George Ellis: spacetime is growing & there's no global wave function for a multiverse

[C C]

George Ellis was one of Stephen Hawking's co-authors. He apparently subscribes to his own version of the GBU called the "Evolving Block Universe". While he believes that wave functions are real like Roger Penrose does, he dismisses the idea of a global wave function. Even rejecting a WF corresponding to smaller macroscopic objects like cats and brains.

If time was both structurally existential and endless, then that would seemingly demand a GBU model because infinity is not a completed situation or quantity. However, the existing "past" of a GBU would still be akin to the conventional block universe, and there's no guarantee that we're actually at the growing edge. We could be spatiotemporally located anywhere from minutes to billions of years behind it. Since the standard BU has its own cognitive explanation for the experience of "moving" along it from one different state to the next, that would still apply in the GBU, too. (The appearance of time passing isn't solely dependent on being at the edge of the "magically" enlarging block.)

Debate over the physics of time (George Ellis segment)
https://www.quantamagazine.org/a-debate-...-20160719/

For George Ellis, a cosmologist at the University of Cape Town in South Africa, time is a more basic entity, one that can be understood by picturing the block universe as itself evolving. In his “evolving block universe”model, the universe is a growing volume of space-time. The surface of this volume can be thought of as the present moment. The surface represents the instant where “the indefiniteness of the future changes to the definiteness of the past,” as he described it.

“Space-time itself is growing as time passes.” One can discern the direction of time by looking at which part of the universe is fixed (the past) and which is changing (the future). Although some colleagues disagree, Ellis stresses that the model is a modification, not a radical overhaul, of the standard view.

“This is a block universe with dynamics covered by the general-relativity field equations — absolutely standard — but with a future boundary that is the ever-changing present,” he said. In this view, while the past is fixed and unchangeable, the future is open. The model “obviously represents the passing of time in a more satisfactory way than the usual block universe,” he said.

Unlike the traditional block view, Ellis’s picture appears to describe a universe with an open future — seemingly in conflict with a law-governed universe in which past physical states dictate future states. (Although quantum uncertainty, as Ellis pointed out, may be enough to sink such a deterministic view.) At the conference, someone asked Ellis if, given enough information about the physics of a sphere of a certain radius centered on the British Midlands in early June, one could have predicted the result of the Brexit vote. “Not using physics,” Ellis replied. For that, he said, we’d need a better understanding of how minds work.

SPOILER SNIPPET: Ellis stresses that the model is a modification, not a radical overhaul, of the standard view. “This is a block universe with dynamics covered by the general-relativity field equations — absolutely standard — but with a future boundary that is the ever-changing present,” he said.
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CURT JAIMUNGAL (joined by Ellis)
https://youtu.be/wnpYBg008AQ

VIDEO EXCERPTS: We do not live in a block universe, we evolve in an evolving block universe. [...] So my model of the universe is an evolving block universe. In another billion years, that right-hand edge will have moved to the right a billion years. Space-time itself would have grown, space-time would have gotten bigger. And how will that have happened? Well, through the Einstein field equations.

[...] I agree with Roger Penrose that wave function collapse is real, and with my colleague Barbara Drossel I've written papers about what we call contextual wave function collapse. That wave function collapse is real, but the way it happens is always determined by the context, and we give a very detailed example of that in our paper called "Contextual Wave Function Collapse."

So it's an objective collapse theory?

Yeah.

[...] Now, the real universe is not linear, so there's a paradox there. How does nonlinear stuff come out of a totally linear equation? They try to say, "well, it comes from the multiverse."

Well, the real solution comes from looking back to general relativity. The great breakthrough in general relativity occurred when we discovered the concept of coordinate systems. You can't cover an ordinary space-time by a single coordinate system. You have to have a whole atlas of coordinates, and it's the atlas which covers space-time, not a single one, and that's what enabled us to discover all the topological results in general relativity.

Now, what I claim is exactly the same holds in quantum physics. There is no global wave function — that's a fantasy. There are local wave functions everywhere, and the local wave functions cover the whole space-time, but there is no single wave function for a universe, which completely undercuts the whole idea of the quantum multiverse.

There's no wave function for a cat and all that stuff. There's no wave function for a brain. And the idea that one single wave function could encompass a whole brain is purely fantasy. It's obviously nonsense because the key fact of quantum physics is that quantum physics equations are linear.

[...] You think the multiverse is nonsense?

Okay, there are various kinds of multiverses. [...] I'm prepared to believe that some chaotic cosmologies [cosmological inflation] will lead to different expanding universe domains. I'm prepared to believe that. but I'm not an expert in inflationary theory...

Hawking's co-author: "No global wave function" ... https://youtu.be/wnpYBg008AQ

https://www.youtube-nocookie.com/embed/wnpYBg008AQ