Salil – I was speaking in terms of a TOE. I mean the old story is that here was Einstein developing a radically new theory of gravity – which was then confirmed by observation. As it seems to me, the newer theories don’t appear to have that level of falsifiability (Popper) because they are malleable enough to account for a farily large array of observed and hypothetical phenomena. I mean although people are still working out what LQG and String theory are, it would be nice to know, in the same way Eddington confirmed some of GR’s more innovative claims, that they’re on the right track.

Btw I really enjoyed this series - have you seen it yet?

Desi angle – good to see people like Ashketar and Sen front and centre in these new developments!

Just thought I’d add my two cents and clarify something about dark matter. For non-dark matter and energy, gravity is an attractive force. For dark matter or energy, it’s repulsive.

The universe is constantly cooling, therefore atomic particle motion is constantly slowing down. Therefore the particles emit lesser energy in the form of radioactive waves (light, , microwaves, xrays, gamma rays, etc). Till the temperature drops to absolute zero. At this point, all particle motion has stopped. Therefore there is no energy being emitted. Therefore the universe has no more energy, and all matter has come to a standstill. At this point, when there is only matter but no energy left in the universe, does the spacetime fabric still keep expanding ?

therodynamics doesn’t apply to a vacuum, which has no temperature (and most of the universe is hard vacuum). The expansion of the universe isn’t a thermodynamic effect, it’s the actual physical expansion of space. It’s like blowing up a balloon and measuring the distance between points on the surface as you inflate it, rather than like the distance between the gas molecules in the balloon (assuming you were increasing the volume of the balloon and not adding gas, that is).

The latter would cool the balloon off, due to thermodynamics, which is a function of kinetic energy. The former is a relativistic effect of the literal expansion of what Star Trek calls “the fabric of space” (which I think is a polyester-rayon-cotton blend that resists wrinkles and almost never needs ironing). The nature or (to some degree) size of the objects themselves aren’t changing; the actual amount of space between them IS, which is very counterintuitive to us earthbound types who think a mile is a mile (or, maybe more accurately, a kilometer is a kilometer).

The “anti-gravity” force they refer to isn’t really any such thing. It’s a side effect of the fact that the universe is expanding.

And the dark matter doesn’t do anything to gravity as a force, theoretical or otherwise. Its effects are gravitational, after all.

Badmash:

I don’t know how well theories like loop quantum gravity or string theory are able to account for the implied presence of dark matter

I don’t think there are any obvious implications for sting or loop theory from all this. There are several categories of dark matter being postulated, both baryonic and non-baryonic. The non-baryonic can be lumped into (yes, this is for real) Hot, Warm, and Cold. If you want to dig deeper, I’m happy to talk geek with you…but the upshot is that dark matter has implications for material structure formation, not so much for string theory. String theory may help validate the absence or presence of dark matter because of the way it deal with gravity in the first place (it’s a good workaround for issues stemming from dealing with forces on / from point-like particles).

An interesting way to look at it Jai. I rememeber Hawking talked about the same thing in A Brief history of Time (“who breathes fire into the equations?”) and more recently, the philosopher Nancy Murphy has talked about this as a way of understanding the divine attribute of immanace.

Anyway from my (shallow) reading of popular science over the last few years, it doesn’t really look like things are coming together for physics as was expected as recently as ten years ago. I don’t know how well theories like loop quantum gravity or string theory are able to account for the implied presence of dark matter (Saheli – any ideas?). Plenty of opportunities for young desi scientists, like Ananinda Sinha, to make their mark!