# The Universe is a Hologram

First my background: no physics, but Ph.D. in math. I was reading this article on Slashdot. It links to this Wikipedia page. The content of the Slashdot article is that some physicists believe the universe is a hologram, describable by a two dimensional system and some researchers have proposed a method to test this. The Wikipedia page says this is an outcome of some string theories. Now, I've been told that what many view as a failing of string theories is that they are not testable within sane energy levels. My question is whether this proposed experiment would now make string theories testable within reason. Thanks.

I find it hard to take this paper overly seriously because of this closing line:

Nevertheless, assuming that the universe is finite and therefore the resources of potential simulators are finite, then a volume containing a simulation will be finite and a lattice spacing must be non-zero, and therefore in principle there always remains the possibility for the simulated to discover the simulators.

The universe is not a computer in the classical sense of a computer, nor is it a simulation in that regard. As I try to make sense of the statements, the only reasonable conclusion that I come across is that if we were to make the claim of simulation, then the simulators are the observers themselves. Certainly as observers there are limits in our internal ability to model the external world. As finite physical beings, we do live in a world of cutoffs and limits. We also certainly view things as a projection, so holography is a natural consequence of our own physical condition.

The replacement of the space-time continuum with a lattice, as discussed in the paper linked in your article, might be viable if they were actually taking discrete space-time elements, but in most cases they are taking discrete space elements and evolving them over discrete time increments, so they really are not talking about discrete space-time but are talking about something that can only be understood as a newtonian approximation. This can be observed in the paper by the explicit statement:

The grid breaks Lorentz symmetry (and hence rotational symmetry),

As far as making string theory testable, it is now true that Lorentz symmetry is not broken since it has been experimentally verified to sufficient precision below the plank length. So if they are saying that tests of Lorentz symmetry are evidence for string theory then there may be some truth to it, however, that connection would have to be very carefully defined, and would certainly be controversial within current popular communities.

Note: Just to clarify my position, if I were to take a closed universe solution to GR, such as closed universe FLRW model I would accept this as a true definition of discrete space-time, however in most cases, the authors of papers about discrete space-time are really talking about discrete space, which is a trivially false starting position in my opinion.