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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

#261

Post by CuriouslyC »

kaashif wrote: post #142
CuriouslyC wrote: post #88

Earlier quoted context omitted.

I think the truth is likely that we live in a very complex universe that can be approximated by these sweeping laws in general, but is very "messy" close up. Consider that while the universe roughly obeys probabilities, it also has will and intent (to a degree we can debate in another conversation).

What do you mean by will and intent? I guess if humans have will and are part of the universe, then the universe has it too, but I don't think that's what you meant.

Hopefully we can agree that at least part of the universe "chooses" outcomes, rather than them occurring randomly. You could assume that "choosing" is what random outcomes feel like but I don't think that's productive.

Given that we have evidence of physical systems evolving their states by conscious choice, that begs the question "Why would large, complex physical systems have a governing force that doesn't exist in smaller physical systems?" Occam's Razor suggests that consciousness and will drive the evolution of all physical systems, and our elegant equations are merely statistical approximations following the law of large numbers given a population with a natural variance. Of course we can debate what it means for a low information system to be conscious and have will, but I think that's a more meaningful debate than trying to pinpoint the exact moment that a system becomes complex enough for the magical emergence fairy to sprinkle consciousness dust on inert matter.

Re: Webb and Hubble confirm Universe's expansion rate

#262

Post by kovacs_x »

I'm 1000% sure, in 20, 50, 100, 500 years humans will look back on "science of 20/21th century" as we look now on say 16/17th century- there were some things that were "mostly" right, but most of it was incorrect / inprecise / incomplete and was a fantasy of earlier thought up models.

It's been like that always. Don't think it'll be different this time. Though people of every time thought they had (almost) complete understanding of the universe. I remember reading that at the beginning of 20th century science was largerly considered complete... we know how it turned out! (think relativity, quantum physics, etc.)

Think about that!

(ps. me personally I just cannot stomach that universe is only <15B "years" old. Not saying there was no BANG! (ie. large cosmic event) back then and we're products of it :), but don't think it was "the beginning of everything". Seems very much like "god created universe!" type of thinking)

Re: Webb and Hubble confirm Universe's expansion rate

#263

Post by Vecr »

kovacs_x wrote: post #262

I'm 1000% sure, in 20, 50, 100, 500 years humans will look back on "science of 20/21th century" as we look now on say 16/17th century- there were some things that were "mostly" right, but most of it was incorrect / inprecise / incomplete and was a fantasy of earlier thought up models. It's been like that always. Don't think it'll be different this time. Though people of every time thought they had (almost) complete u…

Why? Sure, maybe a better number to give is "somewhere around 20", but it's difficult to tell how the "true number" could be over 100 or even 50.

Re: Webb and Hubble confirm Universe's expansion rate

#264

Post by tvshtr »

munksbeer wrote: post #220
EnterpriseTell wrote: post #126

Earlier quoted context omitted.

>In short, even if galaxies weren't accelerating -Galaxies are not accelerating, space is expanding. > Imagine there are some objects in space all moving in random directions and speeds, relative to Earth... -No, In your scenario then end result would be a most static average distance between all objects in the universe. As an infinite number of objects come from infinite distances, there would ALWAYS be objects in t…

What does "space is expanding" mean? That the distance between objects is increasing? How can you tell the difference between "space expanding" and "objects moving in a non-expanding space"? Is there any way to tell the difference or is it just that all objects are moving away at the exact speeds that satisfies the "space expanding" explanation and nothing else? But then, I'm back to what does "space is expanding" me…

Imagine a deflated baloon with two dots drawn close to each other. Now inflate it; the dots didn't move but the plane that they were drawn/positioned on did.

Re: Webb and Hubble confirm Universe's expansion rate

#265

Post by miramba »

Vecr wrote: post #263
kovacs_x wrote: post #262

I'm 1000% sure, in 20, 50, 100, 500 years humans will look back on "science of 20/21th century" as we look now on say 16/17th century- there were some things that were "mostly" right, but most of it was incorrect / inprecise / incomplete and was a fantasy of earlier thought up models. It's been like that always. Don't think it'll be different this time. Though people of every time thought they had (almost) complete u…

Why? Sure, maybe a better number to give is "somewhere around 20", but it's difficult to tell how the "true number" could be over 100 or even 50.

Explanation needed. How can you, a primitive ape on a tiny remote planet with an average lifespan of 80 years (not meant as an insult, I am too), be sure about what happened 15, 20 or 100 BILLION years ago? I think this is what parent meant with: "people of every time thought they had (almost) complete understanding of the universe." - "Don't think it'll be different this time."

Re: Webb and Hubble confirm Universe's expansion rate

#266

Post by rthnbgrredf »

arbitrage wrote: post #93
westurner wrote: post #18

Hubble's law: https://en.wikipedia.org/wiki/Hubble%27s_law Expansion of the universe: https://en.wikipedia.org/wiki/Expansion_of_the_universe : > While objects cannot move faster than light, this limitation only applies with respect to local reference frames and does not limit the recession rates of cosmologically distant objects Given that v is velocity in the opposite direction, and c is the constant reference fram…

Tachyons aren't a thing. Tachyons are sci-fi nonsense. Nothing in the universe can travel faster than the speed of light. This does not hold for the universe itself. It can and does expand faster than the speed of light, using specific reference frames (i.e., big enough). So, space can increase FTL. Particles do not travel faster than light tho, that is nonsense.

Well, we have (virtual) particles that can travel backwards in time, without breaking causality. There's no proof that Tachyons exist, they are purely hypothetical, but they are not outright nonsense.

Re: Webb and Hubble confirm Universe's expansion rate

#267

Post by Vecr »

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.

Re: Webb and Hubble confirm Universe's expansion rate

#268

Post by raattgift »

sebzim4500 wrote: post #250
throwawaymaths wrote: post #104

Earlier quoted context omitted.

No. According to the standard big bang theory the CMB should look like black body radiation. As for smearing, IIRC black body curve has the central limit property

> According to the standard big bang theory the CMB should look like black body radiation. Yes, that's my point. >As for smearing, IIRC black body curve has the central limit property Surely that can only be true for a very specific distribution of temperatures? To go to an extreme, if you combine the spectrum of two objects of different temperatures you do not get anything like a black body curve.

I agree with you; you can't build up a perfect blackbody spectrum by superposing different near-blackbody spectra, and that led to the cosmological thermalization problem. Furthermore, baryonic intergalactic dust isn't like dark matter: we see redshifted spectral features of components of such dusts imprinted on all sorts of backgrounds from quasars to the CMB. The dusts tend to be greybodies. (I'm ignoring the warm-hot intergalactic medium here).

The CMB has narrow spectral lines imposed on it by galaxies, dust clouds, and similar objects. Those lines can be used to measure the CMB effective temperature at an object's redshift. A specific example of how this works is linked at the bottom of this comment. If a similar highly dusty object is found in the foreground of a bright quasar (merely nearby quasars were used in the case below), we could get an even tighter measurement of the CMB effective temperature at the dust, and perhaps look in new ways at how the CMB deviated (at the dusty object) very slightly from a blackbody spectrum. This amounts to a new line of evidence in the study of the expansion history.

More generally, constraining the evolution of the CMB temperature in the matter-dominated era (T_cmb > 4 K, z > ~ 0.4) will prove fatal to ideas like some in this thread (which is already in trouble because of other spectroscopy e.g. the Lyman-alpha forest and Gunn-Peterson trough).

I don't really understand the summary of the "'fringe' theory" at the top of the thread (and I can't identify which specific theory throwawaymaths means). I guess the idea could be that some unknown mechanism might homogenize the emissive components of baryonic intergalactic dust but not circumgalactic medium spectral features. I suppose one could try to investigate a non-adiabatic expansion to explain those features found in the CMB in a nonstandard way. Non-adiabatic components in the expansion have been examined by various theoretical teams in the context of quantum cosmology and/or "fifth force" dark energy, although mostly at much larger lookback times than the the standard surface of last scattering.

I don't understand what was meant by '"longer" (aka galactic expansion) timeframe'.

Finally, "echo of the big bang" isn't really helpful in understanding the origin of the CMB photons, why they're now filling space with a thermal Planck spectrum, and why we detect small variations in that spectrum in narrow views along different directions, but like "fabric of spacetime" I guess we're kinda stuck with the expression.

- --

(Open Access) Riechers, D.A., Weiss, A., Walter, F. et al. Microwave background temperature at a redshift of 6.34 from H2O absorption. Nature 602, 58–62 (2022). https://doi.org/10.1038/s41586-021-04294-5

Re: Webb and Hubble confirm Universe's expansion rate

#269

Post by Vecr »

miramba wrote: post #265
Vecr wrote: post #263

Earlier quoted context omitted.

Why? Sure, maybe a better number to give is "somewhere around 20", but it's difficult to tell how the "true number" could be over 100 or even 50.

Explanation needed. How can you, a primitive ape on a tiny remote planet with an average lifespan of 80 years (not meant as an insult, I am too), be sure about what happened 15, 20 or 100 BILLION years ago? I think this is what parent meant with: "people of every time thought they had (almost) complete understanding of the universe." - "Don't think it'll be different this time."

There's good evidence for it, inferred temperature of the early universe included. Obviously not perfect evidence, but even if you assume "tired light", it's another thing all together to come up with a new version of thermodynamics.

Re: Webb and Hubble confirm Universe's expansion rate

#270

Post by mrguyorama »

dvsfish wrote: post #157
dmd wrote: post #133

Earlier quoted context omitted.

[flagged]

While its probably totally wrong, I think your tone and general attitude to people throwing around imaginative and creative ideas is extremely unproductive and frankly rude. If you want to stifle creative discussions, this is exactly how you'd do it. I found the post to be very stimulating regardless of its validity. And it's not like they're trying to spread it as gospel. There was a lot of disclaimer.

If you want creativity, take an art class. This is cosmology, ostensibly a science. Pulling wild ideas out of thin air and basically ad-libbing a "theory" is not.
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