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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

#181

Post by throwaway-0001 »

the__alchemist wrote: post #179
JumpCrisscross wrote: post #84

“Supernova (SN) cosmology is based on the key assumption that the luminosity standardization process of Type Ia SNe remains invariant with progenitor age. However, direct and extensive age measurements of SN host galaxies reveal a significant (5.5σ) correlation between standardized SN magnitude and progenitor age, which is expected to introduce a serious systematic bias with redshift in SN cosmology. This systematic…

I did a deep dive into cosmology simulations ~a year ago. It was striking how much is extrapolated from the brightness of small numbers of galaxy-surface pixels. I was looking at this for galaxies and stars, and observed something similar. The cosmology models are doing their best with sparse info, but to me it seemed that the predictions about things like Dark Matter and Dark Energy are presented in a way that's too…

Yeah a lot of stuff seems to be based on these fuzzy data which I also think is unreliable.

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

#182

Post by mr_mitm »

the__alchemist wrote: post #179
JumpCrisscross wrote: post #84

“Supernova (SN) cosmology is based on the key assumption that the luminosity standardization process of Type Ia SNe remains invariant with progenitor age. However, direct and extensive age measurements of SN host galaxies reveal a significant (5.5σ) correlation between standardized SN magnitude and progenitor age, which is expected to introduce a serious systematic bias with redshift in SN cosmology. This systematic…

I did a deep dive into cosmology simulations ~a year ago. It was striking how much is extrapolated from the brightness of small numbers of galaxy-surface pixels. I was looking at this for galaxies and stars, and observed something similar. The cosmology models are doing their best with sparse info, but to me it seemed that the predictions about things like Dark Matter and Dark Energy are presented in a way that's too…

That fuzziness can be quantified. It's called error bars. Whenever physicists perform a measurement, they always derive a confidence interval from the instruments they use. They take great care of accounting for the limits of each individual instrument, perform error propagation and report the uncertainty of the final result.

Consider figure 5 of the following article for example:

https://arxiv.org/abs/1105.3470

The differently shaded ellipses represent different confidence levels. For the largest ellipsis, the probability of the true values being outside of it is less than 1%. We call that 3-sigma confidence.

> Whenever I read things like "This model can't explain the bullet cluster, or X rotation curve, so it's probably wrong" my internal response is "Your underlying data sources are too fuzzy to make your model the baseline!"

Well, then do some error analysis and report your results. Give us sigmas, percentages, probabilities. Science isn't based on gut feelings, but cold hard numbers.

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

#183

Post by mr_mitm »

wtcactus wrote: post #173
jumploops wrote: post #139

Earlier quoted context omitted.

“We can’t observe the whole universe, so cosmology is not really about the universe. It’s about the observable patch and the assumptions we make about the rest.” (paraphrasing George Ellis) We’re in a bounding sphere, with a radius that’s roughly 46.5 billion lightyears, so any observation we make may be true for our local observable range, but there’s no (known) way to know what’s beyond that sphere.

Right, but everywhere we look the universe is roughly the same at same distances, so it’s acceptable to extrapolate.

Even if not, it's still worthwhile to explore everything as far as we can see.

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

#184

Post by the__alchemist »

mr_mitm wrote: post #182
the__alchemist wrote: post #179

Earlier quoted context omitted.

I did a deep dive into cosmology simulations ~a year ago. It was striking how much is extrapolated from the brightness of small numbers of galaxy-surface pixels. I was looking at this for galaxies and stars, and observed something similar. The cosmology models are doing their best with sparse info, but to me it seemed that the predictions about things like Dark Matter and Dark Energy are presented in a way that's too…

That fuzziness can be quantified. It's called error bars. Whenever physicists perform a measurement, they always derive a confidence interval from the instruments they use. They take great care of accounting for the limits of each individual instrument, perform error propagation and report the uncertainty of the final result. Consider figure 5 of the following article for example: https://arxiv.org/abs/1105.3470 The…

On the todo list! Not enough bandwidth, but hoping to get to that in the next year. Great point.

edit: That 1% figure doesn't sound possible unless it has its own set of assumptions that need a confidence!

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

#185

Post by wtcactus »

mr_mitm wrote: post #183
wtcactus wrote: post #173

Earlier quoted context omitted.

Right, but everywhere we look the universe is roughly the same at same distances, so it’s acceptable to extrapolate.

Even if not, it's still worthwhile to explore everything as far as we can see.

Relativity restricts us to explore a very tiny sliver of the universe. We can observe, but we will never be able to interact unless Relativity is completely wrong.

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

#186

Post by shadowgovt »

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.

Oh, I'm not going to care about visitable volume.

With 5 gigayears to work with I'm going to move a few star systems over, break down all the matter orbiting the star into a Dyson sphere made of computronium, and simulate visiting any world I could possibly ever want to.

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

#187

Post by kulahan »

ChrisMarshallNY wrote: post #161
negativelambda wrote: post #124

Earlier quoted context omitted.

Its not publicly available. Maybe for the best haha. The speaker at some point went on a bit of a tirade against many people in the supernovae cosmology community. I think he endured many years of being ignored or belittled.

Did he yell "They LAUGHED at me at Heidelberg! They said I was mad. MAD!" ? It is a very fundamental shift, though. The whole "Dark Energy/Matter" hypothesis has always seemed to me, to be a bit of a "Here, there be dragonnes" kind of thing, but I am nowhere near the level of these folks, so I have always assumed they know a lot that I don't.

It is, but that’s also kinda the point. It’s just a variable to stand in for “whatever tf mass we’ve been missing this whole time” or what-have-you.

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

#188

Post by djeastm »

antonvs wrote: post #40
aatd86 wrote: post #29

I would not be surprised if the universe was somewhat elastic, expands and then contracts and then expands ad infinitam. After all, existence in itself is irrefutable and cannot not exist by definition. If we subscribe to a theory of the multiverse, set theory, likelihood, and interaction driven evolution based on gradient type of fundamental laws. Locally changing. Obviously everything sharing a fundamental quality…

> After all, existence in itself is irrefutable and cannot not exist by definition. I can say the same about forgnoz, which is something I've just invented that must exist by definition. You'd need to try a bit harder to make existence actually inevitable.

All glory to forgnoz, a thing which I assure you does exist!

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

#189

Post by antonvs »

aatd86 wrote: post #159
antonvs wrote: post #99

Earlier quoted context omitted.

> I think they mean existence in general, not the existence of any specific thing. Yes, but the definition of "existence" doesn't require that anything must actually exist. In other words, it is not the case that existence "cannot not exist by definition." > Meaning that if there were no “existence” then we wouldn’t be here to consider its nonexistence. That's an anthropic principle argument, which is not an argument…

Yes but then there is always something that must exist which is the concept of absence of existence. So it doesn't make sense.

That's a requirement that you're imposing. If nothing exists, no concept of absence of existence exists. Concepts are for humans.

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

#190

Post by antonvs »

aatd86 wrote: post #158
antonvs wrote: post #40

Earlier quoted context omitted.

> After all, existence in itself is irrefutable and cannot not exist by definition. I can say the same about forgnoz, which is something I've just invented that must exist by definition. You'd need to try a bit harder to make existence actually inevitable.

You have a material view of existence perhaps. How would the notion of nothingness even exist if there was no existence in the first place? And if we even accepted that nothing was possible, which in itself doesn't make any sense, how would something even start to exist? Well the contradiction is already in the fact that there is a preexisting concept of nothing in the first place. Existence is impredicative too. It…

> How would the notion of nothingness even exist if there was no existence in the first place?

It wouldn't, that's the point. The is no need for a "notion of nothingness" if nothing exists.

Why do you think nothingness doesnt't make any sense? It's a simple concept: no space, no time, and therefore nothing else such as matter, etc.

> how would something even start to exist?

Perhaps it wouldn't. We weren't talking about the origin of the universe from nothing. If you want to say existence is irrefutable because we observe it, that's fine. But it's not irrefutable because of its definition, that's religious circular logic, like the ontological argument.

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