After reading a paper by Ashtekar on quantum gravity and thinking about it, I realized what my trouble with the Big Bang theory was. It is more on the fundamental assumptions than the details. I thought I would summarize my thoughts here, more for my own benefit than anybody else’s.
Classical theories (including SR and QM) treat space as continuous nothingness; hence the term space-time continuum. Theo quan điểm này, objects exist in continuous space and interact with each other in continuous time.
Although this notion of space time continuum is intuitively appealing, it is, at best, incomplete. Consider, ví dụ, a spinning body in empty space. It is expected to experience centrifugal force. Now imagine that the body is stationary and the whole space is rotating around it. Will it experience any centrifugal force?
It is hard to see why there would be any centrifugal force if space is empty nothingness.
GR introduced a paradigm shift by encoding gravity into space-time thereby making it dynamic in nature, rather than empty nothingness. Do đó, mass gets enmeshed in space (và thời gian), space becomes synonymous with the universe, and the spinning body question becomes easy to answer. Có, it will experience centrifugal force if it is the universe that is rotating around it because it is equivalent to the body spinning. Và, không, it won’t, if it is in just empty space. Nhưng “empty space” doesn’t exist. In the absence of mass, there is no space-time geometry.
Vì vậy,, tự nhiên, before the Big Bang (if there was one), there couldn’t be any space, nor indeed could there be any “before.” Note, Tuy nhiên, that the Ashtekar paper doesn’t clearly state why there had to be a big bang. The closest it gets is that the necessity of BB arises from the encoding of gravity in space-time in GR. Despite this encoding of gravity and thereby rendering space-time dynamic, GR still treats space-time as a smooth continuum — a flaw, according to Ashtekar, that QG will rectify.
Bây giờ, if we accept that the universe started out with a big bang (and from a small region), we have to account for quantum effects. Space-time has to be quantized and the only right way to do it would be through quantum gravity. Through QG, we expect to avoid the Big Bang singularity of GR, the same way QM solved the unbounded ground state energy problem in the hydrogen atom.
What I described above is what I understand to be the physical arguments behind modern cosmology. The rest is a mathematical edifice built on top of this physical (or indeed philosophical) nền tảng. If you have no strong views on the philosophical foundation (or if your views are consistent with it), you can accept BB with no difficulty. Không may, I do have differing views.
My views revolve around the following questions.
- Không gian là gì?
- Why is the speed of light important in it?
- Where does the Heisenberg Uncertainty Principle come from?
These posts may sound like useless philosophical musings, but I do have some concrete (and in my opinion, important) results, listed below.
- Are GRBs and Radio Sources Luminal Booms? (An article published in IJMP-D, which became one of the “Top Accessed Articles” of the journal. :-))
- Thời gian đi hiệu ứng ánh sáng và tính năng vũ trụ (Trying to get this one published.)
There is much more work to be done on this front. But for the next couple of years, with my new book contract and pressures from my quant career, I will not have enough time to study GR and cosmology with the seriousness they deserve. I hope to get back to them once the current phase of spreading myself too thin passes.