

Researchers propose a way to build the first space-time crystal - Zenst
http://phys.org/news/2012-09-clock-space-time-crystal.html

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kibwen
Very interesting, I didn't realize if was possible for _anything_ to survive
the heat death of the universe. The answer to my immediate question:

 _"'While a space-time crystal looks like a perpetual motion machine and may
seem implausible at first glance,' Li says, 'keep in mind that a
superconductor or even a normal metal ring can support persistent electron
currents in its quantum ground state under the right conditions.' [ ... ] Li
is quick to point out that their proposed space-time crystal is not a
perpetual motion machine because being at the lowest quantum energy state,
there is no energy output."_

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smoyer
I was also thinking of this as a perpetual motion machine but perhaps the
slightest attempt to use force of the moving ions would cause the rotation to
stop. My non-physicist brain says if you have something that will move
forever, it sounds like free energy!

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Zenst
I believe that because we are talking about quantum effect energy, then it is
a case of any form of measuring would effect it. That is to say any attempt to
extract (which could be deemed a form of measuring/observing) any energy from
it would be at the expense of the source. Can think of it as quantum friction
if that helps. Perhaps a betetr way to explain it would be a atom, which has
the classic solarsystem effect with orbiting electrons. Now we have managed to
tap into that energy and that is the atomic bomb and later nucleur power
stations. Now you know in those cases the original source of material/energy
is changed and that is it in a nutshell, by measuring/observing/tapping into
that level of energy will effect it and in a way introduces friction into a
frictionless state of energy.

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alainbryden
So while it might survive the heat death of the universe, there could be no
way to measure it.

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ars
You would measure it by giving it energy, but not enough to perturb it. You
give it exactly as much as it gives back, so you don't cause any changes.

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beernutz
How would you read the state? If, at the lowest energy state, there is no
energy output, would even photons change the state? If so how would you read
the "time" from it?

Does that make any sense?

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jrajav
Via quantum entanglement, possibly? I honestly have no clue either, but they
hint at entanglement, and they don't seem to be worried about observation:

"Peng Zhang, another co-author and member of Zhang's research group, notes
that a space-time crystal might also be used to store and transfer quantum
information across different rotational states in both space and time."

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marshray
Can someone explain how this thing is different than an ordinary ring of like
atoms (e.g., benzene) rotating in a magnetic field?

What experiment can I perform to distinguish a "space-time crystal" from a
non-STC in ordinary peroidic motion?

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zan2434
Can you manipulate future and past states by manipulating the current state?
I'm not too knowledgeable about the matter but it seems like if the crystal's
states at certain points in time are fixed from its inception then it can be
manipulated to transfer information to future and past states of the crystal.

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VLM
Its only state is its very exotic looking ground state, at least compared to
all the other ground states I can think of at this moment. So no manipulating
the state because the definition of the thing is its a constant ground state.

There's a fun thermodynamic argument that does not fit in the margins of this
hacker news explaining why you can not transmit information by lowering
entropy on something already in its ground state.

As for transferring information in general, see "light cones". Going forwards
you can't send info further away than the speed of light would reach, and
going backwards there isn't much of a light cone...

This prevents information from being stored inside the system, but does not
prevent the system from being used "in bulk" as information storage. Crude
analogy is you could make a Turing machine where "mark" equals drop one of
these crystals on the tape "space" equals wipe it off or flip it upside down
or whatever. Or you could make essentially a punchcard by building a 10x10
array of them and smashing some of them in a pattern... theoretically the
unsmashed ones would never ever decay, and the smashed ones are too
complicated to spontaneously reform, so a large collection of them aligned in
certain patterns would actually make a pretty decent ultra long term storage
media.

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stcredzero
I can imagine some future analogue of Danny Hillis constructing one of these
things, entombed inside the a planet sized crystal extracted from the heart of
a gas giant, parked in intergalactic space. The purpose would be to save the
universe from heat death by ensuring that time will always have meaning.

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powertower
Is that entire article just trying to say that the ion-ring, which is in it's
lowest energy state, rotates at a perfect rate (will never speed up or slow
down) and hence you have the central peace of a very accurate time keeper?...

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sp332
Is the speed of the electrons quantized, or can you "tune" the period
continuously? Either would be useful.

