Atoms of Space and Time (loop quantum gravity = faster than light speed?)

[papau]

http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=00012BDE-E7EA-1FD3-A7EA83414B7F012C

PHYSICS Atoms of Space and Time

We perceive space and time to be continuous, but if the amazing theory of loop quantum gravity is correct, they actually come in discrete pieces

By Lee Smolin

Little more than 100 years ago most people--and most scientists--thought of matter as continuous. Although since ancient times some philosophers and scientists had speculated that if matter were broken up into small enough bits, it might turn out to be made up of very tiny atoms, few thought the existence of atoms could ever be proved. Today we have imaged individual atoms and have studied the particles that compose them. The granularity of matter is old news.
In recent decades, physicists and mathematicians have asked if space is also made of discrete pieces. Is it continuous, as we learn in school, or is it more like a piece of cloth, woven out of individual fibers? If we could probe to size scales that were small enough, would we see "atoms" of space, irreducible pieces of volume that cannot be broken into anything smaller? And what about time: Does nature change continuously, or does the world evolve in series of very tiny steps, acting more like a digital computer?...continued at Scientific American Digital



Great Read!

But "proof" and/or experimental varification of implications seem to be zero - the Hawkings ad hoc black hole radiation is said to be developed but it sounded like a circle in terms of reasoning.

[nadinbrzezinski]

1. Does the digital version match the paper version

I mean I would love to read this

[papau]

2. yes, digital is same as what was printed in Jan issue - but

the article is only a nice easy word explanation of what these folks have been playing with for the last 20 years, ever since the melding of General Relativity and QM at black holes was shown to give answers like "infinite", and Hawkings developed his radiation from black holes should exist and we found it did exist - but the measured level was ad hoc as to why it was that level (but then I've lived my whole life with QM eq getting constants defined as something devided by zero - in which we then subsitute the experimental values - thereby finally "finding out" what a division by zero produces !!!!! :-) )

:-)

[nadinbrzezinski]

3. good, thanks

I write Sci Fi so yuo will understand why this is MUST reading

Speaking off working on a Time Travel story and have done a novel, the universe I developed has time travel in a central way.

But it nice to see that the science is starting to come out, and
String Theory and Chaos theory may also have soething to do with this

[Alex88]

4. A Question

Does the universe have a perimeter?

[papau]

5. which of the infinite number of universes are we measuring in 11 dimension

what is a perimeter in 11 dimension world of string theory?

and while "infinite" number of universes is incorrect - the limit may the total number of combinations possible from all of the quantum states since the beginning of time to the end of time - it is still a big number.

And if string theory dimensions are about a point and have no "length" - just some other characteristic we call a dimension for this excercise - does this add to the perimeter?

Do all dimensions above 4 reduce to no length?

and if perimeter limit us to 2 dimensions - what is it when I can measure the length of the material I use for a Mobius strip, but I have only a one sided, one edge item - is there a perimeter?

And if x, y, and z are dimensions that have length, but the others are just at points - if I choose say x and one of those dimemsions that only exist at a point, can I get a perimeter? - what am I enclosing? - or do I just have a length?

:-)

[Alex88]

6. Interesting

Thanks.

[On the Road]

7. Here's an Encyclopedia Entry

on Loop Quantum Gravity:

http://en2.wikipedia.org/wiki/Quantum_loop_gravity

And amazingly enough, it seems to be testable:

"Unlike string theory and M-theory, LQG makes experimentally testable hypotheses.

The path taken by a photon through a discrete spacetime geometry would be different from the path taken by the same photon through continuous spacetime. Normally, such differences should be insignificant, but Giovanni Amelino-Camelia points out that photons which have travelled from distant galaxies may reveal the structure of spacetime. LQG predicts that more energetic photons should travel ever so slightly faster than less energetic photons. This effect would be too small to observe within our galaxy. However, light reaching us from gamma ray bursts in other galaxies should manifest a varying spectral shift over time. In other words, distant gamma ray bursts should appear to start off more bluish and end more reddish. LQG physcists anxiously await results from space-based gamma-ray spectrometry experiments -- a mission set to launch in September, 2006."

Too bad more of the SciAm article cannot be read on the web. I might actually have to break down and subscribe. I guess that's the idea.