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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

#231

Post by pigpang »

luc4sdreyer wrote: post #221
pigpang wrote: post #193

Earlier quoted context omitted.

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!

I have my own theory, which is not disproved yet: gravitational background noise slow down light a bit. Gravitation affects whole stream of photons in uniform way, not individual photons. Moreover, it doesn't change direction of photons, so no blur or scattering. My napking maths, which I did few months ago, tells that gravitational delaying should case effect of same magnitude as in red shift, (I did calculation for one frequency only, for proper calculation I need to know the temperature of the noise).

Re: Webb and Hubble confirm Universe's expansion rate

#232

Post by cygx »

risfriend wrote: post #219
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…

The distance was also known in 16th century as per Hindu hymn of hanuman chalisa - https://hinduism.stackexchange.com/questions/10370/did-our-a...

Not sure that's convincing: Why would I multiply a unit of time (Yug) with unit of distance (Yojan) to arrive at the distance to the sun? Also note that per Wikipedia, the historical value of the Yogan can range from 3.5km (~2.2 miles) to 15km (~9.3 miles). How was the value of 8 miles chosen?

Re: Webb and Hubble confirm Universe's expansion rate

#233

Post by baq »

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…

space expanding means what it literally says: there is more space everywhere at once. there was less a moment ago and now there's more. the longer the distance, the more space gets added in between, thus the effect is extreme on universe scale and undetectable on planetary scales.

Re: Webb and Hubble confirm Universe's expansion rate

#234

Post by cygx »

digging wrote: post #124
itishappy wrote: post #100

Earlier quoted context omitted.

Doesn't dark energy do exactly that? 70% of the energy of the universe doesn't seem to want to play by our rules!

Yes, but my understanding is that dark energy doesn't play by the same rules, it's an exception. I certainly can't explain why but also it may not be known exactly why, given dark energy is an unexplained phenomenon.

The party line is that energy is not conserved at cosmological scales. However, it's more of a semantic question: We can tell you exactly by how much it gets violated (that's basically the first Friedmann equation), and if you prefer, you can attribute the missing energy to the gravitational field. A lot of physicists don't like that approach as it isn't possible to write down a corresponding stress-energy tensor, ie gravitational energy cannot be properly localized.

Re: Webb and Hubble confirm Universe's expansion rate

#235

Post by whimsicalism »

luc4sdreyer wrote: post #212
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…

> Nobody had a clue In the 3rd century BC, Aristarchus calculated that the Sun was between 18 and 20 times farther away from the Earth than the Moon, and proposed the Heliocentric model as a result. The true value is instead approximately 400 times. But it's incredible given that he didn't have lenses, the value of Pi, and that the Geocentric model was considered correct until 1800 years after his death. https://en.w…

yeah i would call estimating it as 20x when it is actually 400x firmly within “not having a clue”.

He didn’t say nobody had a clue about heliocentrism.

Re: Webb and Hubble confirm Universe's expansion rate

#236

Post by whimsicalism »

risfriend wrote: post #219
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…

The distance was also known in 16th century as per Hindu hymn of hanuman chalisa - https://hinduism.stackexchange.com/questions/10370/did-our-a...

Strongly doubt this

Re: Webb and Hubble confirm Universe's expansion rate

#237

Post by kmm »

isolli wrote: post #225

[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 qu…

The Hubble constant is not necessarily derived from the cosmological constant. To be clear, it's not even a constant either, it's a proportionality factor between the recessional velocity of distant objects and their distance from us. Though in some usages it refers to the value of this factor at the current time, which would in fact make it a constant. Regardless, even without a cosmological constant, after the Big Bang you'd still have an expanding universe, possibly collapsing or endlessly expanding, and I like to think of the Hubble constant/parameter in this case as representing the "momentum" the matter in the universe has left from the Big Bang.

The cosmological constant does in fact have to be constant within the constraints of general relativity. The mathematical machinery of GR only allows two parameters: Newton's constant G, representing the coupling of matter to gravity, and the cosmological constant. Both have to be true constants, numbers with a unit.

However, this is only true of the most basic theory of dark energy, where you directly add a constant to the general relativistic lagrangian. More complicated theories, like, for example, quintessence, involve adding new dynamical fields to the theory. The "effective cosmological constant" associated to such theories, quantifying the effect these fields are having on the expansion of the universe, can dynamically change over time, and some of these theories are proposed to solve the Hubble tension. To be clear, although none of these theories are fringe or pseudoscience, they haven't been accepted as a final explanation either, resolving these issues is still a work in progress, at this point they're all simply interesting hypotheses.

Re: Webb and Hubble confirm Universe's expansion rate

#238

Post by cygx »

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.

This is correct: For example, at time of emission of the light we receive today, GN-z11 had a recession velocity above 4c. A redshift of 1090 (which is the approximate redshift of the cosmic microwave background) corresponds to a recession velocity on the oder of 60c.

Re: Webb and Hubble confirm Universe's expansion rate

#239

Post by cygx »

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…

The Hubble sphere (the place where recession velocities hit the speed of light) is not the same as the particle horizon (our past lightcone at current cosmological time, the boundary of the observable universe) or the cosmic event horizon (our past lightcone at infinite cosmological time, the boundary of the asymptotically observable universe).

Cf the last paragraph of https://en.wikipedia.org/wiki/Hubble_volume

Observations indicate that the expansion of the universe is accelerating, and the Hubble constant is thought to be decreasing. Thus, sources of light outside the Hubble horizon but inside the cosmological event horizon can eventually reach us. A fairly counter-intuitive result is that photons we observe from the first ~5 billion years of the universe come from regions that are, and always have been, receding from us at superluminal speeds.

Re: Webb and Hubble confirm Universe's expansion rate

#240

Post by mr_mitm »

isolli wrote: post #225

[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 qu…

Dark energy is a constant in the standard model (equivalent to the cosmological constant) and all observations I'm aware of besides the Hubble tension are consistent with it being constant. But nothing stops you from going beyond the standard model, and people have done that and proposed models with a dynamic dark energy density, for example quintessence models. They'd solve some theoretical issues with the standard model, but so far no observations have been precise enough to differentiate between those models and the standard model.

Having a dynamic dark energy is a proposed solution to the Hubble tension: https://arxiv.org/abs/2103.01183

That is, besides a whole family of potential other solutions:

Dark energy in extended parameter spaces [289] Early Dark Energy [235] Early Dark Energy [229] Dynamical Dark Energy [309] Phantom Dark Energy [11] Decaying Warm DM [474] Metastable Dark Energy [314] Dynamical Dark Energy [11, 281, 309] Neutrino-DM Interaction [506] PEDE [392, 394] GEDE [397] Interacting dark radiation [517] Elaborated Vacuum Metamorphosis [400–402] Vacuum Metamorphosis [402] Self-Interacting Neutrinos [700, 701] IDE [314, 636, 637, 639, 652, 657, 661–663] IDE [314, 653, 656, 661, 663, 670] IDE [656] Self-interacting sterile neutrinos [711] Critically Emergent Dark Energy [997] Unified Cosmologies [747] Generalized Chaplygin gas model [744] f (T ) gravity [814] Scalar-tensor gravity [856] Galileon gravity [876, 882] ¨Uber-gravity [59] Modified recombination [986] Power Law Inflation [966] Reconstructed PPS [978] Super ΛCDM [1007] f (T ) [818] Coupled Dark Energy [650]

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