already the most interesting discovery since 1998 when evidence for dark energy was first seen.

And trust me, all scientists know that all models are wrong. This isn't some unique insight that is beholden to amateur scientists on the sidelines.

Re: Webb and Hubble confirm Universe's expansion rate

#230

Post by pigpang »

denton-scratch wrote: post #223
pigpang wrote: post #207

Earlier quoted context omitted.

It's just an interpretation. Your interpretation is similar to the Big Bang model of visible Universe expansion. If you can convince us that your model is better than other models, then we will use your model, but nobody can prove than a model is correct, unless we will find a hidden recorder somewhere which was turned on for few dozens of billion years. Photon will hit something, or will travel until it will be reds…

> (photon is a wave, so it waves something) That sounds suspiciously like postulating the 'ether'. Surely what a photon 'waves' is the electromagnetic field, which is not a medium, and which fills the whole of spacetime. There is no 'end of the medium'.

"Field" means 3d array of numbers. Spacetime means 4d array of numbers. You are talking about mathematical model of Universe, while I'm talking about physics. Mountain is not just an excitement in a height field. If photon is not waving something, then it's not a wave. Physicists prove that photon is a wave.
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