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Analysis indicates that the universe’s expansion is not accelerating

ras.ac.uk

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Re: Analysis indicates that the universe’s expansion is not accelerating

#101

Post by stronglikedan »

nabakin wrote: post #32

> type Ia supernovae, long regarded as the universe’s "standard candles", are in fact strongly affected by the age of their progenitor stars. A key point in the article. From what I understand, this is the main way we measure things of vast distance and, from that, determine the universe's rate of expansion. If our understanding of these supernovae is wrong, as this paper claims, that would be a massive scientific br…

> If our understanding of these supernovae is wrong, as this paper claims, that would be a massive scientific breakthrough.

Indeed. It's so hard to definitively prove things that are, that the most significant breakthroughs prove things that aren't (so to speak), imho.

Re: Analysis indicates that the universe’s expansion is not accelerating

#102

Post by jldl805 »

wtcactus wrote: post #69

Standard candles (all these measurements of redshift according to distance, need us to actually get the distance of what we are measuring right) are the gift that keeps on giving. This study (and many others, depending on the cosmic scales they use) mainly use Supernovas of Type Ia. I.e. the energy emitted by the supernova of a binary acreccion star, which is a star that is capturing the mass from another start that…

>I'm a bit skeptic

Out of curiosity, what data are you drawing or what qualifications do you have that support your skepticism over three different modes of analysis (as well as pretty much every recent development in the field) supporting this claim:

       "Remarkably, this agrees with what is independently predicted from BAO-only or BAO+CMB analyses, though this fact has received little attention so far.""

Re: Analysis indicates that the universe’s expansion is not accelerating

#103

Post by shomp »

ASalazarMX wrote: post #70
shomp wrote: post #51

Mainstream physics has been delighted to ignore/abandon essential conservation laws when talking about the expanding universe. It's kinda weird, I tried publishing a paper on it recently and it was not received well. In general, if conservation laws are to hold, expansion must be balanced with [eventual] contraction, is that not obvious? Apparently it was quite contentious to say until... this article?

> In general, if conservation laws are to hold, expansion must be balanced with [eventual] contraction, is that not obvious? Why would this be? The only physics we know is the one inside our observable universe, there could be variations beyond, or even unknowable laws that don't require conservation of matter outside the edge of the universe. Our incredibly vast universe could be a minuscule blob feeding from an inc…

Because energy cannot be created nor destroyed

Re: Analysis indicates that the universe’s expansion is not accelerating

#104

Post by glenstein »

mrguyorama wrote: post #85
skissane wrote: post #49

Earlier quoted context omitted.

I guess the question is… we know what our current propulsion technology is capable of… given a million years of further technological development, where will our technology be? The idea that, given a million years of further technological development , intergalactic travel might actually be feasible, isn’t really that implausible. Far from certain, but far from implausible either. And that’s the thing-a million years…

Any form of propulsion that obeys Newton has hard limits to it's space travel potential. Even spitting out single particles at near the speed of light for the most efficient way to generate thrust per unit of expelled mass still constrains you to the tyranny of the rocket equation, which puts hard physical limits on you. https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation The rocket equation also underestimates…

Lots of great points here, but I think there's a bit more cause for optimism. For one, generation ships I think are the long-term project for space travel that successfully gets humans somewhere. No easy feat by any means in terms of time, engineering, and risk, but not running up against a wall of physical impossibility.

And nuclear physics is still a wide open frontier. We don't yet have fusion, and there's a lot we don't yet know about quark and gluon plasma and nuclear behavior on astrophysical scales. And if we're talking about technological possibilities against time scales of forever, there's lots of interesting electromagnetic possibilities in the context of superconductivity and metamaterials that we haven't yet exploited and I'm probably not even beginning to do justice to it in its totality as an open ended frontier full of fertile (e.g. vacuum polarization is a poorly understood frontier that might turn out to have interestingly exploitable properties).

You did a great job outlining some devastatingly serious physical limits but I think, again against the timeline of forever, you may be perhaps underselling the possibilities of important and newly exploitable properties of electromagnetism and the nuclear force being brought into application.

Re: Analysis indicates that the universe’s expansion is not accelerating

#105

Post by mabster »

ertgbnm wrote: post #28

Seems like the problem should be pretty easy to figure out. Just need to wait ~5 gigayears and see which model is right. I'm personally hoping for deceleration so that we have more total visitable volume. I'll set a reminder to check back at that time to see who was right.

I just pictured someone getting a message to check which model was right from an ancestor 20 giga generations ago!

Re: Analysis indicates that the universe’s expansion is not accelerating

#106

Post by dylan604 »

kloop wrote: post #98
dylan604 wrote: post #92

Earlier quoted context omitted.

just because you tell me water is not wet does not make it dry. also, the cool thing "about science is it doesn't need you to believe in it" or however the quote goes

Sure, but they didn't say correctness, they said certainty

There are people certain the earth is flat, the moon landings were fake. That certainty doesn't impress me. So I'm just really not sure what the point is.

Re: Analysis indicates that the universe’s expansion is not accelerating

#107

Post by antonvs »

pdonis wrote: post #42
jimbo808 wrote: post #15

Anyone know how credible this is? If true, then that means the big bounce is back on the menu, and the universe could actually be an infinitely oscillating system.

> Anyone know how credible this is? AFAIK the previous models that all assumed that Type 1a supernovae were not affected by the age of the progenitor stars had no actual analysis to back that up; it was just the simplest assumption. This research is now actually doing the analysis.

> AFAIK the previous models that all assumed that Type 1a supernovae were not affected by the age of the progenitor stars had no actual analysis to back that up; it was just the simplest assumption.

Why would you assume this? It's not correct.

Type 1a supernovae aren't even assumed to be "standard candles" as is often claimed: rather, they're standardizable, i.e. with cross-checks and statistical analysis, they can be used as an important part of a cosmological distance ladder.

A great deal of analysis has gone into the development of that distance ladder, with cross-checks being used wherever it's possible to use them.

They look at surface brightness fluctuations in the same galaxies, Tully-Fisher distances[1], tip of the red giant branch distances[2], and even baryon acoustic oscillations[3]

Is it possible that this one single paper has upended all that? Theoretically. Is it likely? No.

[1] https://en.wikipedia.org/wiki/Tully%E2%80%93Fisher_relation

[2] https://en.wikipedia.org/wiki/Tip_of_the_red-giant_branch

[3] https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations

Re: Analysis indicates that the universe’s expansion is not accelerating

#108

Post by cwillu »

Erem wrote: post #79
pdonis wrote: post #37

Earlier quoted context omitted.

> If true, then that means the big bounce is back on the menu I don't think so. Deceleration does not imply recollapse. AFAIK none of this changes the basic fact that there isn't enough matter in the universe to cause it to recollapse. The expansion will just decelerate forever, never quite stopping.

Wait but decelerating forever does in fact imply recollapse doesn't it?

An object on an escape trajectory from another mass is forever decelerating, but it still escapes.

Re: Analysis indicates that the universe’s expansion is not accelerating

#109

Post by channeleaton »

mabster wrote: post #105
ertgbnm wrote: post #28

Seems like the problem should be pretty easy to figure out. Just need to wait ~5 gigayears and see which model is right. I'm personally hoping for deceleration so that we have more total visitable volume. I'll set a reminder to check back at that time to see who was right.

I just pictured someone getting a message to check which model was right from an ancestor 20 giga generations ago!

!remindme 20,000,000,000 years

Re: Analysis indicates that the universe’s expansion is not accelerating

#110

Post by pdonis »

antonvs wrote: post #107
pdonis wrote: post #42

Earlier quoted context omitted.

> Anyone know how credible this is? AFAIK the previous models that all assumed that Type 1a supernovae were not affected by the age of the progenitor stars had no actual analysis to back that up; it was just the simplest assumption. This research is now actually doing the analysis.

> AFAIK the previous models that all assumed that Type 1a supernovae were not affected by the age of the progenitor stars had no actual analysis to back that up; it was just the simplest assumption. Why would you assume this? It's not correct. Type 1a supernovae aren't even assumed to be "standard candles" as is often claimed: rather, they're standardizable, i.e. with cross-checks and statistical analysis, they can b…

> Why would you assume this? It's not correct.

None of your references contradict it, as far as I can see. I'm well aware that Type 1a supernovae are only part of the overall picture, but that observation doesn't contradict what I said.

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