Physicists Debate Hawking’s Idea That the Universe Had No Beginning • Hacker News Board

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#181

Post by pbhjpbhj » Thu, Jun 06, 2019, 9:26 PM UTC

will_brown wrote: post #174

pbhjpbhj wrote: post #166

Earlier quoted context omitted.

On being given the planetary model of an atom I think it's relatively common to consider that maybe atoms are mini star systems. That was one of my early "aw shucks, someone else had that idea already!?" deflationary moments.

That was exactly the early thought and why the commonly accepted image of an atom with a nucleous and orbiting electrons looks just like a solar system. Of course that’s not at all what atoms look like or how they behave.

Do you have a source for that?

AIUI Rutherford's model focussed the mass in the nucleus based-on/inspired-by Nagaoka's Saturnian model. Then Bohr's model specifically put electrons in orbit but they were there to explain atomic emission spectra and so needed to move between orbits - not at all like planets.

I think the thought was that electrons orbited a nucleus in a "planetary" way, rather than them being actual nano-scale planets.

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#182

Post by octachron » Thu, Jun 06, 2019, 9:26 PM UTC

CuriousSkeptic wrote: post #122

Balgair wrote: post #54

Earlier quoted context omitted.

Wikipedia's 'Timeline of the Far Future' is a great article on the posibilities of our universe's fate [0]. Of note are the entries near the end of the list. Year 10^(10^(50)) : Estimated time for a Boltzmann brain to appear in the vacuum via a spontaneous entropy decrease [1] Year 10^(10^(120)) : High estimate for the time for the universe to reach its final energy state, even in the presence of a false vacuum. Year…

If the universe reaches a final state at one point, isn’t the implication that this is where all process that defines time ends. If so, how can one speak of things happening “after” that point?

The final state is a kind of thermal death where thermodynamics say that nothing happens anymore. However, thermodynamics is only an effective theory. It is false on tremendously large time scale: after a very very very large time a random fluctuation can bring down the universe entropy to pre-death level and restart a new non-boring universe (for a very short duration compared to the time spent in the thermal death).

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#183

Post by 6gvONxR4sf7o » Thu, Jun 06, 2019, 9:29 PM UTC

pdonis wrote: post #167

mabbo wrote: post #150

Earlier quoted context omitted.

The problem in your argument is the word 'become'. To 'become', something has to not be so and then later be so- with 'later' implying time on both sides. Hawking's argument is that there is no time on the other side. My interpretation is that the energy of the universe exists in time and space, evolving across the dimension of time. But it has an edge called 'the beginning'. That's the shape of the beast- a defined…

> My interpretation is that the energy of the universe exists in time and space, evolving across the dimension of time. But it has an edge called 'the beginning'. Actually, Hawking's proposal was that there is no "edge". In his proposal, the 4-D spacetime of the universe has no boundary, just as the 2-D surface of the Earth has no boundary. What we call the "beginning" of the universe is more like the South Pole of t…

Is the hypothesis still that the limit as time goes to zero still exists as a part of our universe? In your analogy, is the south pole still a point contained on earth or is it just a point you can get arbitrarily close to?

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#184

Post by golover721 » Thu, Jun 06, 2019, 9:31 PM UTC

For me the hardest idea to grasp is the concept of “nothing”. It seems to me that is something the human brain cannot possibly comprehend. There is always something as far as our senses are concerned. I guess that’s why the idea of nothingness after we die so such a hard notion to comprehend.

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#185

Post by semi-extrinsic » Thu, Jun 06, 2019, 9:35 PM UTC

raattgift wrote: post #129

semi-extrinsic wrote: post #92

Earlier quoted context omitted.

> You can't get to an edge or boundary of space-time because it's not 3-D, it's curved in this really weird way. Can you elaborate? I was under the impression that the curvature is essentially zero and that the universe is open.

We use a Robertson-Walker (RW) metric to describe the universe at the largest scales because it does the job well. There are several components to the (vacuum) RW metric, and two are relevant to your question. Let's take a planar ("equatorial") slice of the expanding universe at a given time. In that slice let's put two test objects that aren't interacting with each other in any way: the gravitational attraction is e…

Mange takk :)

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#186

Post by pdonis » Thu, Jun 06, 2019, 9:36 PM UTC

6gvONxR4sf7o wrote: post #183

pdonis wrote: post #167

Earlier quoted context omitted.

> My interpretation is that the energy of the universe exists in time and space, evolving across the dimension of time. But it has an edge called 'the beginning'. Actually, Hawking's proposal was that there is no "edge". In his proposal, the 4-D spacetime of the universe has no boundary, just as the 2-D surface of the Earth has no boundary. What we call the "beginning" of the universe is more like the South Pole of t…

Is the hypothesis still that the limit as time goes to zero still exists as a part of our universe? In your analogy, is the south pole still a point contained on earth or is it just a point you can get arbitrarily close to?

> the limit as time goes to zero

There is no "time" at the "South Pole" point of the universe, or sufficiently close to it. The spacetime geometry in Hawking's model is purely spacelike in that region, not split up into "space" and "time" parts the way it is now. (As I understand the model, the boundary of the "spacelike" region" is at the beginning of inflation.)

> is the south pole still a point contained on earth or is it just a point you can get arbitrarily close to?

It's still contained.

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#187

Post by heroHACK17 » Thu, Jun 06, 2019, 9:37 PM UTC

golover721 wrote: post #184

For me the hardest idea to grasp is the concept of “nothing”. It seems to me that is something the human brain cannot possibly comprehend. There is always something as far as our senses are concerned. I guess that’s why the idea of nothingness after we die so such a hard notion to comprehend.

Conversely, even the concept of "everything" is hard to grasp. "Everything" in the sense of an infinite universe where everything is realized infinite times over. It's absolutely bonkers to me.

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#188

Post by AgentME » Thu, Jun 06, 2019, 9:38 PM UTC

dmbaggett wrote: post #108

d0m wrote: post #98

Say we could break any physical rules of our current universe, is there a good theory that would explain how something might have been created out of nothing? i.e. imagine for a second that we're in a simulation and that the current laws of physic are just arbitrary created by a "host". This "host" could have very different physical laws. Could we think of any theory that would explain the creation of something out o…

You might be interested in Our Mathematical Universe by Max Tegmark. He tries to argue that, fundamentally, the universe is "just math." In other words (glossing over enormous complexity here) if the basic axioms of math are true, the universe must exist. I have to admit I didn't fully buy the line of reasoning. But it's very interesting.

UD+ASSA (http://fennetic.net/irc/finney.org/~hal/udassa/) is an extension/refinement of the mathematical universe idea that I find very compelling. It explains why even though "everything mathematically describe-able is real", we personally see and anticipate that some things are more likely than other things, including why physics stays the same instead of spontaneously changing, etc. (One of the original authors of the idea thinks there's issues with it, but I think it's still a very useful idea: https://www.lesswrong.com/posts/zd2DrbHApWypJD2Rz/udt2-and-a...)

Since considering it and the mathematical universe idea, the question of why anything exists at all no longer feels so mysterious. Even if there were somehow an objective universe with nothing in it, as long as the basic concepts of logic still held (which of course they do, they don't depend on the universe), then there would still be logical/mathematical structures that describe entities that see themselves as conscious.

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#189

Post by pdonis » Thu, Jun 06, 2019, 9:38 PM UTC

6gvONxR4sf7o wrote: post #183

pdonis wrote: post #167

Earlier quoted context omitted.

> My interpretation is that the energy of the universe exists in time and space, evolving across the dimension of time. But it has an edge called 'the beginning'. Actually, Hawking's proposal was that there is no "edge". In his proposal, the 4-D spacetime of the universe has no boundary, just as the 2-D surface of the Earth has no boundary. What we call the "beginning" of the universe is more like the South Pole of t…

Is the hypothesis still that the limit as time goes to zero still exists as a part of our universe? In your analogy, is the south pole still a point contained on earth or is it just a point you can get arbitrarily close to?

> Is the hypothesis still that the limit as time goes to zero still exists

Note that in other models of the universe, the ones that have an "initial singularity" which can be thought of as "the limit as time goes to zero", the initial singularity itself is not part of the universe; it can be approached as a limit but never reached. (The reason is that spacetime curvature increases without bound as the singularity is approached, and the equations of GR break down at the singularity.)

One of the nice things about Hawking's model is that it totally avoids this problem; spacetime curvature is finite everywhere and there are no singularities and no points where the equations break down.

Re: Physicists Debate Hawking’s Idea That the Universe Had No Beginning

#190

Post by sova » Thu, Jun 06, 2019, 9:40 PM UTC

golover721 wrote: post #184

For me the hardest idea to grasp is the concept of “nothing”. It seems to me that is something the human brain cannot possibly comprehend. There is always something as far as our senses are concerned. I guess that’s why the idea of nothingness after we die so such a hard notion to comprehend.

You have no proof that it's simply nothingness when you die. If this universe has countless beginning points, what makes you consider a single ending point would exist anywhere?