Holometer rules out first theory of space-time correlations

[danbruc]

Probably biased by the physicist I mostly listen to because they have a lot of lectures and talks online, Leonard Susskind and Nima Arkani-Hamed.

The idea that space is quantized is pretty unlikely to be true because of relativity, i.e. because of length contraction the size of those space quanta depends on the motion of the observer. So if you find those space quanta have a specific size in your reference frame I can just go to a reference frame moving relative to yours and I will see length contracted space quanta and we will therefore disagree on their size.

It is actually believed that neither space nor time are fundamental but that they emerge from something more fundamental because spacetime, relativity and quantum physics taken together are not really compatible, see for example "Space-time is doomed. What replaces it?" [1]. Susskind explores the idea that entanglement is what holds space together under the name "ER = EPR" [2].

[1] http://www.cornell.edu/video/nima-arkani-hamed-spacetime-is-...

[2] https://youtube.com/watch?v=OBPpRqxY8Uw

[vanderZwan]

I always wondered if Boulet's pixel-dream is an accurate depiction of the issues you run into if space is quantized:

http://www.bouletcorp.com/hidden/quantum-pixel/

[qrendel]

I'd be curious to know why the Planck length wouldn't be reference frame independent, though... (which may be explained in your links, but it will take some time to go through them).

[contravariant]

That just means it can't be quantized in a lattice-like structure, it can still be 'foam'-like with some characteristic length.

Also I'm not entirely convinced that space-time and quantum field theory are completely incompatible. General relativity and Yang-Mills (in the classical limit) fit beautifully together, it would be extremely odd if this becomes impossible when you add quantum physics.

[mstade]

Great links, thank you very much!

[qrendel]

> If the universe were similarly segmented, then there would be a limit to the amount of information space-time could contain.

I thought there is a limit to the amount of information spacetime can contain: the Bekenstein bound[1], and its variations[2]. Though it's related to the surface area bounding the region, and not the volume enclosed itself. For a spherical cubic cm, about 10^66 bits, iirc.

[1] https://en.wikipedia.org/wiki/Bekenstein_bound

[2] http://www.scholarpedia.org/article/Bekenstein_bound

[lpage]

I'm wondering about that as well. The closely related covariant entropy bound is predicated on both the holographic principle and our current understanding of quantum gravity, so I'm not sure if this finding calls that into question or not.

There was a good HN discussion on the theoretical limits of information density a few years ago: https://news.ycombinator.com/item?id=6466430

[powertower]

The results seem to disproves both:

1. A quantum foam space-time.

2. A networked/graphed space-time in which the nodes can have plank-scale (or larger) movements and re-arrangements.

But I'm not sure if this experiment disproves a space-time of fixed-position nodes which have additional properties (such as a field of scalars / vectors / spinors / etc).

To test the above I think measuring the smallest possible change-of-angle that a laser can make off a reflective surface (compounded X times) would do well. If the arrangement is as above, rotating the reflective surface by the smallest amount will affect the produced angle in a non-linear way (compared to larger amounts).

[c-slice]

Also seems to provide evidence against simulated reality.

[Estragon]

Good to see someone getting some press for a negative result.

[jonbaer]

What I am wondering about is what the implications (and reactions) would have been if it were a positive result ...

[shmerl]

> If the universe were similarly segmented, then there would be a limit to the amount of information space-time could contain.

Not really, if those "pixels" are a countable set. Is still wouldn't be continuous, but it could hold any information. Symbolic elements ("pixels", letters etc.) actually are basis of information, so it kind of implies a discrete space when information is involved.

[graycat]

> countable

Maybe you have in mind countable dense?

[jonbaer]

The first time I learned about this project was from the BBC Documentary on Reality (excellent BTW) ... here is the holometer segment ... https://youtu.be/DbqB0--Td28?t=2346

[Kinnard]

This pairs very well with Stephen Wolfram's recent piece on the true nature of space-time: a network

https://news.ycombinator.com/item?id=10664272

Published acoincidentally on the 100th anniversary of Einstein's original General Relativity Paper.

[yCloser]

TL;DR: background-color: #e45950

[TranquilMarmot]

My eyes!

[barrystaes]

Reading how sensitive this equipment can measure short duration displacements, and the distance the laser beams travel.. I wonder if - and how - they would adjust this for the drift due to the earth rotating. (and its speed is not even constant)

[danbruc]

It's probably even way worse. I think it was one of the gravity wave experiments and they talked about how they picked up signals from people walking in neighboring building, cars driving on the highway and even the ocean waves hitting the beach while the beach was fifty or a hundred or so kilometers away. Maybe it's as simple as a high pass filter but I'd also like to know more about the details.

EDIT: It was probably not this exact article [1] but it matches my memories pretty well. They also mention some of the countermeasures.

[1] http://www.nature.com/news/physics-wave-of-the-future-1.1556...

[iopq]

I have not reached for the Inspect Element faster than seeing this abomination. Who thought that an all red webpage might be difficult on the eyes?

[ansgri]

This is more like 'salmon' than 'red'. Seems rather readable on a good display with low brightness. Unsafe choice for not art-specific website though.