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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

#361

Post by raattgift »

thehappypm wrote: post #345
__turbobrew__ wrote: post #163

Earlier quoted context omitted.

Degrading light sounds like an interesting idea to me, you could call it the “cosmological damper” if you will. Thought experiment: imagine you have light particles in a perfectly circular orbit around a black hole. Does the light ever fall into the black hole or does it orbit for eternity?

Can photons collide? My understanding is they can’t. If they could, Hawking radiation would interfere with the eternal orbit.

> Can photons collide?

Yes, at high energies and with electrons or atomic nuclei nearby.

https://en.wikipedia.org/wiki/Two-photon_physics

> Hawking radiation would interfere with the eternal orbit

For tractability Hawking radiation tends to be studied using a non-interacting scalar field (often massless), rather than the fields of the Standard Model (which are very much interacting, and have a variety of masses).

Hawking started that in his "Black hole explosions?" (1974) which (if you're not allergic to sci-hub) you can read at https://sci-hub.se/https://www.nature.com/articles/248030a0>: "consider (for simplicity) a massless Hermitean scalar field \phi which obeys the covariant wave equation ... in an asymptotically flat space time containing a star which collapses to produce a black hole.". In the short paper, he's very much not considering photons or pions, and really doesn't need to in order to make his point.

The thermal spectrum of a real black hole will be in all the Standard Model fields, and except very late in the eventual evaporation will be dominated by very low energy photons originating at a fair distance outside the event horizon.

What do you mean by "eternal orbit"?

Real black holes do not extend to the infinite past. If a black hole ultimately Hawking-evaporates, in finite time there's nothing left to orbit. Late in the evaporation, there will also be a lot of very high energy gamma rays and heavier particles excited in their respective quantum fields of the Standard Model. These will all tend to participate in high-energy multi-particle interactions rather more complicatedly than the end result of Hawking's 1974 description.

Re: Webb and Hubble confirm Universe's expansion rate

#362

Post by raattgift »

__turbobrew__ wrote: post #163
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…

Degrading light sounds like an interesting idea to me, you could call it the “cosmological damper” if you will. Thought experiment: imagine you have light particles in a perfectly circular orbit around a black hole. Does the light ever fall into the black hole or does it orbit for eternity?

Many black hole solutions of the Einstein Field Equations of General Relativity admit a photon sphere or equivalent(s) where light can orbit the black hole, but not usually stably, and in physically reasonable black hole solutions there is no stable circular orbit for light at all, so no eternal orbit. (The orbit can be quite long on human scales though, before the light eventually leaves the area around the black hole, or spirals into the black hole).

As a first step, you could can check out https://en.wikipedia.org/wiki/Photon_sphere> and https://en.wikipedia.org/wiki/Innermost_stable_circular_orbi...>

Re: Webb and Hubble confirm Universe's expansion rate

#363

Post by explaininjs »

denton-scratch wrote: post #342
explaininjs wrote: post #320

Earlier quoted context omitted.

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…

> You're certainly welcome to completely ignore the question at hand What I ignored was an analogy. Not an argument from analogy; and not a question. Just a rhetorical device, which I considered irrelevant, and didn't feel like arguing about. > the base reference for everything Caesium oscillations are a proxy for the passage of time. I can imagine a universe in which the rate of Caesium oscillations might vary, or b…

I mentioned a practical implication for interacting timescales in the sibling comment.

Re: Webb and Hubble confirm Universe's expansion rate

#364

Post by miramba »

Vecr wrote: post #269
miramba wrote: post #265

Earlier quoted context omitted.

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.

Indeed. But keyword is „inferred“, assuming that all laws worked the same at any point in a gigantic timeframe, at any point in a gigantic universe. Except singularities. And quantum mechanics as it seems? And maybe dark energy. Oh and lately, maybe gravity waves. Btw I was once in a lecture room in Berlin where they claimed that one of the thermodynamic laws where discovered…while giving a lecture. Not too long ago, perhaps 150-200 years. Doesn‘t seem so unlikely that somebody comes up with a new version at some point.

Re: Webb and Hubble confirm Universe's expansion rate

#365

Post by miramba »

mr_mitm wrote: post #315
miramba wrote: post #265

Earlier quoted context omitted.

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."

We can literally see into the past 13 billion years ago by building space crafts that collect microwave radiation, because we aren't as primitive as you may want us to believe.

No, not literally…presumably. You believe that the radiation you look at is that old, because you measure certain wavelengths and study ladders, but you can‘t really prove it. Proving that something is 13 billion years old is beyond the capabilities of us apes, at least at this point.

Re: Webb and Hubble confirm Universe's expansion rate

#366

Post by mr_mitm »

miramba wrote: post #365
mr_mitm wrote: post #315

Earlier quoted context omitted.

We can literally see into the past 13 billion years ago by building space crafts that collect microwave radiation, because we aren't as primitive as you may want us to believe.

No, not literally…presumably. You believe that the radiation you look at is that old, because you measure certain wavelengths and study ladders, but you can‘t really prove it. Proving that something is 13 billion years old is beyond the capabilities of us apes, at least at this point.

Can you really prove anything beyond your own existence? Descartes says no. Maybe all your senses are just an illusion.

Re: Webb and Hubble confirm Universe's expansion rate

#367

Post by throwawaymaths »

raattgift wrote: post #358
throwawaymaths wrote: post #340

Earlier quoted context omitted.

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 whe…

True; people with any sort of expertise will be less generous with their attention if it's clear that you won't make an effort to understand what it is you're challenging. Additionally, is it really you that's mounting a challenge? Quoting you: "There's a 'fringe' theory ... the primary proponent ... if my understanding is correct it would still be compatible with ..." https://news.ycombinator.com/item?id=39674424 >.…

What you were doing was muddling the point. As best I can tell (and it was difficult to understand what you were saying), you were talking about summing blackbody radiation over time and distance. That's not what this model is.

Re: Webb and Hubble confirm Universe's expansion rate

#368

Post by DrFalkyn »

munksbeer wrote: post #297
tvshtr wrote: post #264

Earlier quoted context omitted.

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.

I understand that concept. I'm asking, how can you materially tell the difference?

I think it has to do with the observation that no matter in which directinn we look, galaxies are moving away. Its not like we look towards one direction and say, "aha, that must be the center of the universe". Its the same story in ALL directions - we wee galaxies moving away from us at increasing velocity.

Re: Webb and Hubble confirm Universe's expansion rate

#369

Post by DrFalkyn »

miramba wrote: post #365
mr_mitm wrote: post #315

Earlier quoted context omitted.

We can literally see into the past 13 billion years ago by building space crafts that collect microwave radiation, because we aren't as primitive as you may want us to believe.

No, not literally…presumably. You believe that the radiation you look at is that old, because you measure certain wavelengths and study ladders, but you can‘t really prove it. Proving that something is 13 billion years old is beyond the capabilities of us apes, at least at this point.

We know that light has a finite speed. We've measured it.

We know that speed is independent of the relative velocities between the litter and the observer. Again, we've carried out experiments and measured that as well

Re: Webb and Hubble confirm Universe's expansion rate

#370

Post by mberger »

raattgift wrote: post #360
mberger wrote: post #357

Earlier quoted context omitted.

I've wondered: Do we know that the balloon has always been inflating at the same rate? Do we know if the dimples on the balloon expand as fast as the rest of it? Do the areas around the dimples expand faster?

I'll get to your questions below. If you want any of the preliminaries or the non-tl;dr answers explained a bit more simply, say so in a reply and I'll do my best in response. Your questions (if you pardon the expression) poke holes in the balloon analogy. The latex or other stretchy balloon material is denser and under less tension around dimples. Local experiments by a (spatially) 2d observer could determine these…

I am not a physicist or cosmologist so i won't pretend to understand all of your answers but this has given me a great starting point to learn more and i greatly appreciate you taking the time to write it. I had a pretty theory that we were seeing galaxies accelerate away from each other due to the rate of expansion being greater outside of gravity wells. I will reread your answer a couple of times until i get off there is any support for it but my initial reading suggests it's up there with light needing a medium to travel.
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