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n2doc

(47,953 posts)
Thu Oct 31, 2013, 10:12 AM Oct 2013

Physics: What We Do and Don’t Know

Steven Weinberg


In the past fifty years two large branches of physical science have each made a historic transition. I recall both cosmology and elementary particle physics in the early 1960s as cacophonies of competing conjectures. By now in each case we have a widely accepted theory, known as a “standard model.”

Cosmology and elementary particle physics span a range from the largest to the smallest distances about which we have any reliable knowledge. The cosmologist looks out to a cosmic horizon, the farthest distance light could have traveled since the universe became transparent to light over ten billion years ago, while the elementary particle physicist explores distances much smaller than an atomic nucleus. Yet our standard models really work—they allow us to make numerical predictions of high precision, which turn out to agree with observation.

Up to a point the stories of cosmology and particle physics can be told separately. In the end, though, they will come together.


much much more

http://www.nybooks.com/articles/archives/2013/nov/07/physics-what-we-do-and-dont-know/

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Physics: What We Do and Don’t Know (Original Post) n2doc Oct 2013 OP
Love Weinberg. A good read. R&K nt longship Oct 2013 #1
That is fascinating Blue Owl Oct 2013 #2
Very good drawing together of Cosmology and Particle physics mindwalker_i Oct 2013 #3

mindwalker_i

(4,407 posts)
3. Very good drawing together of Cosmology and Particle physics
Thu Oct 31, 2013, 01:59 PM
Oct 2013

To date, I have yet to see any theory that attempts to deal with entanglement. For example, string theory postulates these little loops of something that vibrate to become each of the different types of particles, but it doesn't, as far as I have seen, deal with the fundamental aspect of the universe being non-local, a.k.a. entanglement. The many worlds interpretation of quantum mechanics doesn't seem to deal well with entanglement either. Even quantum superposition seems to pose big problems for these: if a photon is in a superposition state for its position/momentum and is aimed such that it might hit a mirror, at least initially it goes both ways and is both reflected and not reflected. At some time, it will interact with something, the wave function will collapse, and it will decide what it's position/momentum was and whether it reflected off the mirror or not. The many worlds interpretation was invented to handle this situation, but I can't see how string theory would deal with it. If there's an entangled photon, their momentums have to both collapse, and many worlds doesn't addess that.

My own hairbrained theory, if it can be called that as opposed to just a feeling, is that, before the big bang, there was no space, no time. So when the big bang happened, stuff didn't expand into already existing space, it created space as it expanded, as well as time. So "before" the big bang, there was something with physics that didn't say anything about space or time, then the big bang happened, creating both as well as physics that included space and time. If so, then quantum mechanics seems to be, at least to some extent, the non-space-time physics. It's the physics of the underlying "substrate" upon which spacetime exists on top of, or possibly spacetime is an emergent property of the underlying physics, which may be QM. There are definitely a lot of unsubstantiated ideas here, but if this line of reasoning is correct, then it makes sense that QM would show physical properties that a different and in disagreement with relativity, which deals with spacetime in a classical way.

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