Occam's Machete: Cosmology

Since Einstein we have known that gravity was somehow special. Physicists have a unified standard model of forces and elementary particles but everyone knows that the big problem is gravity. String theory contains gravitons and explains gravity like any of the other forces. But String theory has a lot of things, in fact it is more a tool set or framework than a single theory.

But what if gravity is just a shadow on the cave wall? Or, to put it in terms a physicist would use, what if gravity is emergent—the holographic affect of entanglement entropy? I have written about it before because the idea seems to be gaining steam, at least among wannabe crackpots (like me perhaps).

Ted Jacobson (no crackpot) wrote the seminal paper in 1995 describing how to derive Eistein’s General Relativity equations from, “the form of black hole entropy together with the fundamental relation Q = TdS.” It is a short elegant paper that has been sited often of late. Back in 1995 it was pretty hard for an amateur to follow controversy in the physics world so I didn’t notice a big reaction to Jacobson.

Then came Verlinde who shook things up in January of this year. I’ve already written about the reaction.

Verlinde seems to have started a lot of people thinking because there have been several new papers jumping on the bandwagon (1,2). In a recent FQXi post Vlatko Vedral shills his own coverage of the territory in his book, Decoding Reality.

I adopted his (Jacobson’s) logic in my book to suggest, with a tongue in cheek, that gravity can in fact be derived from information theory (albeit with a little bit of help from quantum entanglement). Vlatko Vedral.

For whatever intuition is worth, the ideas of entropy (which is tied to the arrow of time) and entanglement (spooky action at a distance) do seem to be special too.  And wasn’t it that honored cosmologist David Brin who said our universe is just a gigantic simulation?

Update: FQXi covers several of the papers and posts you’ve seen here but you might like the writing better. Check it out.

One foundational element of modern cosmology is inflation theory. It states that shortly after the big bang the entire universe started expanding faster than the speed of light. It eventually slowed down and recently we have discovered that it is speeding up again. The original form of inflation was proposed by Alan Guth and explains many things we observe about the universe including why it seem to be so uniform.

An interesting side effect of this expansion is that the further an object is away from the observer the faster the two are moving apart.  That means for very distant object they seem to be receding at faster than the speed of light, which in turn makes them invisible to us.  If you look out into the universe far enough you will reach the limit of what we can see. There is only so far that light can have traveled in the 13.7 billion years since the big bang.  But it is very likely there is stuff out there past the observable edge of what we can see.

This became more than speculation when it was recently noted that many galaxy clusters at the observable limit are rushing toward a point that appears to be beyond what we can see. Something big is out there sucking things towards it. Spooky! And here is a picture showing the action.

Nearby galaxy clusters are moving towards the purple dot.

An article in SPACE.com quoted Kashlinsky, the discoverer of the dark flow effect, as saying:

The structures responsible for this motion have been pushed so far away by inflation, I would guesstimate they may be hundreds of billions of light years away, that we cannot see even with the deepest telescopes because the light emitted there could not have reached us in the age of the universe.

Depending on your favorite flavor of Inflation Theory these structures may be very strange indeed.  if they can have an influence over billions of light year on more than 700 of galaxy clusters then they must be pretty big.