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Roger Penrose claims our Universe has been through multiple Big Bangs

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Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#221

Post by yadingus »

bawolff wrote: post #69
mr_mitm wrote: post #11

Earlier quoted context omitted.

Do you think satisfaction is a good measure of what we should believe to be true?

As an atheist, what other measure should we use? Like when it comes down to it we are all looking for answers that "satisfy" us. What else is there? Logic is just a complex way of verifying that the answers are convincing enough and thus satisfying.

Perhaps one can examine and question why the need for satisfaction.

Is it actually necessary to buy into a theory? To belong to an opinion? Is it beneficial?

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#222

Post by yadingus »

GalenErso wrote: post #5

I know HN hates religion, but after being an atheist all my life, and graduating with a STEM degree (the 'S' part) from a top tier institution, I've started in the last year or so to turn to the church (Roman Catholic) and theism, both to find answers to some of life's mysteries, such as the origin of the Universe, and for personal reasons (I plan to start my initiation, starting with a baptism, within the next year…

Out of curiosity, what would you say to a person who shared the same story as you, but instead of Catholicism they turned to Scientology?

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#223

Post by CuriouslyC »

zamalek wrote: post #118
some_other_time wrote: post #106

This reminds me of something I read some time back. It was about hypervelocity stars, stars with escape velocity. These are stars that are moving fast enough to escape the gravitational pull of their galaxy. If they are escaping their galaxy and moving away from the galactic center, they may also be beyond the pull of any retraction. This, in turn, would mean the subsequent post-retraction Big Bang contains less matt…

Spacetime itself is not limited to slower than light speeds, and the big crunch has nothing to do with gravity. Rogue stars wouldn't escape it. The universe is not finitely/countably infinite. From the perspective of everything inside it, it is truly infinite. You can't escape something that goes on forever.

> The universe is not finitely/countably infinite

If you're saying the universe is infinite in any way, I'm going to need some proof.

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#224

Post by likeabbas »

simonh wrote: post #210
likeabbas wrote: post #129

Earlier quoted context omitted.

> Hossenfelder's thoughts about FTL travel in her video from yesterday I didn't watch said video, but we have theories rooted in GR and Quantum Mechanics that would allow for FTL travel already using negative energy/pressure. We know there exists mechanisms to create negative pressure, like the Casimir effect. We know the universe is non-local, as per the Nobel prize awarded last year. And we are beginning to see exp…

Just to nitpick, the Casimir effect only produces negative pressures relative to the vacuum energy. They're not truly negative. Just in case anyone reading that misunderstands. Also 'violates causality' is an awful lot to unpack, and is glossing over so much nuance that I don't think it's really a meaningful thing to say. For example violation of the Bell inequalities does not rule out superdeterminism, and that has…

You left one portion out of the explanation of the Casimir effect

> The Casimir effect shows that quantum field theory allows the energy density in certain regions of space to be negative relative to the ordinary vacuum energy, and it has been shown theoretically that quantum field theory allows states where the energy can be arbitrarily negative at a given point.[57] Many prominent physicists such as Stephen Hawking,[58] Kip Thorne,[59] and others[60][61][62] therefore argue that such effects might make it possible to stabilize a traversable wormhole.

There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light.

My overall point is it’s weird for scientists to shut down the possibility of FTL travel when we have theories that don’t disprove it outright, especially when we don’t really know whether gravity is a bending in spacetime or is governed by the same rules as QFT. The ER=EPR conjecture really intrigues me, and I think following that path may help lead us to a better understanding of what’s possible.

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#225

Post by GoblinSlayer »

jbotz wrote: post #207
GoblinSlayer wrote: post #204

Earlier quoted context omitted.

Because universe is a physical structure, not mathematical, e.g. you can't define things into existence.

Is it? Says who? This is an untirely unfalsifiable assumption. I personally don't share it. "It from bit"[0], I say, mathematics is fundamental, physical reality is just our perception of the underlying math. [0] Title of a paper by John Wheeler. Can't find it right now, but if you google "it from bit" you'll find a lot of commentary on it.

The concept of fundamentality doesn't exist in mathematics, and it's by design. What is fundamental, Tailor series or Fourier transform? Mathematics doesn't care, it simply has no such concept.

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#226

Post by CuriouslyC »

jstanley wrote: post #156
sidcool wrote: post #154

The concept of infinity seems impossible to me in physical world. It's a great mathematical concept to model our understanding. Just like imaginary numbers. I cannot imagine anything being infinite in the physical world. I find the simulation hypothesis more probable than Universe being infinite. Space and Time is not infinite. It may be Gazillions of centuries old, but not infinity. It can't be.

If you're happy for mathematical structures to be infinite, why can't our universe (including ourselves) just be one infinite mathematical structure? Yes, it's very complex, but there's plenty of room in infinity. It doesn't need to have a "real" physical instantiation anywhere. It's like the simulation hypothesis, except you don't need the simulation. We're just the inside of an infinite self-experiencing mathematic…

Physical systems have finite information storage capacity. Our infinities are descriptions of recursive processes (either iteration or subdivision). The quantization we've observed in the universe is a strike against infinities of subdivision, and it's literally impossible to observe a macro-infinity, so from a scientific perspective physical infinity is unsupported and seems unlikely.

Space might appear "infinite" if you set up a word problem where you fire two photons off in opposite directions and track the distance between them over time, but without an observer the only place information exists is in those photons, and space is meaningless. Infinities of time are likewise artificial constructs of measurement, there is only the current moment.

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#227

Post by mr_mitm »

likeabbas wrote: post #224
simonh wrote: post #210

Earlier quoted context omitted.

Just to nitpick, the Casimir effect only produces negative pressures relative to the vacuum energy. They're not truly negative. Just in case anyone reading that misunderstands. Also 'violates causality' is an awful lot to unpack, and is glossing over so much nuance that I don't think it's really a meaningful thing to say. For example violation of the Bell inequalities does not rule out superdeterminism, and that has…

You left one portion out of the explanation of the Casimir effect > The Casimir effect shows that quantum field theory allows the energy density in certain regions of space to be negative relative to the ordinary vacuum energy, and it has been shown theoretically that quantum field theory allows states where the energy can be arbitrarily negative at a given point.[57] Many prominent physicists such as Stephen Hawking…

> There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light.

But you can't use expansion of space to move matter or to travel. You could even argue that distant galaxies aren't even moving at all, they just appear to do so because the distance between them and us increases. Comparing velocities of distant objects in curved spacetime is tricky in general.

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#228

Post by sangnoir »

slowmovintarget wrote: post #111
elashri wrote: post #87

Earlier quoted context omitted.

But Penrose's field of expertise is Cosmology. So I don't think I get the analogy? I understand that this is a speculation because it is very hard to collect evidence for that claim but it is still within the wide umbrella of what Penrose devoted his career.

That's the point. Penrose's ideas are worth taking seriously because they are directly in line with his field of expertise, and there are means supplied in his papers to rule the ideas out (predictions that should hold true on data we are able to measure). This was a contrast, not an analogy.

What data do we have from the time before the big bang?

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#229

Post by LegitShady »

mr_mitm wrote: post #197
LegitShady wrote: post #189

Earlier quoted context omitted.

I had a hard time understanding the leap she made near the end of her video yesterday about co moving frames. She summarized the time travel theory/paradox as it has been known until now, and then she made some kind of reference to an co moving inertial frame observer ("moving at the same rate as the average of all of the stuff in the universe" paraphrased) she claimed would exist under general relativity. My underst…

No, I have a PhD in physics and you are completely right. I had the same issue with her leap. She implies the co-moving frame is a privileged frame in SR, which is basically equivalent to saying: "SR is wrong and thus FTL travel is possible without time travel". Needless to say this is an extraordinary claim that she glosses over in two sentences of a short Youtube video. She's obviously a very smart and professional…

Maybe she'll post some kind of clarification video. I'm willing to give her the benefit of the doubt that she has an interesting idea that is not well communicated, rather than a bad idea. But until then I basically have no idea how she was trying to suggest that its possible that FTL could exist. I don't really get her logic.

Re: Roger Penrose claims our Universe has been through multiple Big Bangs

#230

Post by likeabbas »

mr_mitm wrote: post #227
likeabbas wrote: post #224

Earlier quoted context omitted.

You left one portion out of the explanation of the Casimir effect > The Casimir effect shows that quantum field theory allows the energy density in certain regions of space to be negative relative to the ordinary vacuum energy, and it has been shown theoretically that quantum field theory allows states where the energy can be arbitrarily negative at a given point.[57] Many prominent physicists such as Stephen Hawking…

> There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light. But you can't use expansion of space to move matter or to travel. You could even argue that distant galaxies aren't even moving at all, they just appear to do so because the distance between them and us increases. Comparing velocities of distant objects in curved spacetime is tricky in general.

The Alcubierre drive gets around this by bending the spacetime around a craft so that portion of space is moving and not the craft through space. And beyond that, traversable wormholes aren’t completely ruled out yet
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