January 19, 2010

FROM THE ARCHIVES: OUGHTN'T WE DIG UP GALILEO AND BURN THE CORPSE? (via AOG)

Exploring Stephen Hawking's Flexiverse (Amanda Gefter, 20 April 2006, New Scientist)

Hawking and Hartle's original work on the quantum properties of the cosmos suggested that imaginary time, which seemed like a mathematical curiosity in the sum-over-histories approach, held the answer to understanding the origin of the universe.

Add up the histories of the universe in imaginary time, and time is transformed into space. The result is that, when the universe was small enough to be governed by quantum mechanics, it had four spatial dimensions and no dimension of time: where time would usually come to an end at a singularity, a new dimension of space appears, and, poof! The singularity vanishes.

In terms of the universe's history, that means there is no point A. Like the surface of a sphere, the universe is finite but has no definable starting point, or "boundary". Hence the idea's name: the no-boundary proposal.

This has led Hawking to define a new kind of cosmology. The traditional approach, which Hawking calls "bottom-up" cosmology, tries to specify the initial state of the universe and work from there. This is doomed to fail, Hawking says, because we know nothing about the starting conditions. Instead, he suggests, we should use the no-boundary proposal to do "top-down" cosmology, where the only input into our models of the universe comes from what we observe now - together with the idea that our universe has no boundary in the past.
Improbable tuning

The result of this process, he says, solves a long-standing problem of cosmology: fine-tuning. Most cosmologists think, for example, that the universe went through an early burst of rapid expansion, or "inflation". There is some evidence to support the claim, but there's also a problem. Standard inflationary models require a very improbable initial state, one that must have "finely tuned" values that cause inflation to start, then stop in a certain way after a certain time: a complicated prescription whose only justification is to produce a flat universe without any strange topology, and so on - a universe like ours.

Such a prescriptive method makes hard and unsatisfying work of producing the universe we see today. While a cosmologist can put these values into the equations "by hand", it is not exactly a satisfactory way to develop our model of how the universe works. In the no-boundary theory, however, there simply is no defined initial state. "In the usual approach it is difficult to explain how inflation began," says Hawking. "But it occurs naturally in top-down with the no-boundary condition. It doesn't need fine tuning."

To do top-down cosmology, Hawking and Hertog first take a whole raft of possible histories, all of which would result in a universe with features familiar to us. "We then calculate the probability for other features of the universe, given the constraints," Hertog says. Specify a universe that is three-dimensional and flat, for instance, and you can have histories that involve inflation and histories that don't. "Top-down cosmology does not predict that all possible universes have to begin with a period of inflation, but that inflation occurs naturally within a certain subclass of universes," Hertog says. The process creates a probability for each scenario, and so Hertog can see which kind of history is most likely. "What we find is that the inflating histories generally have the largest probability."

In many ways, top-down cosmology is an unsettling idea. Usually, science demands that our observations come out as output - we certainly don't expect them to be the input. That, after all, denies us the chance to see if the theory matches up with observations. What's more, the sum over histories is formed by calculating the various probabilities for a universe like ours to arise out of literally nothing: that means we can never know anything for certain about how our universe got to be as it is.

We shouldn't be surprised, Hertog says: quantum theory has long shown us that it is impossible for us to know everything about the world around us. In "classical" physics, we can predict both the exact momentum and position of a particle at any time, but quantum mechanics doesn't allow it. No one suggests that quantum mechanics is wrong because of this, Hertog points out - and experiments have shown that it is not. What quantum theory has given us now, Hertog says, is some indication about the nature of inflation, where before we had none. "Before, we had no prediction at all - and indeed no notion of likeliness - on this issue."

For many, it remains a difficult argument to swallow. Science since Copernicus has aimed to model a universe in which we are mere by-products, but top-down cosmology turns that on its head, rendering the history of the universe a by-product of our observations. All in all, it is very like the "anthropic landscape" argument that is causing controversy among string theorists (see "Putting the you into universe").

Princeton University physicist Paul Steinhardt is certainly unimpressed by Hawking and Hertog's scheme. "It's kind of giving up on the problem," he says. "We've all been hoping to calculate things from first principles. Stephen doesn't think that's possible, but I'm not convinced of that. They might be right, but it's much too early to take this approach; it looks to me like throwing in the towel."

Stanford University's Andrei Linde is similarly unconvinced. There are a number of technical assumptions that make him sceptical. "I don't buy it," he says.

The merits of Hawking and Hertog's new approach to cosmology might be decided by experiment. The theory predicts specific kinds of fluctuations in two cosmological phenomena: the cosmic microwave background radiation produced just after the big bang, and the spectrum of primordial gravitational waves. These fluctuations arise from applying the uncertainty principle of quantum mechanics to Hawking and Hertog's scheme: in this scenario, the universe's shape is never precisely determined, but is influenced by other histories with similar geometries.

If Hawking and Hertog are right, quantum uncertainty will manifest as slight differences from what standard inflationary theory predicts for the CMB. The top-down predictions only differ from the standard cosmological model at a level of precision that has not yet been reached in observations, however. The top-down signature in the gravitational wave spectrum should be easier to differentiate, but since we haven't yet detected any gravitational waves, we'll have to wait for that proof too.

For Hawking and Hertog, there's simply no doubt that top-down cosmology is the only answer. It's simple: if you can't know the initial state of the universe, you can't work forwards from the beginning: the top-down approach is the only one that works.

Hartle agrees. Hawking and Hertog's scheme may seem strange, but it is the only way forward because we are part of the experiment we are trying to observe. "It's a different viewpoint, but it's sort of inevitable," he says. "Colsmologists certainly should be paying attention to this work."

The trouble, of course, is that if they are right, we're involved in the making of that history. In that case, we have a new set of instructions for building a universe. Step one: look around you. Step two: find the set of all possible histories that end up as a universe like the one you see. Step three: add them together and create a history for yourself.


It's entirely predictable that physics is collapsing towards a homocentric view of the Universe, but Hawking is, of course, quite wrong about there not being an Observer all along.

MORE:
SWIMMING TO PRIMORDIA:
Robert Wright interviews Brian Swimme on cosmic evolution (Slate)

Brian Swimme is a mathematical cosmologist on the graduate faculty of the California Institute of Integral Studies in San Francisco. [...]

Wright: And and and this this gets at a question I have... now you definitely with this story you want to do some things that religion has traditionally done, orient people, inform their values and so on... one thing a lot of religions have done is give people a sense that things were meant to be you know... there was a God that designed the universe or there were some supernatural order that imbues their own life with purpose. And there, as I read you, you are kind of teetering on the edge of that but not quite doing it. Right?

Brian Swimme: Yes. That's right. Teetering is not a word I'd use but it would certainly... there I guess it's trying so hard to get a feel for the way in which there is a random dimension to the universe without question.

Wright: Let me give you let me give you an example ...

Brian Swimme: Yes.

Wright: ... of you talk in "The Universe Story" about several kind of parameters of the universe that were just quite exquisitely fortuitous from our point of view. If they had been off a little in either direction, things would have collapsed, life could have been impossible or something. Here's just one example, you're talking about the curvature of space time which I can't quite imagine clearly but anyway ... the curvature of space time: "Had the curvature been a fraction larger the universe would have immediately collapsed down into a massive black hole. Had it been a fraction smaller the universe would had exploded into a scattering of lifeless particles. Thus the curvature of the universe is sufficiently closed to maintain a coherence of it's various components and sufficiently open to allow for a continued creativity." Now a lot of other you know...

Brian Swimme: Yes. Yes.

Wright: ...gravitational constant whatever I don't know if you mention that one but there are various things you do mention...

Brian Swimme: Right.

0:09:27.000

Wright: Now some people conventionally religious people have looked at these things and have said clearly the universe was designed for a purpose it's just too good to be true. What's what's your view on that?

Brian Swimme: Well I guess first of all it'd be the word design because as soon as you use the word design at least for me it then you're talking about a designer and so you have you have someone sort of outside the universe, Newton's idea was tinkering with it so you set the universe and kind of run run and tinker with it but I think what is what word discovers something way more exciting that is that universe is finding it's way, the universe is you know probing and exploring and it is from the beginning it's it's in search of something. Now I mean that I'm personifying by using that...

Wright: Yes.

Brian Swimme: ... and that is that does make it hard I think...

Wright: Well but how literally do you mean the the personification. I mean is the you know... you do think the universe is a living system?

Brian Swimme: Yes.

Wright: And now living systems do have purposes though in the sense I mean even evolutionary biologists would say that an animal you can say is "designed by natural selection" and that's why it pursues goals like getting it's genes into the next generation and and and and goals that are subordinate to that I mean when we think of a living system we think of something that is the result of at least a process of design even if it's a kind of impersonal process like natural selection and something that has it's own little set of goals, right?

Brian Swimme: Yes.

Wright: Is that what you mean to imply?

Brian Swimme: I do...

Wright: About... you do? So the universe does have a purpose.

Brian Swimme: I would not call it it's own little set of goals.

Wright: No. Well if it's the universe it's big goals. Obviously.

Brian Swimme: Yes. I think that the universe does have purpose it does have direction in the sense that but they're not in my own way of thinking they're not fully formed. There are I think something like, go back early in the universe, I think there are literally an infinite of things that are possible but out of all those universe is always striving to give birth to the to the richness that's there potentially that'd be one way of how I'd talk about it so that it it could be that the universe would be very very different than it is right now, but it would still have something like life and something like a kind of rich inner-connected world of our planet. That'd be how I'd look at it. Those those those aims are present somehow, darkly, and then how are they present? Well. I don't know. I mean, we just found this out. We just discovered all this.

0:12:32.000

Wright: You mean by "all this" you mean?

Brian Swimme: I mean the the discovery of the big bang cosmology...

Wright: Right.

Brian Swimme: ... is extremely recent. We've been humans for 150,000 years.

Wright: Right.

Brian Swimme: And now just just just like yesterday we discovered some of the details of this happening we call the universe and so I it's going to take us time to to sort out really what's going on. When... to talk about designers... I think I think that's unfortunately collapsing back into a previous way of thinking that isn't... it's more exciting than that.

Wright: But but purpose is a word you are willing...

Brian Swimme: Yes.

Wright: ... to use.

Brian Swimme: Yes I am.

Wright: So the universe has a purpose?

Brian Swimme: Yes.

Wright: And you don't exactly what it is but you got a feeling that sentient life is part of the point.

Brian Swimme: Yes. Yes I do. Right. Sentient life and and and display of all kinds of energy constellations. So that the universe starts off so simple really in terms of of of it's structure and yet over time it just it throws out all this exotic stuff. So I think that is part of one of the main aims of the universe...

Wright: To display...

Brian Swimme: Yes...

Wright: ... beautiful stuff...

Brian Swimme: Yes.

Wright: But there wouldn't be much point in displaying beautiful stuff if there weren't creatures capable of apprehending beautiful stuff. I mean who is it showing off for?

Brian Swimme: Well, that's a good question. But it may it may just that alone may be what the universe is about... it doesn't happen without...

0:14:20.000

Wright: This is kind of it reminds me of kind of Whitehead a little bit.

Brian Swimme: Oh yes I would say that the three thinkers...

Wright: He was a process theologian, right?

Brian Swimme: Process... yes.

Wright: And and and do you have a good thumbnail definition of that or should we pass over that? What what what does process theology mean?

Brian Swimme: He would be a he would be a you know the first process thinker that gave birth to process theology. He was really doing cosmology. And his his I give you here's a thumbnail sketch of Whitehead... His idea was that we have in science exhausted the mechanistic metaphor and it it took us places but it was it was no longer viable in terms of what we learned but especially the quantum world so he was attempting to give a framework for understanding the universe with organism as the fundamental concept not machine. That would be one way to think about it. And then his idea of organism would be that that the fundamental reality of the universe is an experience in subject so his phrase is outside of experiencing subjects there's nothing nothing just bright nothingness. So not only would ... he would say it's not just display but it's the richness the intensity of the experience that would be what the universe is aiming at.

0:15:42.000

Wright: Ok. The so really I'm a little surprised because you're being more explicit than I think you generally are in your writing about the idea that the universe has a purpose. Maybe I mean I haven't read every word you've written but but but I'm a little surprised and what I was going to ask you was isn't this one thing that religions have traditionally done that you're world view doesn't do... that is to say by suggesting an over-arching purpose imbue people lives with a meaning from beyond in some sense... I mean would you say your world view has a transcendent source of meaning in it?

Brian Swimme: You see when you words like beyond then I start to loose my confidence because I'm really working out of primarily the scientific data so also like the word beyond or also transcendence I get a little bit uneasy...


Because his story has melded seemlessly into the One Story.


[originally posted: 4/25/06]

Posted by Orrin Judd at January 19, 2010 4:29 PM
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