Expanding Universe Question

[Anonymous No.15165901]

Using Supernovas in 1998 they found out galaxies are farther from us than we thought. This didn't correspond well to closed universe or open universe but to an accelerated expansion.

My question is, we know how fast we are drifting apart, but why would a farther distance mean we are expansion is accelerating? It seems contradictory to me.
For example we know someone is traveling 100 mph we would assume he traveled 100 miles since the last hour, but if he traveled 110 miles we would assume he decelerated to 100 mph.
Can someone explain why I'm retarded?

[Anonymous No.15166300]

>>15165901
> If you are ever in a room full of physicists and astronomers and want to figure out which is which, ask each if they know how to calculate a “K-correction”. Both will know how to do it, but only the astronomers will know it by its name. The need for this correction arises when we measure the distance to a supernova from its brightness because the way we see a supernova is also affected by the universe’s expansion. Besides causing the redshift, cosmic expansion also dilates (expands) time intervals over which supernova light is collected, changes the size of the increments in brightness, and shifts the portion of the spectrum we observe. (A physicist would mutter about need for “relativistic corrections”). Brian and I iterated back and forth a few times before we were both comfortable applying these corrections. I later heard from members of the Supernova Cosmology Project that despite their own extensive study of these corrections, errors in making the correc- tions likely limited the accuracy of the analysis of their first seven supernovae. K-corrections are a tricky step.


Adam Riess, Nobel Lecture

[Anonymous No.15166303]

The speed of acceleration is constant but as the universe grows bigger the constant speed also gets bigger because it's moving more space than before

[Anonymous No.15166304]

cosmology isn't science

[Anonymous No.15166309]

>>15166303
relative to who? let’s say aan observer on earth is looking at two objects at a distance 1M light years for object A and 2M light years for object B. if the observer measures speed of object A and object B in one sitting then the two measurements correspond to the objects’ speeds at 1 and 2 million years ago only when the universe is not expanding or contracting. if the universe is accelerating or decelerating, then inferring what “time” those things were traveling at the measured speeds is nontrivial and computing their present speeds and accelerations is also nontrivial. please post an equation to relate measured speeds (red shifts) to inferred accelerations

[Anonymous No.15166319]

>>15166309

[Anonymous No.15166338]

>>15166319
what would i get if i fixed my typos and put in proper capitalization? does that enter into the algorithm?

typically these things are stingy on “verbal IQ” bullshit which i actively ignore since capitalization is a pointless ritual for schoolteachers to use as a midwife filter

[Anonymous No.15166406]

>>15166303
>The speed of acceleration is constant
wew lad

[Anonymous No.15166676]

It's not a stupid question, it's a rather subtle point. The basic reason why there is a difference is in how astronomers measure distance, which is with redshift.

If we take a very simple model and assume there is no acceleration or deceleration and the Hubble constant is fixed. If we see a galaxy at a redshift of z = 0.233, which is a recession velocity of 70,000 km/s. This is the velocity that comes from measuring the shift in the galaxies light with the expansion of the universe. If we believe the Hubble constant (H_0) is 70 km/s/Mpc then we infer a distance to this galaxy of 70000/70 = 1000 Mpc (megaparsecs). But what if the universe were expanding faster? Well, we still measured a redshift of z=0.233. So say, H=700 km/s/Mpc then the distance we estimate is only 100 Mpc. 10 times less. So we see that if the universe is expanding faster a given redshift implies a lower distance.

This also applies when thinking about acceleration, in this case we say the Hubble constant today is the same regardless. If the universe is decelerating then the Hubble parameter would be higher in the past. This means that a given redshift corresponds to a smaller distance than an accelerating cosmology.

In my previous distance calculation I used a local approximation, more generally we have to integrate the distance in the case of a variable Hubble parameter (H(z)).

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

You can see if you look at the equations used to calculate distance vs redshift in different cosmologies. The integral of comoving distance is the most important, other distances are related to it (such as the luminosity distance relevant for e.g. supernovea). It is related to the integral of 1/E(z) or H0/H(z). So you see if H(z) is higher in the past then the comoving distance is less.

[Anonymous No.15166677]

>>15166676
>>15166309

One can get a bit mixed up if you try to think of following the same galaxy in these two different cosmologies. But if the universe was suddenly expanding faster the redshift of these galaxies would change. You need to think in terms of the observations, a supernova was found at redshift z=x what distance would that imply in different cosmologies?

[Jealous No.15166683]

>>15165901
>My question is, we know how fast we are drifting apart, but why would a farther distance mean we are expansion is accelerating?
The acceleration is inferred from the distribution of galaxies observed at different red shifts. In cosmology, red shift is a proxy measurement for distance due to Hubble expansion. However, the observed distribution is not consistent with Hubble expansion because the data shows too many galaxies at higher redshift. The first way that people imagined this distribution could occur was if the spatial part of the universe was expanding increasing quickly as time goes by. However, exciting new data from the JWST shows that the properties of high-Z objects (high redshift) are more consistent with expansion in the time sector of spacetime rather than the space sector. (This was the main idea proposed in the paper which is now called SCP-001, btw.) In fact, I think the secret they aren't telling yet is that accelerating spatial expansion has been ruled out by the new data.

(It is possible that I have slightly oversimplified redshift as a proxy for distance. I am not sure exactly that I remember what data are sampled in the dark energy surveys but I think it's like I said.)

[Anonymous No.15166697]

>>15166683
Are you saying new data from the JWST has disproven the idea that space is expanding? That would be huge.

[Anonymous No.15166716]

>>15166697
No, it's complete bullshit. The predictions for number of galaxies with redshift depends entirely on how you assume galaxy formation works. Different models make different predictions. It's retarded to try and take the number of galaxies as a cosmological result.

[Anonymous No.15167125]

>>15166683
It's interesting that nobody agrees

[Anonymous No.15167133]

>>15165901
There's no real evidence. For all we know the laws of physics might actually be different in different places. There's no need for it to be the same as kikestein's theory

[Anonymous No.15167148]

>>15165901
It's like mideval peoples arguing endlessly about epicycles whereas a simpler (MOND in this case) explains it all away with relative ease

[Anonymous No.15167225]

>>15167148
Lol no. MOND does not work on cosmological scales at all. Pic related is a resealed prediction of the power spectrum of the cosmic microwave background. The CMB is a pillar of cosmology. Standard cosmology matched predictions exquisitely, MOND-based predictions did not. 20 years after the data started to diverge from MOND and there are still no answers. The only response has been to fudge it and to add more arbitrary modifications, and introduce a matter-like field (dark matter) to match the data. MOND only works for galaxies, even when you go slightly bigger to the scale of galaxy clusters it fails.

[Anonymous No.15167490]

>>15166304
this

[Anonymous No.15167518]

>>15166676
Thank you so much. I was able to make this graph with your example which made everything a lot clearer. I was so hung up on the concept of z I should have studied that a bit more before going through all of this.
Noticing a changing km/s/Mpc from the graph seems enough for me to deduce what the hell is going on.
Unfortunately I'm a mathlet and I was just hoping to understand it without learning calculus. I think just a slower constant and a faster constant was enough to get a grasp on it.

[Anonymous No.15167521]

>>15167518
oh and thanks everyone else. I will try to follow some of these other rabbit holes

[Anonymous No.15169272]

>>15167518
>low iq comic book fan thinks cosmology isn't fake science
pottery, low iqs are fucking stupid lol