
Is There Anything Beyond Quantum Computing? - ca98am79
http://www.pbs.org/wgbh/nova/blogs/physics/2014/04/is-there-anything-beyond-quantum-computing/
======
saalweachter
Hah.

So Roger Penrose, not content with the now-seemingly-attainable quantum
computing, speculates there is an even _more_ magical quantum gravity
computing, which brains just happen to use, that makes them special, that
Turing machines can't compute?

The man just really hates the idea of AI, doesn't he?

~~~
DennisP
That's nothing new for Penrose, he wrote about it in _Emperor 's New Mind_.
His whole argument is based on noncomputability, and he points out in the book
that ordinary quantum computers can't do the noncomputable.

And of course if he were right and we did figure out the physics of it,
there'd be nothing to prevent us from building hardware that uses the same
physics.

------
rhth54656
_But the more you accelerate the spaceship, the more energy you need, with the
energy diverging to infinity as your speed approaches that of light. At some
point, your spaceship will become so energetic that it, too, will collapse
into to a black hole._

That is simply wrong. It is called relativity for a reason. An object might be
traveling arbitrarily fast, but in its reference frame it is not moving.

That pretty much invalidates that part of the article.

For curious readers:
[http://physics.stackexchange.com/questions/3436/if-a-1kg-
mas...](http://physics.stackexchange.com/questions/3436/if-a-1kg-mass-was-
accelerated-close-to-the-speed-of-light-would-it-turn-into-a-b)

~~~
rohansingh
An object can accelerate arbitrarily, but in any reference frame it will never
be traveling faster than _c_.

Of course, it won't collapse into a black hole, but the amount of energy
needed to accelerate further will increase asymptotically.

~~~
rhth54656
That is actually false from the frame of the traveler. Using constant
acceleration, the traveler will observe constant energy usage. Then length
contraction will guarantee that you can reach speeds arbitrarily close to
speed of light( and also any location in the universe ) in about ~50 years
with 1G acceleration.

[http://en.wikipedia.org/wiki/Space_travel_using_constant_acc...](http://en.wikipedia.org/wiki/Space_travel_using_constant_acceleration#A_Half_Myth:_It_gets_harder_to_push_a_ship_faster_as_it_gets_closer_to_the_speed_of_light)

~~~
AnimalMuppet
Yes, but _when_ do you get there? In 50 years in your time, but it may be a
few billion years later in their time...

~~~
rhth54656
I believe that is the point. Even more time for the stationary computer to
finish the calculation.

------
calhoun137
The most important application of quantum computers seems to actually be to
enable scientists who do fundamental research to answer questions from
reporters such as "What practical purpose does your research serve?" with a
single catch all buzz word. So the answer to the title of this article is
clearly: Yes.

------
dmunoz
> What’s more, there are recent developments in quantum gravity that seem to
> support the opposite conclusion: that is, they hint that a standard quantum
> computer could efficiently simulate even quantum-gravitational processes,
> like the formation and evaporation of black holes. Most notably, the AdS/CFT
> correspondence, which emerged from string theory, posits a “duality” between
> two extremely different-looking kinds of theories. On one side of the
> duality is AdS (Anti de Sitter): a theory of quantum gravity for a
> hypothetical universe that has a negative cosmological constant, effectively
> causing the whole universe to be surrounded by a reflecting boundary. On the
> other side is a CFT (Conformal Field Theory): an “ordinary” quantum field
> theory, without gravity, that lives only on the boundary of the AdS space.
> The AdS/CFT correspondence, for which there’s now overwhelming evidence
> (though not yet a proof), says that any question about what happens in the
> AdS space can be translated into an “equivalent” question about the CFT, and
> vice versa.

If you would like to read more about this, the author of this article has
another blog post [0] that discusses the Susskind paper "Computational
Complexity and Black Hole Horizons" [1] in its first half.

They key point, for those who don't have time to read the post:

> On one side of the ring is AdS (Anti de Sitter), a quantum-gravitational
> theory in D spacetime dimensions—one where black holes can form and
> evaporate, etc., but on the other hand, the entire universe is surrounded by
> a reflecting boundary a finite distance away, to help keep everything nice
> and unitary. On the other side is CFT (Conformal Field Theory): an
> “ordinary” quantum field theory, with no gravity, that lives only on the
> (D-1)-dimensional “boundary” of the AdS space, and not in its interior
> “bulk.” The claim of AdS/CFT is that despite how different they look, these
> two theories are “equivalent,” in the sense that any calculation in one
> theory can be transformed to a calculation in the other theory that yields
> the same answer. Moreover, we get mileage this way, since a calculation
> that’s hard on the AdS side is often easy on the CFT side and vice versa.

[0]
[http://www.scottaaronson.com/blog/?p=1697](http://www.scottaaronson.com/blog/?p=1697)

[1] [http://arxiv.org/abs/1402.5674](http://arxiv.org/abs/1402.5674)

------
jamiis
If you liked this, checkout the interview "Scott Aaronson on Philosophical
Progress" [0]. Possibly my favorite read of last year.

[0]
[http://intelligence.org/2013/12/13/aaronson/](http://intelligence.org/2013/12/13/aaronson/)

------
diziet
Actual article is here:
[http://www.pbs.org/wgbh/nova/blogs/physics/2014/04/is-
there-...](http://www.pbs.org/wgbh/nova/blogs/physics/2014/04/is-there-
anything-beyond-quantum-computing/) but Scott's blog has the comment section

~~~
dang
I changed the article url. For those who want the comments, the original was
[http://www.scottaaronson.com/blog/?p=1781](http://www.scottaaronson.com/blog/?p=1781).

------
z3phyr
Neuromorphic Computing?
[http://en.wikipedia.org/wiki/Neuromorphic_engineering](http://en.wikipedia.org/wiki/Neuromorphic_engineering)

~~~
klodolph
That's just a different architecture for a classical, non-quantum computer.
(Keep in mind that analog computers came first, so this is a call back to the
first half of the 20th century, albeit on a much larger scale.)

~~~
3rd3
One thing we don't know is whether the brain is maybe able to perform
calculations on real numbers which could allow for different or even more
powerful calculations compared to the Turing machine.

~~~
klodolph
No.

The line of thinking is, "Well, if we had real numbers, we could compute
uncomputable functions." No shit. Most real numbers are not computable. If you
start with something not computable, you end up with something not computable.

The big problem is that there is no way you will get more than several digits
of precision on anything. The next problem is that there's zero evidence that
anything in the universe is capable of encoding an arbitrary real number, even
within a given bound. The last problem is that making a "real-number" machine
capable of solving a problem that a Turing machine can't basically requires
knowing the answer ahead of time and encoding it into the real-number machine
as a constant. Unclear how you'd do that.

~~~
3rd3
How I understood it, and please correct me if i am wrong, is that a machine
than can caluclate numbers with infinite precision in constant time has
certainly a time benefit, but not necessarily a broader class of computable
functions compared to a Turing machine. I interpreted z3phyr’s reference to
Wikipedia as a hint to that idea. But I agree that the most convincing
arguments are against the existence of such a machine.

(By the way, writing "No.\n\n" can be received as a rude response. I felt a
little bit uncomfortable reading it.)

~~~
3rd3
Oops, sorry for this comment. ("don't drink and internet")

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trhway
> If so, then much like in Zeno’s paradox, your computer would have completed
> infinitely many steps in a mere two seconds!

The next target isn't infinitely many. The target is infinitely infinitely
many.

Like something along the lines of forking infinite number of parallel
Universes - that is pretty much "many-verse" interpretation of the quantum
superposition(and thus computing) - enhanced with forking of infinitely many
time dimensions inside each of the said Universes...

~~~
dkarapetyan
Infinitely infinitely many is still infinitely many. N x N has the same
cardinality as N. Now if you meant N ^ N then that's actually different. "x"
means set product and "^" means function space.

~~~
Sniffnoy
This isn't about cardinality, though, this is about number of steps, which is
more properly measured with ordinal numbers. I'm not familiar with the theory
of infinite-time Turing machines, but it's at least plausible that there are
things you can do with omega^2 steps (or larger countable ordinals) that you
couldn't do with only omega steps.

~~~
sp332
omega == omega^2. They are the same quantity. For every element of omega^2,
there is a corresponding unique element of omega.

~~~
adamtj
Actually, no. I just recently read about this.

1 + omega == omega < omega + 1 < omega^2

[http://en.wikipedia.org/wiki/Ordinal_number](http://en.wikipedia.org/wiki/Ordinal_number)

~~~
sp332
Weird! Thanks for the link!

~~~
wfo
Actually you are both right -- omega and omega + 1 (or omega^2) have the same
'number' of elements (there is a one to one correspondence) but the
correspondence will not be (can not be) order-preserving. Ordinals are a
natural extension of the natural numbers. If you take the natural numbers and
add a new element that's bigger than all of them then you get a new structure
(called omega + 1) which has the same size as the normal natural numbers, but
has one new element which is order-distinguishable from all our normal
numbers. Some ordinals, which correspond to a jump in 'size' (like 2^omega)
are special and called cardinal numbers.

------
mrtriangle
Yes. Super Duper Computing.

~~~
EC1
I laughed.

------
Havoc
Scott is making it really difficult for people to follow along. My initial
reaction was "wtf am I looking at" followed shortly by "why wasn't the HN link
pointed straight to the PBS article?". And clearly others agree given that the
top comment at the moment is a PBS link.

No doubt the guy is competent but this just smells like a poorly executed
attempt to move traffic to the blog. I fully expect it to get ignored as such
despite the PBS article being good.

~~~
forgotprevpass
If you're not familiar, Scott is a professor of MIT, specializing in quantum
computing. Many readers of his blog are also well known in this sphere, so
they would have more technical insight, more in depth than the pbs layman's
version.

~~~
Havoc
>>If you're not familiar, Scott is a professor of MIT

As I said, I don't doubt his ability. Its the presentation I object to. The HN
blog leads to some random blog that barely touches on the topic that the
headline promises and the core of the story is in a link contained in the
blog. By any sane definition that is blog spam, MIT professor or not.

>>Many readers of his blog are also well known

So? Its linked to his blog, not to his readers. I don't care if his readers
include Albert Einstein himself. The link did not deliver despite the authors
(proven) ability to deliver on the content.

