Causality as a fundamental property of the universe

nigelTheBold
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Causality as a fundamental property of the universe

Browsing the July 2008 Scientific American, I read an article concerning causal dynamical triangulations. I'm ashamed to admit I had not heard of CDT before, as I haven't been following quantum theory much over the last several years.

There are several intriguing aspects to CDT. The first is, it assumes nothing exotic or strange. This sets it apart from string theory, for example. Its basic ingredients are essentially those of Euclidean quantum gravity, an earlier approach that failed to properly predict the basic structure of the universe. CDT adds the concept of causality to the earlier Euclidean quantum gravity approach, and the results are proving to be both robust and accurate.

For instance, it is the first hypothesis to predict the four dimensions of spacetime from first principles. It also conforms to Einstein's general relativity, which is pretty amazing.

The way causality is handled is simply to assume that each simplex has an arrow of time, and that the arrows of time in adjacent simplexes line up, or flow in the same "direction." This means that causality is a first principle, and is not an emergent property of quantum dynamics.

Some other cool features of this approach: if correct, that means that the substance of the universe is fractal below a certain scale, and so there is no lower "resolution" to the universe. Also, at the lowest scales, there are only 2 dimensions, not 4. The dimensionality of the universe increases non-linearly as a function of scale, converging to 4 dimensions at a certain scale. Also, modifying the value of the basic assumptions gives the same final results, making this approach very robust.

This is the only article I've read on the subject, so I have no real opinions, other than to admit a certain amount of excitement. I've thought for years that string theory is too complex, and doesn't seem to do an adequate job of explaining fundamental properties of the universe. I'm glad to see other hypotheses are making headway into the problem of quantum gravity.

Of course, the introduction of causality as a fundamental property of the universe would dig the hole in which we can dump the body of QM woo. But that's just an added bonus.

"Yes, I seriously believe that consciousness is a product of a natural process. I find that the neuroscientists, psychologists, and philosophers who proceed from that premise are the ones who are actually making useful contributions to our understanding of the mind." - PZ Myers


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 Article wrote:Imagine our

 

Article wrote:
Imagine our elation when the number of dimensions came out as four (more precisely, as 4.02 ± 0.1). It was the first time anyone had ever derived the observed number of dimensions from first principles. To this day, putting causality back into quantum-gravitational models is the only known cure for the instabilities of superposed spacetime geometries.

Ho-lee-shit. Yeah, I have to read more about this. If this research works out, I'm going to have to change my tune with Eloise and Paisley, and neither of us will ever have to defend quantum uncertainty in the same terms again.

 

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fabulae! nil satis firmi video quam ob rem accipere hunc mi expediat metum. - Terence


nigelTheBold
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HisWillness

HisWillness wrote:

Ho-lee-shit. Yeah, I have to read more about this. If this research works out, I'm going to have to change my tune with Eloise and Paisley, and neither of us will ever have to defend quantum uncertainty in the same terms again.

Yeah. My thoughts exactically.

Of course, until it makes testable predictions, it's just speculation. But it already has way better success than string theory, just in describing the observed spacetime.

"Yes, I seriously believe that consciousness is a product of a natural process. I find that the neuroscientists, psychologists, and philosophers who proceed from that premise are the ones who are actually making useful contributions to our understanding of the mind." - PZ Myers


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 The thing I love best

 The thing I love best about theoretical physics is that someone besides me is doing it.  This is really cool.

 

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nigelTheBold wrote:Of

nigelTheBold wrote:

Of course, until it makes testable predictions, it's just speculation. But it already has way better success than string theory, just in describing the observed spacetime.

That's why I got all excited. I think there's a fair amount of math that's similar, but nothing with this kind of dramatic simulation (although arriving at 4-dimensions sounds almost too good to be true).

Saint Will: no gyration without funkstification.
fabulae! nil satis firmi video quam ob rem accipere hunc mi expediat metum. - Terence


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Wow.

Wow.

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*Shakes fist*Damn you! DAMN

*Shakes fist*

Damn you! DAMN YoooooOOOOOU!

 

I was quite enjoying my Many Worlds Interpretation. I think, however, this may very well knock MWI right out of the ballpark (...and Coppenhagen along with it).

I wonder how we might test it, though?

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Kevin R Brown wrote:I wonder

Kevin R Brown wrote:

I wonder how we might test it, though?

So far, that's been the problem with every hypothesis surrounding quantum mechanics. How do you test it? At the moment, CDT hasn't predicted anything novel. BUT: it's predicted many things we take for granted, which is way better than string theory (the leading [in terms of research dollars] hypothesis).

We wait. It will eventually either predict something novel (which we can test) or not. Either way, it's far ahead of any other hypotheses, in that it matches observed reality with few suppositions.

But you are right. Until it predicts something new, something we do not know, it is untestable. Really, right now it has two strengths: that it predicted 4 demensions, and the cosmological constant. But honestly, that's 2 predictions more than string theory.

"Yes, I seriously believe that consciousness is a product of a natural process. I find that the neuroscientists, psychologists, and philosophers who proceed from that premise are the ones who are actually making useful contributions to our understanding of the mind." - PZ Myers


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nigelTheBold wrote:you are

nigelTheBold wrote:

you are right. Until it predicts something new, something we do not know, it is untestable. Really, right now it has two strengths: that it predicted 4 demensions, and the cosmological constant. But honestly, that's 2 predictions more than string theory.

 

Which is the number 2 problem I've had with string theory for a while (number 1 being I can't understand it).  I'm a big fan of anything that can make a prediction, even something known, from first principles.  It'll be interesting to see where this leads.

 

 

 

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HisWillness wrote: Article

HisWillness wrote:

 

Article wrote:
Imagine our elation when the number of dimensions came out as four (more precisely, as 4.02 ± 0.1). It was the first time anyone had ever derived the observed number of dimensions from first principles. To this day, putting causality back into quantum-gravitational models is the only known cure for the instabilities of superposed spacetime geometries.

Ho-lee-shit. Yeah, I have to read more about this. If this research works out, I'm going to have to change my tune with Eloise and Paisley, and neither of us will ever have to defend quantum uncertainty in the same terms again.

 

I can't speak for Paisley, but I'm not too perturbed by this at all. That you think I might be, Will, just demonstrates to me that I still have a lot of explaining to do in spite of our many long, and generally fruitful, discussions.


I read about CDT last year and I found the result, frankly, reassuring for my own part.  That Euclidean Quantum Gravity can work, with some prodding, is not the least of all the comforting aspects of this model.

More specifically however, that - a causal arrow, defined principally, generates something which matches our observations - I believe has a more profound explanation than, as suggested, that this one form of triangulation in shared time is something fundamental to existence itself. Fundamental to our observations, indeed I agree, but I have other ideas about anything deeper than that.

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Eloise: Demonstrating, once

Eloise: Demonstrating, once again, that no matter how explicitly science might detail our universe (or multiverse), people will still pretend God is somewhere in it. Sticking out tongue

 

(Just giving you a hard time. Eye-wink )

Quote:
"Natasha has just come up to the window from the courtyard and opened it wider so that the air may enter more freely into my room. I can see the bright green strip of grass beneath the wall, and the clear blue sky above the wall, and sunlight everywhere. Life is beautiful. Let the future generations cleanse it of all evil, oppression and violence, and enjoy it to the full."

- Leon Trotsky, Last Will & Testament
February 27, 1940