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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

#131

Post by tsimionescu »

dylan604 wrote: post #106
kloop wrote: post #98

Earlier quoted context omitted.

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.

The point was that science doesn't allow for certainty, by construction. We're not certain the sun will rise tomorrow, we're not certain the speed of light is a limit, we're not certain that F=ma or that E=mc².

Those that want certainty have to look to religion, or to pseudoscience. And they will certainly be wrong.

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

#132

Post by cosmicjoe »

As a non-scientist I've always found the Cosmic Distance Ladder as likely to be inaccurate due its assumption about the constant brightness of Standard Candle stars over their lifetime, and the compounding of error at each rung of the ladder. Direct measurement of the CMB seems to be simpler with less chance of error.

https://en.wikipedia.org/wiki/Cosmic_distance_ladder

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

#133

Post by AutoDunkGPT »

cluckindan wrote: post #66
CamperBob2 wrote: post #47

Earlier quoted context omitted.

"Sorry, but as a large language model, I cannot provide advice on how to reverse entropy."

Thinking… Thinking… Thinking… The word ”entropy” can be reversed by writing its letters in reverse order. E-N-T-R-O-P-Y The first letter is E. The second letter is N. The third letter is T. The fourth letter is R. The fifth letter is O. The sixth letter is P. The seventh letter is Y. Thinking… To construct the reversed word, the seventh letter must be first, and the sixth letter must be second, and the fifth letter m…

bravo, sir

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

#134

Post by cruffle_duffle »

tsimionescu wrote: post #131
dylan604 wrote: post #106

Earlier quoted context omitted.

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.

The point was that science doesn't allow for certainty, by construction. We're not certain the sun will rise tomorrow, we're not certain the speed of light is a limit, we're not certain that F=ma or that E=mc². Those that want certainty have to look to religion, or to pseudoscience. And they will certainly be wrong.

Bingo. People who think science is fact dont understand science.

The actual fact is, we humans really don’t know much about the universe and indeed there may be truths and knowledge that we’ll never know the answer to. Like… why the fuck are we here? Where did all this stuff come from. Sure we have theories and have logical conclusions but at the end of the day… we are tiny and the universe is mind bogglingly huge. It is peak human arrogance to think we truly know anything at all.

It’s very humbling to realise how little we actually know. What we do know… we know. We are masters of electro-magnetism, chemistry, etc… but when it comes to the big questions it’s all a shot in the dark.

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

#135

Post by ridgeguy »

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?

Nope, cosmic Zeno's Paradox. Collapse never quite happens.

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

#136

Post by XorNot »

cosmicjoe wrote: post #132

As a non-scientist I've always found the Cosmic Distance Ladder as likely to be inaccurate due its assumption about the constant brightness of Standard Candle stars over their lifetime, and the compounding of error at each rung of the ladder. Direct measurement of the CMB seems to be simpler with less chance of error. https://en.wikipedia.org/wiki/Cosmic_distance_ladder

Direct measurement of the CMB can also have problems if our assumptions about it are wrong. A major goal of having two methods is that they should coalesce to the same result within margin of error - that they didn't told us we were missing something.

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

#137

Post by jiggawatts »

gorbot wrote: post #123
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…

I'm dumb and barely understand things at a high level, but standard candles never sat right with me so it's interesting to hear that they might not be, but then again who knows.

The idea is that standard candles are based on chemistry and microscopic physics only, not cosmology.

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

#138

Post by antognini »

shomp wrote: post #112
antognini wrote: post #54

Earlier quoted context omitted.

Noether's theorem tells us when we would expect conservation laws to hold and when we would expect them to fail. In the case of global energy conservation, there would have to be a global time invariance associated with the spacetime. But this is manifestly not the case in an expanding universe. It is generally not even possible to have a well defined notion of global energy in a dynamic spacetime.

Noether's theorem tells us when symmetry guarantees conservation, but it says nothing about conservation in the absence of that symmetry - it's not a biconditional statement. Talking about endless expansion is like observing 1 second of a pendulum's swing and concluding there's no time symmetry because it's only moving in one direction. The symmetry exists at the full cycle scale, not the snapshot scale.

It's true that it leaves open the possibility of a conserved quantity that is not associated with a symmetry. But the kinds of conservation laws we are thinking about, like conservation of energy, do originate from a symmetry. So if the symmetry is broken it is very reasonable to assume that the conservation law would be broken as well.

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

#139

Post by jumploops »

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.

“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.

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

#140

Post by JumpCrisscross »

negativelambda wrote: post #116
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 know the team that did this. In fact i was listening to their seminar just a few days ago. They are very careful and have been working on this a long time. One caveat that they readily admit is that the sample used to create the luminosity age relation has some biases such as galaxy type and relatively lower redshift. They will be updating their results with the Rubin LSST data in the next few years. Exciting times…

> after decades of a standard LCDM model

Could you help me understand this sentence: "After correcting for this age bias as a function of redshift, the SN data set aligns more closely with the cold dark matter (CDM) model”?

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