Looking for defunct papers/theories

  • Thread starter Thread starter Beer w/Straw
  • Start date Start date
AI Thread Summary
The discussion explores two defunct theories: one suggesting that time could run backward if the universe undergoes a big crunch, and the other focusing on Einstein's cosmological constant, which he abandoned after the discovery of an expanding universe. The backward time theory is linked to entropy reversing during a collapse, while the cosmological constant was initially used to create a static universe model. As the universe's expansion was confirmed, the need for the constant diminished, but later observations revealed the universe's acceleration, prompting a reevaluation of the constant's significance. Participants clarify that while Einstein's original idea was not revived, it has been reinterpreted in light of new evidence. The thread also touches on the accessibility of historical scientific papers online.
Beer w/Straw
Messages
49
Reaction score
0
Shot in the dark here, don't really know if these exist.

1. An idea that time would run backward if the universe would to undergoa big crunch. Think Stephen Hawking did this but abandoned the idea when the math was tested via computer.

2. Cosmological Constant by Einstien. Abandoned it long ago when Edwin Hubble documented the universe was expanding. This one intrigues me cause when HST documented the universe expansion to be accelerating (dark energy) and that Einstein's idea had been given a second to try and make sense of it.

Any help would be cool cause I'm curious :)
 
Last edited:
Space news on Phys.org
Beer w/Straw said:
Shot in the dark here, don't really know if these exist.

1. An idea that time would run backward if the universe would to undergoa big crunch. Think Stephen Hawking did this but abandoned the idea when the math was tested via computer.

This was certainly a legitimate idea. Not sure if it was proposed by Hawking, but I remember reading about it likely in the same place as you: A brief history of time. The idea (if I recall, it's been a few years) was that the entropy arrow of time should reverse as the universe begins to collapse.

2. Cosmological Constant by Einstien. Abandoned it long ago when Edwin Hubble documented the universe was expanding. This one intrigues me cause when HST documented the universe expansion to be accelerating (dark energy) and that Einstein's idea had been given a second to try and make sense of it.

Any help would be cool cause I'm curious :)

The cosmological constant as proposed by Einstein and that of the current accelerating universe really aren't that related, and it often bugs me when people say they are. Einstein noted that he could attempt to choose the cosmological constant (just an arbitrary term in his equations) so as to make the universe static -- what (then) current observational evidence pointed to. Once the universe was shown to be expanding, there was no need to hand-pick a specific value of the constant, and I think most people assumed it was zero for the simplicity of the theory and lack of observational evidence otherwise.

Then of course we found out the universe is accelerating which can be modeled by the same term in Einstein's equations, but the interpretation is somewhat different. For one, we can now attempt to make sense of this parameter in terms of known physics, i.e quantum field theory. Although quantum field theory gives an absurdly wrong result for the numerical value of the constant, it's at least a step towards understanding what the parameter might mean physically.

So it's not exactly like Einstein's idea was revived or anything, observational evidence simply clarified the value of a parameter in his equations.
 
Thanks for the reply. I'm going to look closely at some wiki articles.

Didn't think I'd get a reply actually.
 
I posted the above awhile ago in general science... Aside from cosmology I was also interested in finding historical papers ie Neils Bohr, Richard Feynman... Are such things accessible via internet?
 
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
The formal paper is here. The Rutgers University news has published a story about an image being closely examined at their New Brunswick campus. Here is an excerpt: Computer modeling of the gravitational lens by Keeton and Eid showed that the four visible foreground galaxies causing the gravitational bending couldn’t explain the details of the five-image pattern. Only with the addition of a large, invisible mass, in this case, a dark matter halo, could the model match the observations...
Hi, I’m pretty new to cosmology and I’m trying to get my head around the Big Bang and the potential infinite extent of the universe as a whole. There’s lots of misleading info out there but this forum and a few others have helped me and I just wanted to check I have the right idea. The Big Bang was the creation of space and time. At this instant t=0 space was infinite in size but the scale factor was zero. I’m picturing it (hopefully correctly) like an excel spreadsheet with infinite...
Back
Top