Spacetime is doomed

[atanu]

Spacetime is doomed.

The Doom of Spacetime - Why It Must Dissolve Into More Fundamental Structures - Nima Arkani-Hamed

What will will replace it? Let the imagination run riot. I will sit with a big chicken fry bucket.

 

[viole]

Spacetime is doomed.

The Doom of Spacetime - Why It Must Dissolve Into More Fundamental Structures - Nima Arkani-Hamed

What will will replace it? Let the imagination run riot. I will sit with a big chicken fry bucket.

When will that happen? And what reference frame are they using to measure that?

Ciao

- viole

 

[ChristineM]

Spacetime is doomed.

The Doom of Spacetime - Why It Must Dissolve Into More Fundamental Structures - Nima Arkani-Hamed

What will will replace it? Let the imagination run riot. I will sit with a big chicken fry bucket.

One of 2 scenarios.

The universe will continue on its merry way, inflating so each particle becomes further and further away until the point that they are too far from each other and expanding so rapidly that the speed of light effectively looses our universe. Estimated time about 15 trillion years

Or

Stars will burn out and collapse,the bigger ones forming black holes which devour the remnants of the smaller stars. Eventually the universe is only black holes. And as black holes will, they will evaporate to nothing. Estimated time about 100 trillion years

How long before space time disolves.

Edit, there may be more than 2 scenarios but my brain isnt big enough to imagine them

 

[Polymath257]

Spacetime is doomed.

The Doom of Spacetime - Why It Must Dissolve Into More Fundamental Structures - Nima Arkani-Hamed

What will will replace it? Let the imagination run riot. I will sit with a big chicken fry bucket.

There *is* a fundamental question as to whether it even makes sense to talk about spacetime geometry at the Planck level.

My personal bet is that something along the line of non-commutative geometry is going to be the best way forward, but that is merely a wild guess on my part.

It's a bit difficult to explain the differences between normal geometry and non-commutative geometry, but the essence is that nearby points have an uncertainty relationship between them. This gives a fundamental size which limits how small it even makes sense to talk about something being. The same would, of course, happen for time as well.

The reason I am inclined in this direction is that non-commutative geometry is based on the same sort of 'operators on Hilbert space' as quantum mechanics already is. This allows both a generalization of QM and or GR as well as dealing with the issues of geometry at the Planck level.

 

[The Hammer]

Spacetime is doomed.

The Doom of Spacetime - Why It Must Dissolve Into More Fundamental Structures - Nima Arkani-Hamed

What will will replace it? Let the imagination run riot. I will sit with a big chicken fry bucket.

What are the philosophical implications of this 'dissolution' of spacetime?

 

[atanu]

What are the philosophical implications of this 'dissolution' of spacetime?

One may be tempted to let imagination fly. So, let the experts speak. The following article in Nature finishes with:
What Is Spacetime?

In physics and, more generally, in the natural sciences, space and time are the foundation of all theories. Yet we never see spacetime directly. Rather we infer its existence from our everyday experience. We assume that the most economical account of the phenomena we see is some mechanism that operates within spacetime. But the bottom-line lesson of quantum gravity is that not all phenomena neatly fit within spacetime. Physicists will need to find some new foundational structure, and when they do, they will have completed the revolution that began just more than a century ago with Einstein.
​

Donald Hoffman notes:
Edge.org

The standard assumption in perceptual psychology is that evolution favors veridical perceptions, those that accurately describe those aspects of the environment that are crucial to the fitness of an organism. It is not standard to assume that the very space-time format of our perceptions is itself non-veridical, primitive and illusory. How will this field have to change if space and time are themselves illusions? And how will our notions of physical causality have to change? Will these changes affect how we approach the classic mind-body problem, the question of how our conscious experiences are related to our physical bodies and, in particular, to the activity of our brains?​

Or as Arkani says:

“We’re not building a machine that calculates answers, instead, we’re discovering questions. Nature’s shape-shifting laws seem to be the answer to an unknown mathematical question”.​

So, Arkani feels that even the question is unknown.

 

[Nakosis]

Spacetime is doomed.

The Doom of Spacetime - Why It Must Dissolve Into More Fundamental Structures - Nima Arkani-Hamed

What will will replace it? Let the imagination run riot. I will sit with a big chicken fry bucket.

I think the question would be whether physical theories could continue to exist without spacetime. Could new theories be developed which predict the phenomenon we observe not using spacetime?

 

[atanu]

There *is* a fundamental question as to whether it even makes sense to talk about spacetime geometry at the Planck level.

My personal bet is that something along the line of non-commutative geometry is going to be the best way forward, but that is merely a wild guess on my part.

It's a bit difficult to explain the differences between normal geometry and non-commutative geometry, but the essence is that nearby points have an uncertainty relationship between them. This gives a fundamental size which limits how small it even makes sense to talk about something being. The same would, of course, happen for time as well.

The reason I am inclined in this direction is that non-commutative geometry is based on the same sort of 'operators on Hilbert space' as quantum mechanics already is. This allows both a generalization of QM and or GR as well as dealing with the issues of geometry at the Planck level.

Both GR and QM are inapplicable at Planck level, so I am not sure that non-communicative geometry will be of much use. But I am not knowledgeable about this.

At least space time is experiential. What else is experiential and fundamental?

 

[atanu]

I think the question would be whether physical theories could continue to exist without spacetime. Could new theories be developed which predict the phenomenon we observe not using spacetime?

Whatever new comes up will surely have space time as a product.

 

[atanu]

Now physicists seem to have proven that black holes can shed information, which is impossible by definition.

https://www.quantamagazine.org/the-...XqRPktIVZF5q-IcehGNX1UH1Fgx6dZwp14zeK4pivnntM

The gravity of a black hole is not so intense after all that nothing can escape it. Information does escape.

The work is highly mathematical and strings together wormholes, the holographic principle, emergent space-time, quantum entanglement, and quantum computers. Due to rawness of the work and due to its complexity many are not convinced. Most physicists, however, appear to agree that space-time itself seems to fall apart at a black hole, implying that space-time is not the root level of reality, but an emergent structure from something deeper that is not temporal or spatial.

...

 

[Polymath257]

Now physicists seem to have proven that black holes can shed information, which is impossible by definition.

https://www.quantamagazine.org/the-...XqRPktIVZF5q-IcehGNX1UH1Fgx6dZwp14zeK4pivnntM

The gravity of a black hole is not so intense after all that nothing can escape it. Information does escape.

The work is highly mathematical and strings together wormholes, the holographic principle, emergent space-time, quantum entanglement, and quantum computers. Due to rawness of the work and due to its complexity many are not convinced. Most physicists, however, appear to agree that space-time itself seems to fall apart at a black hole, implying that space-time is not the root level of reality, but an emergent structure from something deeper that is not temporal or spatial.

...

Another aspect of this is that it is based on a mathematical *model* which has not been tested.

 

[Twilight Hue]

One of 2 scenarios.

The universe will continue on its merry way, inflating so each particle becomes further and further away until the point that they are too far from each other and expanding so rapidly that the speed of light effectively looses our universe. Estimated time about 15 trillion years

Or

Stars will burn out and collapse,the bigger ones forming black holes which devour the remnants of the smaller stars. Eventually the universe is only black holes. And as black holes will, they will evaporate to nothing. Estimated time about 100 trillion years

How long before space time disolves.

Edit, there may be more than 2 scenarios but my brain isnt big enough to imagine them

Who says black holes dissolve into nothing?

 

[ChristineM]

Who says black holes dissolve into nothing?

Steven Hawking for one

 

[Polymath257]

Who says black holes dissolve into nothing?

That is one of the consistent predictions of what is known about quantum gravity.

It is not, however, verified by observation.

 

[shunyadragon]

Spacetime is doomed.

The Doom of Spacetime - Why It Must Dissolve Into More Fundamental Structures - Nima Arkani-Hamed

What will will replace it? Let the imagination run riot. I will sit with a big chicken fry bucket.

Eventually more fundamental structures (?). That is how science works.

That big buck of fried chicken won't help you, but your waist may benefit.

 

[Brickjectivity]

Spacetime is doomed.

The Doom of Spacetime - Why It Must Dissolve Into More Fundamental Structures - Nima Arkani-Hamed

What will will replace it? Let the imagination run riot. I will sit with a big chicken fry bucket.

I think I will wait until there is more consistent agreement. Some of these cutting edge ideas are interesting. They are still banging things together in colliders, so I will stay tuned. They haven't incontrovertibly explained what is causing the expansion, and astronomers are still investigating that.

They haven't explained the cause of expansion, so I can come up with a counter idea. There could be *some* invisible link between all matter that requires a mediated distance such that if some matter is compressed it causes all other matter to tend to disperse on a cosmic scale. This is just a random idea I'm coming up with, but their theory is so vulnerable. They haven't established anything. Suppose that the expansion of the universe is driven by the compression of matter in black holes? That would make the expansion slow down and stop when the black holes stopped feeding. There I have made a vague possible explanation that could mean that the expansion will stop. I can do that because they can't fully explain what is causing the expansion, and since they haven't fully explained what is causing the expansion they cannot say that spacetime must dissolve. It is a conjecture.

 

[Miken]

I have always had a problem with the alleged loss of information inside a back hole. Yes, I have read Hawking’s papers on the subject of black holes and what is more I understand them. The problem I see is that to a distant observer (one far enough away to avoid capture) nothing ever actually enters the black hole. Objects falling toward the event horizon are seen to be increasingly time dilated. The time dilation is so extreme near the event horizon that, to a distant observer, it would take an infinite amount of time for a falling object to reach the event horizon. This result derives from exactly the same mathematics that points to the existence of an event horizon.

For a distant observer (like us) there is no loss of information into a black hole. It is all still there outside the event horizon and will be for an infinite amount of time.

Note that to an observer falling into a black hole it will take only a finite amount of time to get gobbled up by crossing the event horizon. Time dilation resulting from acceleration is not noticeable to the accelerating observer. Rather it appears to that observer that the acceleration continues beyond the speed of light without limit as judged by how quickly fixed markers would go past as measured by that observer’s clock. That is a different matter.

The various mathematical treatments of evaporation of a black hole deal with timeframes relative to the event horizon. However, to a distant observer the evaporation process and its resulting photons will not be observable until an infinite amount of time has passed due to the extreme time dilation factor.

We already know that both Quantum Theory and General Relativity are not the end of the road. QT cannot deal with gravity and GR is classical, not quantized as we know physical reality is. What solutions might be developed in the future to give a clearer picture of what happens with a black hole is mere speculation at this point although M-Theory looks very interesting. But let us not forget that Supersymmetry looked very interesting until the LHC demonstrated that at least the less convoluted (and more credible) forms of Supersymmetry do not hold up. The predicted particles are just not there.

 

[Miken]

The brief summary given in the minutes linked by the OP is a serious misrepresentation of what Arkani-Hamed really said. I could not imagine that a theoretical physicist of his caliber would ever say such things. I had to track down a transcript of his presentation, which naturally says things that are much more reasonable.

First, to get this out of the way. Arkani-Hamed did not say that space and time are going to disappear. He said that our present concepts of them are inadequate and will need to be replaced. Nor does the summary linked by the OP say anything like that.

From the OP link.

Arkani-Hamed then described the two “storm clouds” he sees for spacetime and quantum mechanics. The first storm cloud suggests that spacetime is doomed. The second, that quantum mechanics are limited.

To explain the first cloud, Arkani-Hamed presented a thought experiment. To see what exactly is going on at arbitrarily small distances, we must use high energies. In a world without gravity, there is, in principle, no limit to scaling the size of the detector to see what is going on at increasingly small distances. But we live with gravity, and where there is too much mass, we get a black hole that traps light – meaning that if we build too big a detector, we will create a black hole that will prevent us from seeing what happens at the smallest distances. Thus, gravity limits our ability to measure spacetime, which means our current understanding of spacetime is merely approximate and not fully accurate.

What was really said has nothing to do with the mass of the accelerator and the effect of gravity on it. The limitation is that ultimately the energy density produced in an accelerator would be sufficient to create a black hole, preventing the usual shower of particles and energy that is examined for interesting stuff. This puts a limit on how deeply we can probe.

Again from the OP link.

Similarly, the second cloud is explained by the problem of measuring quantum mechanics. To measure such quantum observables, our precision improves by how many measurements we take. But, to take the infinitely many measurements required to reach almost exact precision, would require an infinitely large measuring apparatus, which is again limited by gravity. This limitation means quantum mechanics is also an approximation.

This is simply totally different from anything Arkani-Hamed said. It has nothing to do with the size of the measuring device. There is a fundamental limit to the accuracy of observations due to the Heisenberg Uncertainty Principle. Repeated measurements are not going to get around that. You cannot simultaneously and accurately measure two complementary variables (OK that is really Bohr complementarity). You can make both measurements as precise as you want. That is, the needle on the gauge does not quiver to use a metaphor.) But on subsequent observations you will realize that the answer you expected is wrong.

Arkani-Hamed also delved into interesting subjects, such as vacuum energy, rolled up dimensions, the expansion of the universe and others, that are not represented in the brief summary in the OP linked minutes.

 

[atanu]

The brief summary given in the minutes linked by the OP is a serious misrepresentation of what Arkani-Hamed really said. I could not imagine that a theoretical physicist of his caliber would ever say such things. I had to track down a transcript of his presentation, which naturally says things that are much more reasonable.

First, to get this out of the way. Arkani-Hamed did not say that space and time are going to disappear. He said that our present concepts of them are inadequate and will need to be replaced. Nor does the summary linked by the OP say anything like that.

From the OP link.

What was really said has nothing to do with the mass of the accelerator and the effect of gravity on it. The limitation is that ultimately the energy density produced in an accelerator would be sufficient to create a black hole, preventing the usual shower of particles and energy that is examined for interesting stuff. This puts a limit on how deeply we can probe.

Again from the OP link.



This is simply totally different from anything Arkani-Hamed said. It has nothing to do with the size of the measuring device. There is a fundamental limit to the accuracy of observations due to the Heisenberg Uncertainty Principle. Repeated measurements are not going to get around that. You cannot simultaneously and accurately measure two complementary variables (OK that is really Bohr complementarity). You can make both measurements as precise as you want. That is, the needle on the gauge does not quiver to use a metaphor.) But on subsequent observations you will realize that the answer you expected is wrong.

Arkani-Hamed also delved into interesting subjects, such as vacuum energy, rolled up dimensions, the expansion of the universe and others, that are not represented in the brief summary in the OP linked minutes.

The OP links to the minutes of the meeting. I will read again to try to understand what you are saying.

But are you contesting the main point that Spacetime is not the fundamental structure?

 

[atanu]

I think I will wait until there is more consistent agreement. Some of these cutting edge ideas are interesting. They are still banging things together in colliders, so I will stay tuned. They haven't incontrovertibly explained what is causing the expansion, and astronomers are still investigating that.

They haven't explained the cause of expansion, so I can come up with a counter idea. There could be *some* invisible link between all matter that requires a mediated distance such that if some matter is compressed it causes all other matter to tend to disperse on a cosmic scale. This is just a random idea I'm coming up with, but their theory is so vulnerable. They haven't established anything. Suppose that the expansion of the universe is driven by the compression of matter in black holes? That would make the expansion slow down and stop when the black holes stopped feeding. There I have made a vague possible explanation that could mean that the expansion will stop. I can do that because they can't fully explain what is causing the expansion, and since they haven't fully explained what is causing the expansion they cannot say that spacetime must dissolve. It is a conjecture.

I will require several reading to understand it. Let me try.