Today is Ada Lovelace Day
In accordance with the Pledge, I would like to recognize the work of Margaret Geller . She and John Huchra discovered the Great Wall. This is one of the largest objects in the universe: Over 500 million light years long. That is 5,000 times the diameter of our entire galaxy.
My contribution last year is here.
Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.
Don’t look for a free lunch. There are still rules:
….energy and momentum evolve in a precisely specified way in response to the behavior of spacetime around them. If that spacetime is standing completely still, the total energy is constant; if it’s evolving, the energy changes in a completely unambiguous way.
This has been known since the 1920’s, and I learned about it when I first seriously studied GR at Stanford in 1973. However, scientists now need to pay more attention to it. In recent decades astronomical observations have have revealed many more situations where the effects of general relativity are significant.
Mathematical details at Is Energy Conserved in General Relativity?
From Cosmic Variance:
Geoffrey Burbidge passed away yesterday afternoon. He was a giant in the field of astronomy and cosmology, and (despite himself) was one of the main contributors to the establishment of the standard Big Bang model of cosmology. He was perhaps best known for his work in stellar nucleosynthesis (encapsulated in the B2FH paper: Burbidge, Burbidge, Fowler, and Hoyle 1957, Rev. Mod. Phys. 29, 547), which in some sense established that we are all made of “star stuff”. There are few research papers that are widely known simply by their author’s initials (especially over 50 years later); the paper even has its own wikipedia page. (Off hand, the only other one I can think of is EPR.)
Deep. As the author wrote: “immortality will lose a lot of its appeal.”
The science is accurate. For details see the End of the Universe.
At USA Today you can see the title: Mystery solved: Dark energy isn’t there.
But in the body of the article it says:
The only problem is that for the equations to work, we must be “literally at the center of the universe, which is, to say the least, unusual,” says physicist Lawrence Krauss of Arizona State University in Tempe. “I think this is plausible mathematics, but it doesn’t seem physically relevant.”
So in order to get “mystery solved” you have to assume something that science has been moving away from ever since Copernicus.
Much more at Dark Energy: Still a Puzzle.
In accordance with the Pledge, I would like to recognize the work of Vera Rubin. She discovered most of the matter in the universe, an accomplishment that really should be better known.
Via Make.
Cosmologists Predict A Static Universe In 3 Trillion Years
“When Dutch astronomer Willem de Sitter proposed a static model of the universe in the early 1900s, he was some 3 trillion years ahead of his time.”
Via Slashdot.
The de Sitter universe was one of the first cosmological models devised using General Relativity, and is widely discussed in Gen Rel textbooks–I have several in the basement. Nice to see the classics are still relevant :-)>
From Hilbert Space to Dilbert Space, and beyond 