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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

#331

Post by tzs »

brabel wrote: post #226
arandomusername wrote: post #160

Earlier quoted context omitted.

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 p…

It's a bit more complicated than that. The PBS Space Time episode "How Much Of The Universe Can Humanity Ever See?" [1] might be interesting to you.

The next episode, "How Far Beyond Earth Could Humanity Spread?" [2] might also be interesting.

[1] https://www.youtube.com/watch?v=eVoh27gJgME

[2] https://www.youtube.com/watch?v=R-eIUxwcQo4

Re: Webb and Hubble confirm Universe's expansion rate

#332

Post by throwawaymaths »

raattgift wrote: post #318
throwawaymaths wrote: post #294

Earlier quoted context omitted.

I am not a physicist, but iirc the idea of the alternative explanation of the CMB is that if you time evolve backwards intergalactic dust over expansion, you reach a point where the dust gets really dense and effectively opaque. So this isn't summing all of the dust you go through, but rather the redshift all the way back to an era when the universe was super dusty (with the expected thermal signature of that era)

Maybe you can dig up a reference, because you're on the verge of telling the conventional cosmology in a time-reversed way. Under time reversal eventually the very first stars disintegrate into mostly atomic hydrogen, which compresses and heats adiabatically. Eventually it becomes hot enough that the hydrogen ionizes. Ignoring processes which alter photon number, the hot nuclei and electrons form a dense fog. As with…

> How do you preserve that density during expansion

You don't. We aren't in a particularly dusty universe right now. It's also not completely clear. There is dust. This dust is dilute. If our universe is expanding, at some point that dust was denser.

Now run the numbers from known estimates of how thinly dusty out universe is now. Given the rate of expansion, You might get a somewhat dusty universe at some time after the big bang, no?

I don't know how to say this in any plainer English. Your comments are full of lots of words that are muddling the point.

> I'm not aware of any published or even serious attempt to do this

That's too bad. I would want to see it done, if only to confirm that the CMB can't be intergalactic dust from a denser era

Re: Webb and Hubble confirm Universe's expansion rate

#333

Post by raattgift »

throwawaymaths wrote: post #332
raattgift wrote: post #318

Earlier quoted context omitted.

Maybe you can dig up a reference, because you're on the verge of telling the conventional cosmology in a time-reversed way. Under time reversal eventually the very first stars disintegrate into mostly atomic hydrogen, which compresses and heats adiabatically. Eventually it becomes hot enough that the hydrogen ionizes. Ignoring processes which alter photon number, the hot nuclei and electrons form a dense fog. As with…

> How do you preserve that density during expansion You don't. We aren't in a particularly dusty universe right now. It's also not completely clear. There is dust. This dust is dilute . If our universe is expanding, at some point that dust was denser. Now run the numbers from known estimates of how thinly dusty out universe is now. Given the rate of expansion, You might get a somewhat dusty universe at some time afte…

> Now run the numbers

Why don't you do that, and share the results here?

> I would want to see it done

Why don't you do it yourself?

Re: Webb and Hubble confirm Universe's expansion rate

#334

Post by beaned »

Vecr wrote: post #267
beaned wrote: post #148

Stupid question: how do we know that the universe is strictly exponentially expanding, and not both expanding and contracting in perpetuity like a sin wave? And could such an idea have anything to do with the Hubble tension?

That's the "big crunch" theory. It's been pretty dubious for quite a while now though.

The "big crunch" wikipedia says that it's an idea about the end of the universe, where expansion will reverse and everything will collapse back in on itself.

That is not what I'm asking. I'm asking if expansion and contraction could fluctuate in perpetuity, like stress waves through a block of jello.

Re: Webb and Hubble confirm Universe's expansion rate

#335

Post by narag »

mr_toad wrote: post #258
narag wrote: post #105

Earlier quoted context omitted.

How do we know that galaxies are accelerating away from us and not moving at constant speed? There's a more basic question: How do we know the galaxies are moving? It seems (I haven't seen any other response, like... ever) that we have one and only one way to measure the speed of galaxies: the red shift. It's impossible to triangulate those huge distances and the time scale would also be a barrier, so no way of confi…

> It's impossible to triangulate those huge distances https://en.wikipedia.org/wiki/Cosmic_distance_ladder

Funny, because that article says exactly the same.

"Short" distances are calculated by parallax, taking Earth's orbit diameter as the base.

From there, it's a extrapolation of the spectrum of known types of objects. Not triangulation. Moreover, IIRC individual stars can't be discerned in other galaxies, even the nearest ones, except maybe supernovas.

So at the distances that red shift manifests, no triangulation, only red shift.

Re: Webb and Hubble confirm Universe's expansion rate

#336

Post by [deleted] »

at_a_remove wrote: post #165
narag wrote: post #105

Earlier quoted context omitted.

How do we know that galaxies are accelerating away from us and not moving at constant speed? There's a more basic question: How do we know the galaxies are moving? It seems (I haven't seen any other response, like... ever) that we have one and only one way to measure the speed of galaxies: the red shift. It's impossible to triangulate those huge distances and the time scale would also be a barrier, so no way of confi…

You're not going to get a simple answer because the answer is quite complex. Astronomy is the paleontology of photons. You should take an astronomy course if you really want to know, but essentially a "ladder" was built of distances, starting with the very near and slowly building outward using various techniques and discoveries of physics as they became available. This is called the cosmic distance ladder . You star…

[deleted]

Re: Webb and Hubble confirm Universe's expansion rate

#337

Post by bryango »

tzs wrote: post #28

A little background based on a few articles about this plus my recollection of PBS Space Time videos on this: There are at least two ways to try to figure out the rate of expansion of the universe (which is called the Hubble Constant). • From variations in the cosmic microwave background (CMB) which are the result of certain conditions in the early universe it is possible to figure out what the expansion rate should…

> They do _not_ resolve the Hubble tension.

Thank you! They should have clarified this up front in the title or the abstract. The original article makes it sound like it has been resolved:

> (title) Webb & Hubble confirm Universe’s expansion rate

> (abstract) ... However, a persistent difference, called the Hubble Tension, is seen between the value of the constant measured with a wide range of independent distance indicators and its value predicted from the afterglow of the Big Bang. The NASA/ESA/CSA James Webb Space Telescope has confirmed that the Hubble Space Telescope’s keen eye was _right all along_ (emphasis mine), erasing any lingering doubt about Hubble’s measurements.

This feels like bad reporting to me. A better title would be "Webb confirms Hubble's measurement of Universe’s expansion rate", but that would probably be less exciting...

Re: Webb and Hubble confirm Universe's expansion rate

#338

Post by [deleted] »

semi-extrinsic wrote: post #187
Sprocklem wrote: post #168

Earlier quoted context omitted.

IIRC, this was one of the explanations proposed when the existence of a red shift was first noted: that the light is somehow slowly losing its energy over very long distances, becoming “redder” as it did so. It ultimately lost out to the dark energy / space-time expansion theory, although I do not recall why. Presumably there was some observation that precluded “degrading” light from being the sole explanation.

There are several challenges for "tired light", or indeed any theory that's an alternative to expansion of the universe. The theory has to explain why the light gets redshifted, but does not get blurred, and the spectral lines do not get broadened. This severely restricts the type of interactions possible. Also the theory has to explain the consistency between redshifts within our own galaxy, to that of far-away gala…

[deleted]

Re: Webb and Hubble confirm Universe's expansion rate

#339

Post by explaininjs »

explaininjs wrote: post #320
denton-scratch wrote: post #303

Earlier quoted context omitted.

> whether there exists an external "system clock" I'll ignore your analogy with a CPU, which I don't think is apposite. Whether there's a 'system clock', a sort of reference clock that can tell you how fast time is passing, so you can calibrate other clocks against it, seems to be the same category error. As far as I can see, either time is all there, all at once; or one second lasts exactly one second. (I've perpetr…

You're certainly welcome to completely ignore the question at hand, it's just surprising that you'd use so many characters to do so. The question is if there's a different sort of thing beyond our idea of time. We have our concept of N caesium oscillations is the base reference for everything, and the duration of all action is derived from it. Could there be more depth to the rate at which things occur than that, esp…

Could those processes, for instance, have configured the initial state of the entire universe in 6 of their days, but 13.8B-6,000 of our call years? I see no reason why not.

Re: Webb and Hubble confirm Universe's expansion rate

#340

Post by throwawaymaths »

raattgift wrote: post #333
throwawaymaths wrote: post #332

Earlier quoted context omitted.

> How do you preserve that density during expansion You don't. We aren't in a particularly dusty universe right now. It's also not completely clear. There is dust. This dust is dilute . If our universe is expanding, at some point that dust was denser. Now run the numbers from known estimates of how thinly dusty out universe is now. Given the rate of expansion, You might get a somewhat dusty universe at some time afte…

> Now run the numbers Why don't you do that, and share the results here? > I would want to see it done Why don't you do it yourself?

Im not a physicist. I am not selling a theory that needs to answer to a simple challenge. Cosmologists are, it is their responsibility. Moreover, if I did, it would be a huge waste of time because dollars to doughnuts I get gatekept and no one believes me, and, if anything it could make challenging the CMB worse because this model gets filed away as "that one crackpot throwawaymaths idea don't listen to it".

Back when I was a hard scientist it was MY responsibility to show that I had done all the controls correctly. And trust me that was hours, weeks of grueling manual labor. A pity if physicists aren't held to the same standard.

Imagine this exchange.

Reviewer: Did you run this control?

Scientist: No, you run it.

Good luck publishing.

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