Dark energy might not be constant after all
First results from the Dark Energy Spectroscopic Instrument offer hints of new physics.
https://arstechnica.com/science/2024/04/dark-energy-might-not-be-constant-after-all/

On 05/04/2024 06:17, Jan Panteltje wrote:
> Dark energy might not be constant after all
> First results from the Dark Energy Spectroscopic Instrument offer hints of new physics.
> https://arstechnica.com/science/2024/04/dark-energy-might-not-be-constant-after-all/

"Dark energy" is the constant that Einstein had to introduce into his
equations for the Universe to make a "Steady State Universe" model work.

The default solution to Einstein-Lemaitre was an exponentially expanding
one which he didn't much like. He described it as his greatest mistake
since reality was much more like his original equation solution as
Hubble later proved by observation.

It is ironic that with improved observational data the same constant now
seems to be making the universe fly apart at beyond exponential rate.
I'm no great fan of "dark energy" but I am told by my friends still in
the field that it is the least worst option now.

It means matter and radiation in the universe will eventually become
very very thin indeed as spacetime rips apart ever more rapidly with time.

TBH I'd prefer there to be something wrong with the Type Ia supernovae
standard candles in the early universe (making them overly bright).

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

I understand that possibility has been ruled out but I don't know any
more details. They are very handy since when they go off they can
outshine an entire galaxy and are visible over huge distances.

You can measure the light curve and determine absolute brightness from
it provided that you catch it early. Amateur astronomers help the
professionals by monitoring galaxies and reporting events in realtime.

Pro scopes only divert to look at them if there is something to see.
(although there are some professional supernova systems as well)

The idea that the fundamental constants of nature might not be quite
constant dates back to Dirac who was the first to make that conjecture.

--
Martin Brown

On a sunny day (Fri, 5 Apr 2024 09:17:23 +0100) it happened Martin Brown
<'''newspam'''@nonad.co.uk> wrote in <uuoc2m$18vkc$1@dont-email.me>:

>On 05/04/2024 06:17, Jan Panteltje wrote:
>> Dark energy might not be constant after all
>> First results from the Dark Energy Spectroscopic Instrument offer hints of new physics.
>> https://arstechnica.com/science/2024/04/dark-energy-might-not-be-constant-after-all/
>
>"Dark energy" is the constant that Einstein had to introduce into his
>equations for the Universe to make a "Steady State Universe" model work.
>
>The default solution to Einstein-Lemaitre was an exponentially expanding
>one which he didn't much like. He described it as his greatest mistake
>since reality was much more like his original equation solution as
>Hubble later proved by observation.
>
>It is ironic that with improved observational data the same constant now
>seems to be making the universe fly apart at beyond exponential rate.
>I'm no great fan of "dark energy" but I am told by my friends still in
>the field that it is the least worst option now.
>
>It means matter and radiation in the universe will eventually become
>very very thin indeed as spacetime rips apart ever more rapidly with time.
>
>TBH I'd prefer there to be something wrong with the Type Ia supernovae
>standard candles in the early universe (making them overly bright).
>
>https://en.wikipedia.org/wiki/Type_Ia_supernova
>
>I understand that possibility has been ruled out but I don't know any
>more details. They are very handy since when they go off they can
>outshine an entire galaxy and are visible over huge distances.
>
>You can measure the light curve and determine absolute brightness from
>it provided that you catch it early. Amateur astronomers help the
>professionals by monitoring galaxies and reporting events in realtime.
>
>Pro scopes only divert to look at them if there is something to see.
>(although there are some professional supernova systems as well)
>
>The idea that the fundamental constants of nature might not be quite
>constant dates back to Dirac who was the first to make that conjecture.

I have been re-reading the article just now and do find it unclear.
In my view, when 'universe' or rather what we see or think it is, is starting with a bang so to speak
a Le Sage model, where the Le Sage particles originate from for example processes in stars
or maybe black holes, IMPLIES the universe flying apart ever faster,
no mysterious 'dark energy', just simple physics.
It explains many other things too, like clocks slowing down in a gravity well (near some object), etc
And of course there must? have been multiple big bangs / universes and some of what we see may be from expansion of those?
Keep it simple.
Le Sage particles - or a state of those - could be EM radiation, that would then explain why gravity moves at the speed of light.
And of course, as things slow down over time, light speed and gravity may vary too over time.

On Fri, 5 Apr 2024 09:17:23 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:

>On 05/04/2024 06:17, Jan Panteltje wrote:
>> Dark energy might not be constant after all
>> First results from the Dark Energy Spectroscopic Instrument offer hints of new physics.
>> https://arstechnica.com/science/2024/04/dark-energy-might-not-be-constant-after-all/
>
>"Dark energy" is the constant that Einstein had to introduce into his
>equations for the Universe to make a "Steady State Universe" model work.
>
>The default solution to Einstein-Lemaitre was an exponentially expanding
>one which he didn't much like. He described it as his greatest mistake
>since reality was much more like his original equation solution as
>Hubble later proved by observation.
>
>It is ironic that with improved observational data the same constant now
>seems to be making the universe fly apart at beyond exponential rate.
>I'm no great fan of "dark energy" but I am told by my friends still in
>the field that it is the least worst option now.
>
>It means matter and radiation in the universe will eventually become
>very very thin indeed as spacetime rips apart ever more rapidly with time.
>
>TBH I'd prefer there to be something wrong with the Type Ia supernovae
>standard candles in the early universe (making them overly bright).
>
>https://en.wikipedia.org/wiki/Type_Ia_supernova
>
>I understand that possibility has been ruled out but I don't know any
>more details. They are very handy since when they go off they can
>outshine an entire galaxy and are visible over huge distances.

10^44 joules could fry a thousand civilizations. We're lucky to live
in a boring suburb of the universe.

Are those things the sources of our heavy elements?

On 6/04/2024 1:28 am, John Larkin wrote:
> On Fri, 5 Apr 2024 09:17:23 +0100, Martin Brown <'''newspam'''@nonad.co.uk> wrote:
>> On 05/04/2024 06:17, Jan Panteltje wrote:

> 10^44 joules could fry a thousand civilizations. We're lucky to live
> in a boring suburb of the universe.

Supernova pop up all over - just not all that often. There's nothing
unique about our suburb of the universe - corner of the galaxy might be
a better way of referring to our immediate vicinity

> Are those things the sources of our heavy elements?

That seems to be the current working hypothesis. Anything up to iron -
26 protons and 30 neutrons in the most common isotope Fe-56 (91.754%)

<https://en.wikipedia.org/wiki/Isotopes_of_iron>

can be synthesised in mainstream star, but it has the largest mass
defect of any element. Fe-54, Fe-57 and Fe-58 are the other stable isotopes.

Getting anything heavier takes a supernova - gravitational pressure
exceeds nuclear repulsion and all the matter at the core of the star
collapses into neutron soup, but if the star isn't heavy enough to
become a black hole the collapsing soup that was moving inward very fast
until it hit it's density limit mostly bounced back out again and
reverted from neutron soup to regular matter that included a lot of
elements heavier than iron. The heaviest ones fissioned rapidly, but
rest provide all the elements from iron upwards to uranium and the like.

They weren't there in the very early universe, and the second generation
stars don't have all that much of them.

--
Bill Sloman, Sydney

On 05/04/2024 15:28, John Larkin wrote:
> On Fri, 5 Apr 2024 09:17:23 +0100, Martin Brown
> <'''newspam'''@nonad.co.uk> wrote:
>
>>
>> TBH I'd prefer there to be something wrong with the Type Ia supernovae
>> standard candles in the early universe (making them overly bright).
>>
>> https://en.wikipedia.org/wiki/Type_Ia_supernova
>>
>> I understand that possibility has been ruled out but I don't know any
>> more details. They are very handy since when they go off they can
>> outshine an entire galaxy and are visible over huge distances.
>
> 10^44 joules could fry a thousand civilizations. We're lucky to live
> in a boring suburb of the universe.

The safe distance for a supernova explosion is estimated to be around 25
ly by the optimists and 250 ly by the pessimists. The true value is
probably somewhere in between those two and not all supernovae are type
I other sorts can be even more potent.

https://www.skyatnightmagazine.com/space-science/how-close-supernova-affect-life-earth

I recall a famous researcher in this field who gave a somewhat whimsical
popular science talk on type Ia supernovae entitled "Can a young blue
giant find lasting happiness in the arms of a degenerate white dwarf?"
(spoiler alert - no they can't the liasson won't last!)

Betelgeuse and eta Carina are both candidates for going pop in the not
too distant future and are already bright stars in our night sky. They
will be daylight objects when they go bang possibly even as bright as
the moon but point sources.

> Are those things the sources of our heavy elements?

Supernovae and ultra massive stars are. Very massive stars can
endothermically make heavier elements than iron by slow neutron capture
but they are doomed to implode as supernovae when they finally run out
of fuel. They collapse on the free fall timescale due to gravity and the
core collapse can go to either a neutron star or black hole depending on
the total mass. The rebound shockwave distributes the remains of the
star into a shell supernova remnant of which the brightest in the night
sky is Cassiopiea A. It looks for all the world like a hand grenade went
off with an expanding shell of material around it.

https://public.nrao.edu/gallery/cassiopeia-a/

It would be about 1/5 the size of the moon if we could see in 6cm waveband!

Ultra massive stars become red giants in their final stages and aren't
too good at holding onto their atmospheres so there is a lot of material
that doesn't end up in the implosion but gets spread out into space.
Only the mostly iron core undergoes collapse and implosion and a
proportion of that material rebounds due to shockwave reflections.

--
Martin Brown