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Roger Penrose Changed His Mind About the Big Bang #science #universe
TL;DR
A leading physicist abandoned the idea that quantum gravity explains the Big Bang’s unusual time asymmetry, arguing instead that the problem lies elsewhere.
KEY POINTS
A Shift Away from Quantum Gravity
A prominent physicist spent years pursuing the idea that quantum gravity could explain the Big Bang’s extreme time asymmetry, believing the theory itself might be fundamentally time-directional. This approach assumed that the early universe’s highly ordered state required an equally unusual underlying framework.
The Puzzle of Time Asymmetry
The Big Bang presents a striking contrast: it appears highly ordered and low-entropy, while the laws of physics are largely time-symmetric. This mismatch has long been a central problem in cosmology, raising questions about why time appears to flow in one direction.
Black Holes vs. the Big Bang
Singularities inside black holes are understood to be chaotic and complex, with wildly varying curvature. By contrast, the Big Bang’s singularity appears unusually smooth and special. This stark difference suggests that not all singularities are alike, challenging attempts to unify them under a single explanation.
Rejected Hypothesis of “Exotic” Quantum Gravity
The earlier theory proposed that quantum gravity might be a peculiar, time-asymmetric system capable of producing the Big Bang’s unique properties. Over time, this idea was abandoned as it failed to convincingly explain why such a dramatic asymmetry would arise.
Tension with Popular Modern Theories
Many current approaches, such as emergent spacetime models, attempt to derive spacetime from deeper quantum structures like qubits. These frameworks often assume quantum mechanics as the foundation, but they do not naturally resolve the Big Bang’s special initial conditions.
Conclusion: Not a Quantum Gravity Problem
The physicist ultimately concluded that the issue is not rooted in quantum gravity at all. The scale and obviousness of the time asymmetry suggest a more fundamental explanation is required, one that does not rely on modifying quantum theory.
CONCLUSION
The failure of quantum gravity to account for the Big Bang’s unique order highlights a deeper unresolved problem about the origin of time asymmetry in the universe.
Full transcript
One of the greatest physicists alive spent years chasing the wrong answer about the big bang. >> What do you think of that attempt? Well, I used to think that. I thought, well, it it's got to be quantum gravity, but since you got to have something extremely asymmetrical in time. So maybe quantum gravity is a very peculiar theory which is asymmetrical in time. And I went through several years of my life thinking that and then I changed my mind. That's not the answer. >> [laughter] >> But I did that was my sort of solution. The quantum gravity had to be a very peculiar time asymmetrical theory and big bang was a quantum gravity which had this funny I say had to be time asymmetrical because the big bang were so very special and all the singularities in black holes and all are very very general. They're completely different. The ones in black holes would be very complicated with this informal curve which you're going to infinity get going completely wild and these Russians worked out what they might be looked looked at look like and so on. No, I accepted all that. Nothing like what the big bang was like. So there's something very peculiar about the big bangs. Not like any old singularity. That's right. Because probably the most fashionable approaches at the moment are to so approaches like so-called emergent spacetime where you essentially picture quantum mechanics as the base framework and you attempt to uh see how spacetime would emerge from some underlying theory. It could be a network of cubits or whatever it is. >> Eventually I lived out of that phase. Did you because that's what most not most maybe but many physicists would would say today certainly with work on black holes and the black hole information paradox and so on. So why did you why did you uh what do you say grow out of it? I think the thing was to realize it was not a quantum gravity problem. That's the thing you see because it doesn't I mean if it were you wouldn't get this huge asymmetry and it's in your in your face. It's not a subtlety it completely in your face. But my sort of solution was to think that quantum gravity is a very strange theory which is time asymmetrical. Well I eventually lived out of that phase my life and thinking no no that's not the answer. So my my answer is something which people still have trouble believing in.