15 ms·

Rebuilding Quantum Theory From Simple Physical Principles

69 points by behoove 9y ago

dboreham 9y ago
Reading this I see for the first time why the notion that the universe is a simulation isn't so far fetched.
- macawfish 9y ago
  Maybe you'd enjoy John Lilly's book "simulations of god". It's a meditation on human attempts to grasp life and existence.
- deleted 9y ago
  [deleted]
- danbruc 9y ago
  I have to disagree and I can not really understand what is so appealing about the simulation idea to many. It is an idea that will lead nowhere because you are unable to distinguish a real universe from a simulated one. In order to do this you would have to know what at least one of those scenarios looks like and then compare the universe you observe to what you know to be true about a real or simulated universe. It is common to base such thoughts on analogies between our universe and our computers, i.e. our computers have only finite precision while the universe seems continuous, at least to a very good approximation. Therefore if we would detect rounding errors in the universe we would know that the universe is actually a simulation. But that is at least naive and most likely not true. How would you know that a real universe does not have finite precision? Why would you assume simulation must have finite precision? And you have to answer the same question for any other feature you want to use to make the distinction.
  - QAPereo 9y ago
    I have to disagree and I can not really understand what is so appealing about the simulation idea to many. You can’t see the appeal of an unfalsifiable conjecture that everything including us, is an intentional creation of some manner of vast and powerful intelligence? Aliens, Simulators, Bulk Beings, or you know... Gods. It’s just new window dressing on an ancient dream.
    - danbruc 9y ago
      Well, I can neither see the appeal of gods. I guess many people just like to have uncertainty removed from their life even if that is not actually true. And that is probably the point that I don't get, why or how people get something out of those, well let me call them lies.
      - QAPereo 9y ago
        The universe is big and scary, and decidedly not anthropocentric or even comprehensible,.. some people want it to be, decide that it is, and believe that.
    - chr1 9y ago
      The question "whether we live in simulation" is indeed a new dressing. But the question "is simulation possible, and if yes what it can look like" is new, and can have useful answers.
      - QAPereo 9y ago
        But the question "is simulation possible, and if yes what it can look like" is new, and can have useful answers. That is pretty interesting, but now how most people formulate the issue. After all, what we could simulate, or what could be simulated in a universe like ours, in principle is pretty interesting. The question of what another reality simulating us would be like isn't, because it could be absolutely anything at all. Questions without the hope of answers are, to me at least, not interesting.
        chr1 9y ago
        True, if we go specifically searching for the answer to the second question, we may not find much interesting, but when we know more about the first question we can gain some insights about the second one. So if by not interesting you mean `this door is closed now, revisit later` i completely agree with you!
  - indubitable 9y ago
    Personally I find the peculiar implication of a simple question so appealing. Will we eventually be able to create simulations that one would be unable to differentiate from reality if that simulation is all they had ever known? The answer there is quite self evident, yet it simultaneously somehow implies it is highly likely that we are ourselves within a simulation. The reason is that we can safely assume that we are within one of n + 1 realities. The n simulated realities and the 1 real reality. Unless you attribute some sort of exceptionalism bordering on creationism to our existence, there's every reason to think that n is going to proportional to the number of advanced civilizations in existence and is presumably going to be very very large. And as you increase n the odds of us actually being in the 'real' reality, which are of course just 1/(n+1), approach 0. Like you mention it's something that doesn't necessarily go anywhere. Even if you "prove" it after death, that life you'd be experiencing at that point faces the same logical issue - at least unless the argument loses consistency at some point. Something most seem reluctant to admit is that it's also comforting as an atheist. I always expected the infinity of time after my existence to be very much akin to the infinity of time before my existence. That's just disappointing. The seemingly high probability that all is not as it seems is certainly emotionally appealing. But it's certainly not just the emotional appeal driving me there - I could obviously have chosen to invoke Pascal's Wager in the decades of time prior to considering this, but it seemed fake -- this, somehow, does not. It also answers, or at least compellingly kicks the can, of the question of existence. If I write a program to spit out a random number, I presume that there is no entity that suddenly whisks into existence under the false impression that it is choosing a random number - which it then decides upon, before then being whisked out of existence. So why am I, the 'thing' spectating the outcome of the series of chemical and electrical reactions carried out by this body, here? Descartes would have quite the time if the answer to our little question had been yes during his time. It changes the picture so much more than the dreams that drove his ponderances. --- From a scientific point of view, it's obviously not a great concept as it cannot be falsified. And like you mention, it also cannot really be physically proven without begging the question. On the other hand, it can be treated as a soft science and if a preponderance of evidence does lean towards supporting it then we can at least say, "Hmm.. well we can't really say anything for certain, but that's certainly interesting."
    - 9y ago
  - elorant 9y ago
    It is appealing for three reasons. 1) As computer engineers we understand it's doable. Give it a couple of centuries and our civilization could reach a computing capacity to simulate the entire observable universe 2) A lot of things just don't make sense. Like consciousness for example. We can't define it, and we don't even know it it's real. If you take consciousness out of the equation humans are just laborious software. 3) This is objective of course, but quite a lot of people are experiencing coincidences that seem unreal. That sounds metaphysics and most of us wouldn't touch it with a barge pole but from a simulation perspective makes total sense. Oh and it makes a lot of people uncomfortable. For me it's one of the best ways to test someone's intellect. You bring it into a conversation and people start feeling unease.
    - andrepd 9y ago
      > Give it a couple of centuries and our civilization could reach a computing capacity to simulate the entire observable universe This is not even remotely true, not even if a perfect Moore's law were to continue for thousands of years. Man, we're hard pressed to even simulate single molecules. > quite a lot of people are experiencing coincidences that seem unreal Oh come on x) "Coincidences" are psychological illusions and misatribution biases at work, not the work of an intelligence behind our universe. This is the "I prayed to god and my back pain healed; it's a miracle" type of thinking.
    - danbruc 9y ago
      As computer engineers we understand it's doable. Give it a couple of centuries and our civilization could reach a computing capacity to simulate the entire observable universe This seems at the very least questionable. Why do you think you can simulate the entire universe just using a tiny fraction of the resources of the universe? It seems to me that could only work if the universe were highly compressible and I don't see any obvious evidence for that. And even then I think it could not work because if the universe is in some sense redundant and could be compressed then it actually provides less resources to work with than if it would not have those redundancies. Take as an analogy for the later two processors executing the same code in lockstep as it is sometimes done for redundancy in safety critical systems. You can mostly get away with only simulating one of the processors but you essentially also only have one processor to work with. And while you can probably simulate the processors on the processors the simulation will probably be at least ten times slower than the actual processor if you only want to use one tenth of the available resources, i.e. clock cycles. And finally memory will be a real problem because you only have as much memory available as you want to simulate.
  - gilbetron 9y ago
    Why are you unable to distinguish it? It is not, a priori, impossible. It is entirely possible that there may be ways to determine if we are in a simulation, depending on how the simulation is done. No simulation is perfect, and it is theoretical feasible to find the imperfections.
    - danbruc 9y ago
      To look for imperfections in a simulation requires knowing what the real thing actually looks like. If our universe is a simulation, where do you get the knowledge from what a real universe looks like?
      - chr1 9y ago
        You can look for contradictions, inconsistencies or for macro scale phenomena not explainable by micro scale laws.
        danbruc 9y ago
        That doesn't work. The rules used by the simulator could just be the rules of the real universe, you can not tell the difference. Or to put in programming terms, you are given an object x to inspect, our universe, and you have to decide whether it is an instance of class RealUniverse or an instance of class SimulatedUniverse but you have no knowledge of what any of those classes looks or behaves like.
        gilbetron 9y ago
        You seem to be arguing that it isn't always possible to detect you are in a simulation, whereas the rest of us are arguing that it could be possible in some simulations.
        jamesrcole 9y ago
        I think they're arguing that whatever evidence you think you've found for it being a simulation could always just be how the universe is.
  - breatheoften 9y ago
    Maybe its an acknowledgement of something about the nature of abstraction from observation. Perhaps the true universe is and always be a simulation error away from observation -- under such a hypothesis, science will be an eternal process of finding details in our understanding which are actually accidental results of the simulation capacity of our current understanding, then figuring out how to remove the flaw, and then peaking behind the next curtain ...
  - WhitneyLand 9y ago
    You have basically said it may be unprovable. First, that may be true, but it also may not be true. Secondly even if it were true, why would that change anyone’s interest or curiosity about it being a possibility?
    - danbruc 9y ago
      It's nothing special about the simulation idea, there are many similar things. Solipsism, only your mind is real and the outside world may or does not exist. Last Thursdayism, the universe came into existence last Thursday in the exact state of last Thursday, before that there was nothing or something very different. They all share roughly the same idea, there is some reality but by some perfect arrangement of smoke and mirrors you are by definition unable to ever learn something about that reality. There is certainly some value in discussing those ideas on a meta level, finding common characteristics, figuring out limits, but beyond this the individual ideas are, at least in my opinion, mostly a waste of time. What is the point of analyzing something that by definition leaves you stuck? And as far as I can tell philosophy has long ago mostly accepted this and made it something like an axiom that there is an reality and we can learn about it and doesn't concern itself much anymore with ideas that would, if true, block any possible progress.
  - dboreham 9y ago
    I'm not sure if the idea appeals to me or not: I was more saying "I've heard Elon and co talking about this and just assumed it was like they'd seen The Matrix again on Netflix...". But reading this article (late, I guess..) the penny dropped when I saw ideas like the boundary conditions are the maximum information density of particles, and the upper bound to information celerity. Starts to sound like the kind of limitations you'd have if you built a huuuugge simulator.
- goalieca 9y ago
  The article states that axioms they are using for the reconstruction theory end up being abstracted above the underlying reality. It does not suggest the underlying reality is many-worlds, simulation, etc.
- charlesism 9y ago
  I don't understand what the difference between a "real" and a "simulated" universe would be. It's probably just a word game to make a distinction.
bigtimber 9y ago
Fyi, the topic was discussed a few months back in https://news.ycombinator.com/item?id=15163528 https://news.ycombinator.com/item?id=15163528 after the _Quantamagazine_ article was reprinted in _Wired_.
amelius 9y ago
Any role for Pilot Wave Theory here? https://www.quantamagazine.org/pilot-wave-theory-gains-experimental-support-20160516/ https://www.quantamagazine.org/pilot-wave-theory-gains-exper... > An experiment claims to have invalidated a decades-old criticism against pilot-wave theory, an alternative formulation of quantum mechanics that avoids the most baffling features of the subatomic universe.
wruza 9y ago
After familiarizing with QM/SR concepts some years ago, I came to the conclusion that there is nothing more strange and pointless than the world without these two. If max speed was infinite (or finite but non-relative, which is essentially the same) and there was no probabilistic outcomes, then the world would "happen to the end" instantly and/or with analytically predefined series of events. From any initial state. The entire "consequence" concept would fall apart. There is no point for the universe to exist in classical & atomic-ball electron mode. Idk why both seem so unnatural to so many people who try to get what it means; it feels like it should be obvious instead - it means evolving existence, the only thing you're able to appear in and think about it. Classical uniform fundamental time is much stranger to me than what emerges from what we have now; we simply shifted our focus to "oh" forgetting how much "wtf" was left behind. I'm not claiming any deep-enough physics or math knowledge (layman actually), consider it a funny philosophical view.
- chr1 9y ago
  > with analytically predefined series of events. This doesn't make universe less interesting or more predictable. Consider Mandelbrots set, it is fully analytically predefined, but only way to find it's details is to perform the whole calculation. Similarly the universe can be predefined, but the only way of finding its state after some amount of time can be performing a calculation fully equivalent to letting the universe to live for that time.
  - wruza 9y ago
    >amount of time can be performing a calculation fully equivalent to letting the universe to live for that time This one is very interesting since it brings back the question what time really is. Your point involves “metacircular” observer that can only work/simulate as fast as it can, but the definition of “fast” is external to it. Sure, if we simulate predefined-but-calc-required in our universe, then it will take time. But why should we measure it this way? I mean, does calculation process exist at all without something that requires time for it? [Or we’re really talking about the same fundamental thing that lies behind both our and hypothetically deterministic universe.]
platz 9y ago
> Wins Neutrinos aren't massless Confirmed higgs > Problems Hierarchy problem Fine tuning Why is the cosmological constant so "wrong compared to theory" No evidence for supersymmetry yet at 10^-17cm via LHC No evidence for WIMPs How do we combine QM + GR? Do black holes destroy information? How to solve the BH firewall problem? > Speculation Is there supersymmetry at higher energies than the LHC can probe? Is spacetime doomed? I.e. is space-time a hologram on the boundary or some other emergent phenomenon Is there a multiverse? Is decoherence a solution, or does the wave function "collapse", or simply many-worlds? Is perturbation theory sensible or is there a deeper more elegant way to calculate scattering? Is time emergent or fundamental?

69 points by behoove 9y ago

dboreham 9y ago

Reading this I see for the first time why the notion that the universe is a simulation isn't so far fetched.

macawfish 9y ago
Maybe you'd enjoy John Lilly's book "simulations of god". It's a meditation on human attempts to grasp life and existence.
deleted 9y ago
[deleted]
danbruc 9y ago
I have to disagree and I can not really understand what is so appealing about the simulation idea to many. It is an idea that will lead nowhere because you are unable to distinguish a real universe from a simulated one. In order to do this you would have to know what at least one of those scenarios looks like and then compare the universe you observe to what you know to be true about a real or simulated universe. It is common to base such thoughts on analogies between our universe and our computers, i.e. our computers have only finite precision while the universe seems continuous, at least to a very good approximation. Therefore if we would detect rounding errors in the universe we would know that the universe is actually a simulation. But that is at least naive and most likely not true. How would you know that a real universe does not have finite precision? Why would you assume simulation must have finite precision? And you have to answer the same question for any other feature you want to use to make the distinction.
- QAPereo 9y ago
  I have to disagree and I can not really understand what is so appealing about the simulation idea to many. You can’t see the appeal of an unfalsifiable conjecture that everything including us, is an intentional creation of some manner of vast and powerful intelligence? Aliens, Simulators, Bulk Beings, or you know... Gods. It’s just new window dressing on an ancient dream.
  - danbruc 9y ago
    Well, I can neither see the appeal of gods. I guess many people just like to have uncertainty removed from their life even if that is not actually true. And that is probably the point that I don't get, why or how people get something out of those, well let me call them lies.
    - QAPereo 9y ago
      The universe is big and scary, and decidedly not anthropocentric or even comprehensible,.. some people want it to be, decide that it is, and believe that.
  - chr1 9y ago
    The question "whether we live in simulation" is indeed a new dressing. But the question "is simulation possible, and if yes what it can look like" is new, and can have useful answers.
    - QAPereo 9y ago
      But the question "is simulation possible, and if yes what it can look like" is new, and can have useful answers. That is pretty interesting, but now how most people formulate the issue. After all, what we could simulate, or what could be simulated in a universe like ours, in principle is pretty interesting. The question of what another reality simulating us would be like isn't, because it could be absolutely anything at all. Questions without the hope of answers are, to me at least, not interesting.
      - chr1 9y ago
        True, if we go specifically searching for the answer to the second question, we may not find much interesting, but when we know more about the first question we can gain some insights about the second one. So if by not interesting you mean `this door is closed now, revisit later` i completely agree with you!
- indubitable 9y ago
  Personally I find the peculiar implication of a simple question so appealing. Will we eventually be able to create simulations that one would be unable to differentiate from reality if that simulation is all they had ever known? The answer there is quite self evident, yet it simultaneously somehow implies it is highly likely that we are ourselves within a simulation. The reason is that we can safely assume that we are within one of n + 1 realities. The n simulated realities and the 1 real reality. Unless you attribute some sort of exceptionalism bordering on creationism to our existence, there's every reason to think that n is going to proportional to the number of advanced civilizations in existence and is presumably going to be very very large. And as you increase n the odds of us actually being in the 'real' reality, which are of course just 1/(n+1), approach 0. Like you mention it's something that doesn't necessarily go anywhere. Even if you "prove" it after death, that life you'd be experiencing at that point faces the same logical issue - at least unless the argument loses consistency at some point. Something most seem reluctant to admit is that it's also comforting as an atheist. I always expected the infinity of time after my existence to be very much akin to the infinity of time before my existence. That's just disappointing. The seemingly high probability that all is not as it seems is certainly emotionally appealing. But it's certainly not just the emotional appeal driving me there - I could obviously have chosen to invoke Pascal's Wager in the decades of time prior to considering this, but it seemed fake -- this, somehow, does not. It also answers, or at least compellingly kicks the can, of the question of existence. If I write a program to spit out a random number, I presume that there is no entity that suddenly whisks into existence under the false impression that it is choosing a random number - which it then decides upon, before then being whisked out of existence. So why am I, the 'thing' spectating the outcome of the series of chemical and electrical reactions carried out by this body, here? Descartes would have quite the time if the answer to our little question had been yes during his time. It changes the picture so much more than the dreams that drove his ponderances. --- From a scientific point of view, it's obviously not a great concept as it cannot be falsified. And like you mention, it also cannot really be physically proven without begging the question. On the other hand, it can be treated as a soft science and if a preponderance of evidence does lean towards supporting it then we can at least say, "Hmm.. well we can't really say anything for certain, but that's certainly interesting."
  - 9y ago
- elorant 9y ago
  It is appealing for three reasons. 1) As computer engineers we understand it's doable. Give it a couple of centuries and our civilization could reach a computing capacity to simulate the entire observable universe 2) A lot of things just don't make sense. Like consciousness for example. We can't define it, and we don't even know it it's real. If you take consciousness out of the equation humans are just laborious software. 3) This is objective of course, but quite a lot of people are experiencing coincidences that seem unreal. That sounds metaphysics and most of us wouldn't touch it with a barge pole but from a simulation perspective makes total sense. Oh and it makes a lot of people uncomfortable. For me it's one of the best ways to test someone's intellect. You bring it into a conversation and people start feeling unease.
  - andrepd 9y ago
    > Give it a couple of centuries and our civilization could reach a computing capacity to simulate the entire observable universe This is not even remotely true, not even if a perfect Moore's law were to continue for thousands of years. Man, we're hard pressed to even simulate single molecules. > quite a lot of people are experiencing coincidences that seem unreal Oh come on x) "Coincidences" are psychological illusions and misatribution biases at work, not the work of an intelligence behind our universe. This is the "I prayed to god and my back pain healed; it's a miracle" type of thinking.
  - danbruc 9y ago
    As computer engineers we understand it's doable. Give it a couple of centuries and our civilization could reach a computing capacity to simulate the entire observable universe This seems at the very least questionable. Why do you think you can simulate the entire universe just using a tiny fraction of the resources of the universe? It seems to me that could only work if the universe were highly compressible and I don't see any obvious evidence for that. And even then I think it could not work because if the universe is in some sense redundant and could be compressed then it actually provides less resources to work with than if it would not have those redundancies. Take as an analogy for the later two processors executing the same code in lockstep as it is sometimes done for redundancy in safety critical systems. You can mostly get away with only simulating one of the processors but you essentially also only have one processor to work with. And while you can probably simulate the processors on the processors the simulation will probably be at least ten times slower than the actual processor if you only want to use one tenth of the available resources, i.e. clock cycles. And finally memory will be a real problem because you only have as much memory available as you want to simulate.
- gilbetron 9y ago
  Why are you unable to distinguish it? It is not, a priori, impossible. It is entirely possible that there may be ways to determine if we are in a simulation, depending on how the simulation is done. No simulation is perfect, and it is theoretical feasible to find the imperfections.
  - danbruc 9y ago
    To look for imperfections in a simulation requires knowing what the real thing actually looks like. If our universe is a simulation, where do you get the knowledge from what a real universe looks like?
    - chr1 9y ago
      You can look for contradictions, inconsistencies or for macro scale phenomena not explainable by micro scale laws.
      - danbruc 9y ago
        That doesn't work. The rules used by the simulator could just be the rules of the real universe, you can not tell the difference. Or to put in programming terms, you are given an object x to inspect, our universe, and you have to decide whether it is an instance of class RealUniverse or an instance of class SimulatedUniverse but you have no knowledge of what any of those classes looks or behaves like.
        gilbetron 9y ago
        You seem to be arguing that it isn't always possible to detect you are in a simulation, whereas the rest of us are arguing that it could be possible in some simulations.
        jamesrcole 9y ago
        I think they're arguing that whatever evidence you think you've found for it being a simulation could always just be how the universe is.
- breatheoften 9y ago
  Maybe its an acknowledgement of something about the nature of abstraction from observation. Perhaps the true universe is and always be a simulation error away from observation -- under such a hypothesis, science will be an eternal process of finding details in our understanding which are actually accidental results of the simulation capacity of our current understanding, then figuring out how to remove the flaw, and then peaking behind the next curtain ...
- WhitneyLand 9y ago
  You have basically said it may be unprovable. First, that may be true, but it also may not be true. Secondly even if it were true, why would that change anyone’s interest or curiosity about it being a possibility?
  - danbruc 9y ago
    It's nothing special about the simulation idea, there are many similar things. Solipsism, only your mind is real and the outside world may or does not exist. Last Thursdayism, the universe came into existence last Thursday in the exact state of last Thursday, before that there was nothing or something very different. They all share roughly the same idea, there is some reality but by some perfect arrangement of smoke and mirrors you are by definition unable to ever learn something about that reality. There is certainly some value in discussing those ideas on a meta level, finding common characteristics, figuring out limits, but beyond this the individual ideas are, at least in my opinion, mostly a waste of time. What is the point of analyzing something that by definition leaves you stuck? And as far as I can tell philosophy has long ago mostly accepted this and made it something like an axiom that there is an reality and we can learn about it and doesn't concern itself much anymore with ideas that would, if true, block any possible progress.
- dboreham 9y ago
  I'm not sure if the idea appeals to me or not: I was more saying "I've heard Elon and co talking about this and just assumed it was like they'd seen The Matrix again on Netflix...". But reading this article (late, I guess..) the penny dropped when I saw ideas like the boundary conditions are the maximum information density of particles, and the upper bound to information celerity. Starts to sound like the kind of limitations you'd have if you built a huuuugge simulator.
goalieca 9y ago
The article states that axioms they are using for the reconstruction theory end up being abstracted above the underlying reality. It does not suggest the underlying reality is many-worlds, simulation, etc.
charlesism 9y ago
I don't understand what the difference between a "real" and a "simulated" universe would be. It's probably just a word game to make a distinction.

bigtimber 9y ago

Fyi, the topic was discussed a few months back in https://news.ycombinator.com/item?id=15163528 https://news.ycombinator.com/item?id=15163528 after the _Quantamagazine_ article was reprinted in _Wired_.

amelius 9y ago

Any role for Pilot Wave Theory here? https://www.quantamagazine.org/pilot-wave-theory-gains-experimental-support-20160516/ https://www.quantamagazine.org/pilot-wave-theory-gains-exper... > An experiment claims to have invalidated a decades-old criticism against pilot-wave theory, an alternative formulation of quantum mechanics that avoids the most baffling features of the subatomic universe.

wruza 9y ago

After familiarizing with QM/SR concepts some years ago, I came to the conclusion that there is nothing more strange and pointless than the world without these two. If max speed was infinite (or finite but non-relative, which is essentially the same) and there was no probabilistic outcomes, then the world would "happen to the end" instantly and/or with analytically predefined series of events. From any initial state. The entire "consequence" concept would fall apart. There is no point for the universe to exist in classical & atomic-ball electron mode. Idk why both seem so unnatural to so many people who try to get what it means; it feels like it should be obvious instead - it means evolving existence, the only thing you're able to appear in and think about it. Classical uniform fundamental time is much stranger to me than what emerges from what we have now; we simply shifted our focus to "oh" forgetting how much "wtf" was left behind. I'm not claiming any deep-enough physics or math knowledge (layman actually), consider it a funny philosophical view.

chr1 9y ago
> with analytically predefined series of events. This doesn't make universe less interesting or more predictable. Consider Mandelbrots set, it is fully analytically predefined, but only way to find it's details is to perform the whole calculation. Similarly the universe can be predefined, but the only way of finding its state after some amount of time can be performing a calculation fully equivalent to letting the universe to live for that time.
- wruza 9y ago
  >amount of time can be performing a calculation fully equivalent to letting the universe to live for that time This one is very interesting since it brings back the question what time really is. Your point involves “metacircular” observer that can only work/simulate as fast as it can, but the definition of “fast” is external to it. Sure, if we simulate predefined-but-calc-required in our universe, then it will take time. But why should we measure it this way? I mean, does calculation process exist at all without something that requires time for it? [Or we’re really talking about the same fundamental thing that lies behind both our and hypothetically deterministic universe.]

platz 9y ago

> Wins Neutrinos aren't massless Confirmed higgs > Problems Hierarchy problem Fine tuning Why is the cosmological constant so "wrong compared to theory" No evidence for supersymmetry yet at 10^-17cm via LHC No evidence for WIMPs How do we combine QM + GR? Do black holes destroy information? How to solve the BH firewall problem? > Speculation Is there supersymmetry at higher energies than the LHC can probe? Is spacetime doomed? I.e. is space-time a hologram on the boundary or some other emergent phenomenon Is there a multiverse? Is decoherence a solution, or does the wave function "collapse", or simply many-worlds? Is perturbation theory sensible or is there a deeper more elegant way to calculate scattering? Is time emergent or fundamental?