Hawkins

[Meow Mix]

What is your physics specialization? Foundational cosmology? I didn't pursue my PhD after my masters because I couldn't decide on a specialization. I thought particle physics would be for me, but general relativity was infinitely more interesting. I've always liked seeing the connections between ideas and the overall picture...even biophysics has its topics of interest. Anyway, perhaps you've had more cosmology/general relativity than me and can clarify, what do physicists mean when we talk about the age and size of the universe? Is that a quantity that all observers will agree upon regardless of their reference frame? If so, wouldn't that age and size serve as an absolute clock or an absolute measuring rod? To me its no suprise that the assumptions leading to the Robertson-Walker metric would lead to an origin or a "special point" of the universe in time...we assume spacial homology and spacial isotropy but assume a unique "forward" direction in time. Its like assuming a unique "up" direction on the surface of the earth and then being suprised that we have a spacial center in 3-D space. Personally, I think the big bang theory has a major overhaul in store during this century anyway...so I'm not too worried about the beginning of the universe being in conflict with its ontological necessity.

You know, I've never really thought about that. No, observers wouldn't agree on the size of the universe in different reference frames -- though by "size of the universe" we can only talk about the visible universe. An accelerated observer will actually end up with a cosmological horizon behind them as light fails to be able to catch up to them, and in fact they'd experience an increase in heat from "hot" photons. I can't remember the name of the effect, I think it's Unruh or something. (Edit: yes, it's Unruh: http://en.wikipedia.org/wiki/Unruh_effect)

Essentially the cosmological horizon behind them means from their reference frame they lose some of the information about photons in their vicinity, making their motion appear to be random and therefore their thermometers would go up whereas a relatively stationary observer wouldn't observe the same -- and be able to see more of the universe than the accelerated observer.

If we try to ask whether the entirety of the universe is the same size in all reference frames I'd really have to think about that. I'm already aware of one problem with these types of questions: for instance, the Planck distance. Either the Planck distance is absolute or it's not; QM says it is, relativity says it depends on your reference frame. Seems to me like the reverse of the paradox from the ultimate small to the ultimate large.

As for the "forward arrow" in time it's a consequence of deep thermodynamics... which are themselves a consequence of sheer probabilities. The RW metric is mostly just based on homology and isotropy; the only factor/assumption that bothers with an arrow of time is the scale factor a(t) which is based on relative expansion as far as I know. We preeeeetty much just sort of plug in what we gather to be the "start" of the universe based on our other methods for calculating the age of the universe, so really the metric doesn't make a statement on there being a special "time" -- we arbitrarily choose those times and plug them in. In this case we just sorta say that the BB event is the "start" even if it doesn't mean it's the start of de facto existence altogether.

 

[logician]

I thought in current multiverse theories that our universe could be one of a great number or even an uncountable number of universes, either dying, or in the process of being born. The presumption is that "something", i.e. matter and energy have always existed, which means that a creator "god" (whatever that is), is not needed.

 

[Meow Mix]

I thought in current multiverse theories that our universe could be one of a great number or even an uncountable number of universes, either dying, or in the process of being born. The presumption is that "something", i.e. matter and energy have always existed, which means that a creator "god" (whatever that is), is not needed.

Multiverse conjecture is currently unsupported by any empirical evidence and thus remains in the realm of metaphysics rather than science.

 

[Autodidact]

*is experiencing brain envy of Meow Mix*

 

[Reptillian]

You know, I've never really thought about that. No, observers wouldn't agree on the size of the universe in different reference frames -- though by "size of the universe" we can only talk about the visible universe. An accelerated observer will actually end up with a cosmological horizon behind them as light fails to be able to catch up to them, and in fact they'd experience an increase in heat from "hot" photons. I can't remember the name of the effect, I think it's Unruh or something. (Edit: yes, it's Unruh: Unruh effect - Wikipedia, the free encyclopedia)

Essentially the cosmological horizon behind them means from their reference frame they lose some of the information about photons in their vicinity, making their motion appear to be random and therefore their thermometers would go up whereas a relatively stationary observer wouldn't observe the same -- and be able to see more of the universe than the accelerated observer.

I'm imagining a world where this isn't true. I'm picturing a bunch of guys flipping coins by the side of the road while I drive by in my car. I step on the gas and suddenly all their coins come up heads.

If we try to ask whether the entirety of the universe is the same size in all reference frames I'd really have to think about that. I'm already aware of one problem with these types of questions: for instance, the Planck distance. Either the Planck distance is absolute or it's not; QM says it is, relativity says it depends on your reference frame. Seems to me like the reverse of the paradox from the ultimate small to the ultimate large.

This Planck length paradox reminds me of a question an old professor of mine once asked me. He asked, "If I built a machine that could slow time down everywhere throughout the universe and clicked the on switch, how would I be able to tell if it worked?" I never did come up with a good answer for him, I told him I thought it might mess with the speed of causality bust wasn't sure.

As for the "forward arrow" in time it's a consequence of deep thermodynamics... which are themselves a consequence of sheer probabilities. The RW metric is mostly just based on homology and isotropy; the only factor/assumption that bothers with an arrow of time is the scale factor a(t) which is based on relative expansion as far as I know. We preeeeetty much just sort of plug in what we gather to be the "start" of the universe based on our other methods for calculating the age of the universe, so really the metric doesn't make a statement on there being a special "time" -- we arbitrarily choose those times and plug them in. In this case we just sorta say that the BB event is the "start" even if it doesn't mean it's the start of de facto existence altogether.

The assumption of homology and isotropy in the RW metric is that of spacial homology and isotropy, not spacetime. My understanding was that we assume a distinct past and a distinct future in the time direction...so that when I take 3-D space "slices" of 4-D spacetime those are what satisfy our assumptions. right?

 

[Meow Mix]

I'm imagining a world where this isn't true. I'm picturing a bunch of guys flipping coins by the side of the road while I drive by in my car. I step on the gas and suddenly all their coins come up heads.

I'm not quite following. If you step on the gas and you end up with a cosmological horizon behind you then you won't see the coins at all.

Now, if the guys flipping coins were flipping... say, pairs of coins, slingshotting them in either direction in quantum entanglement so that if one coin in a pair comes up heads the other necessarily comes up tails there might be an analogy to be made there...

This Planck length paradox reminds me of a question an old professor of mine once asked me. He asked, "If I built a machine that could slow time down everywhere throughout the universe and clicked the on switch, how would I be able to tell if it worked?" I never did come up with a good answer for him, I told him I thought it might mess with the speed of causality bust wasn't sure.

Haha. That's a good one, however it seems to me that spacetime is relational so there would be no difference... spacetime is to me like a sentence, it only makes sense in that it's an order and syntax of words. Doesn't much make sense to say a sentence makes sense with only one word or without any words; same with time if it's treated as a single entity (whole universe).

The assumption of homology and isotropy in the RW metric is that of spacial homology and isotropy, not spacetime. My understanding was that we assume a distinct past and a distinct future in the time direction...so that when I take 3-D space "slices" of 4-D spacetime those are what satisfy our assumptions. right?

Oh, right -- yes, there's still an assumption of a distinct past and future, hence the need to pick a "starting point" with the a(t) scalar.

All in all I'm just a first year grad student, I prooobably don't know that much more than you beyond that.

 

[Kathryn]

Not ironic at all, just business as usual. You shouldn't expect Christians to actually live the words they mouth. At the end of the day they can simply ask to be forgiven their intemperate bashing and insulting behavior and it's given.

I haven't read the article (and am disinclined to do so) nor have I read any rebuttals to it by Christians. So I am speaking generally.

The OP asked if it was hypocritical for Christians to call someone out and criticize them, to express themselves harshly - apparently the poster (and some others) think that Christians are bound by the teachings of their faith to walk about with their hands folded in prayer, smiling benignly and gently murmuring "God bless us every one."

Christians should follow the example set by Jesus. Even Jesus could be pushed too far - and if you read the Gospels, you may be surprised at the Jesus who emerges from those accounts. Jesus was kind, tender hearted, gentle, and loving. He also was very infuriating in his interactions with the Roman and Jewish leadership during his trial, and scathing in his sarcasm and cutting wit when addressing the hypocritical scribes and Pharisees. He also went on a rampage when he saw the temple being used as a marketplace - overthrowing tables and yelling at the vendors to "Get out of his Father's house."

So even Christians are allowed to feel, and express, anger and even ridicule in some cases.

Not all anger, and not all sarcasm, is misplaced or inappropriate - not even when coming from a Christian.

I hope I've made myself clear, you JACKWAGONS!

 

[JustWondering]

He also went on a rampage when he saw the temple being used as a marketplace - overthrowing tables and yelling at the vendors to "Get out of his Father's house."

So throwing violent temper tantrums is an endorsed Christian practice?

 

[Smoke]

I'm just a first year grad student

And yet I don't understand what you're talking about. That makes me feel like I've wasted my entire life up to now. I've got to find a way to educate myself better.

 

[Tiapan]

But then again, I'm a bit drunk and rambling...nice day outside...brub brub bub bub bub....

Had a very trying week so TGIF, result a little whiskey influenced also.

I agree with Hawking I think. If God exists, he must exist as a logical necessity, but we are uncertain that God exists. We know the universe exists, so it might as well exist as a logical necessity. If its possible to prove logically that God must exist, then we might as well replace the word God with the word universe and cut out the middle man. Hell, we may as well replace the word universe with logic and conclude that reason is all that exists.

Whilst I agree with his premise I think we can explore further in that the god that is equivalent to our current universe, is remarkable yet unaccepted by most mainstream Abrahamic religions. Where the god if equivalent to our current universe is impersonal and most often predictable, unlike the gods of the abrahamic religions, where the ? (universe) is anthromorphologized into a consumable package of patriarchal social control system. This god is supposed to have a direct involvement with us important humans at the expense of any other lifeforms here or elsewhere.

This all smacks of smart minds manipulating the less intellectually endowed, for purposes beyond the supernatural. There maybe an incorrect assumption by many that that god is unprovable. I believe I can with some credibility show 2 aspects of natural universal physics and mathematics, that minimize the probability of the version of god as portrayed in Abrahamic religions.

One is entropy which in a nutshell says information complexity is inversely proportional to temperature and exponentially proportional to universal complexity. So God may not have "been" yet, but may be in some distant future when complexity is at a universal maximum and a lot colder the possibility of an omnieverything being may be realized, shortly before the universe freezes over in the dark void.

The other is if the universe itself is rotating, the universal law of conservation of angular momentum demands that if there was a big bang (Expansion) its precursor was also rotating. Hence the possible scenario of an oscillating universe with no beginning or end hence no need for a creator as all this stuff (the universe) has always and will always, just exists, Simple really.

Cheers

 

[T-OI]

And yet I don't understand what you're talking about. That makes me feel like I've wasted my entire life up to now. I've got to find a way to educate myself better.

Yeah, i agreed on that one XD i mean..wow, i only know a tiny bit of what you guys are talking about. I need to learn more XD

Oh and one of my professor said, "if you want to know if god existed or not, go suicide and make your way to the afterlife and see the god ( if it existed ) if not you'd died a shameful death."

 

[Kathryn]

So throwing violent temper tantrums is an endorsed Christian practice?

I'll tell ya what - you read the accounts in the gospels of Jesus in the Temple, and get back with me. We can discuss this then.

 

[Reptillian]

I'm not quite following. If you step on the gas and you end up with a cosmological horizon behind you then you won't see the coins at all.

Now, if the guys flipping coins were flipping... say, pairs of coins, slingshotting them in either direction in quantum entanglement so that if one coin in a pair comes up heads the other necessarily comes up tails there might be an analogy to be made there...

I guess I was looking at it this way: the guy accelerating perceives his loss of knowledge about the universe as an increase in entropy...so I imagined a world where the effect wasn't true and you have a decrease in entropy while accelerating. I just illustrated the system by thinking of the entropy of coin flipping.

And yet I don't understand what you're talking about. That makes me feel like I've wasted my entire life up to now. I've got to find a way to educate myself better.

Don't worry about it too much. Whenever I talk about this kind of stuff with my friends and explain it in everyday terms they're always like, "This is what scientists actually think the world is like...thats crazy." If they're right, then we're all deluded and insane...but then again maybe Plato was right and people who have experienced truth appear insane to people who haven't...maybe Pascal was right when he said that "Man is so necessarily mad, that to not be mad would amount to another form of madness." One of my favorite quotes.

Had a very trying week so TGIF, result a little whiskey influenced also.



Whilst I agree with his premise I think we can explore further in that the god that is equivalent to our current universe, is remarkable yet unaccepted by most mainstream Abrahamic religions. Where the god if equivalent to our current universe is impersonal and most often predictable, unlike the gods of the abrahamic religions, where the ? (universe) is anthromorphologized into a consumable package of patriarchal social control system. This god is supposed to have a direct involvement with us important humans at the expense of any other lifeforms here or elsewhere.

This all smacks of smart minds manipulating the less intellectually endowed, for purposes beyond the supernatural. There maybe an incorrect assumption by many that that god is unprovable. I believe I can with some credibility show 2 aspects of natural universal physics and mathematics, that minimize the probability of the version of god as portrayed in Abrahamic religions.

One is entropy which in a nutshell says information complexity is inversely proportional to temperature and exponentially proportional to universal complexity. So God may not have "been" yet, but may be in some distant future when complexity is at a universal maximum and a lot colder the possibility of an omnieverything being may be realized, shortly before the universe freezes over in the dark void.

The other is if the universe itself is rotating, the universal law of conservation of angular momentum demands that if there was a big bang (Expansion) its precursor was also rotating. Hence the possible scenario of an oscillating universe with no beginning or end hence no need for a creator as all this stuff (the universe) has always and will always, just exists, Simple really.

Cheers

Always nice to see a fellow drinker. Back when I was still trying to salvage my Christian faith and reconcile it with what I knew about science, I embraced a kind of panentheism. Eventually my views about the nature of God became so abstract that I realized I wasn't talking about the same thing that everyone else was. I figured that if God only exists as a philosophical abstraction, and doesn't care about people or their lives, then what is the point in worshipping it?

Godel's rotating universe solution to Einstein's equation always makes me squirm in my seat a little bit. Rotating with respect to what is the problem. Like Einstein, I think this shows that there is something wrong with general relativity. It certainly doesn't seem in tune with Mach's ideas about the relative nature of motion. There is also the problem that such a universe allows time travel into the past.

Yeah, i agreed on that one XD i mean..wow, i only know a tiny bit of what you guys are talking about. I need to learn more XD

Oh and one of my professor said, "if you want to know if god existed or not, go suicide and make your way to the afterlife and see the god ( if it existed ) if not you'd died a shameful death."

Shakespeare..."Better to bear those ills we have than fly to others that we know not of."

 

[Reptillian]

I'll tell ya what - you read the accounts in the gospels of Jesus in the Temple, and get back with me. We can discuss this then.

I've always liked that story...rather than put up with sacrilige, ill gotten gains, and hypocracy in the name of religion...Jesus actually got a little ticked off. It shows he wouldn't be too happy with all these modern people who hoard wealth by preying upon people's beliefs. There are a lot of religious hypocrites I'd like to grab by the ears and kick out of the temple too.

 

[logician]

Multiverse conjecture is currently unsupported by any empirical evidence and thus remains in the realm of metaphysics rather than science.

Most cosmological theories like string theory are in that cateogory, the point is, as Hawking said, there is no need for a creator god.

 

[Willamena]

Most cosmological theories like string theory are in that cateogory, the point is, as Hawking said, there is no need for a creator god.

He's right about that - "God" shouldn't be about what we need.

 

[no-body]

I've always liked that story...rather than put up with sacrilige, ill gotten gains, and hypocracy in the name of religion...Jesus actually got a little ticked off. It shows he wouldn't be too happy with all these modern people who hoard wealth by preying upon people's beliefs. There are a lot of religious hypocrites I'd like to grab by the ears and kick out of the temple too.

Yep I like how Christians miss the entire point of the story and try to use it as justification to act like jerks.

Jesus only ever got really ticked at two groups of people, the hypocritical rich and pharisees but that is greatly ignored. Like when he breaks bread with sinners, they always leave out that he never asked any of them to convert or to be forgiven.

 

[logician]

He's right about that - "God" shouldn't be about what we need.

I also don't want one.

 

[Smoke]

So throwing violent temper tantrums is an endorsed Christian practice?

Obviously. How can you live in Arizona without knowing any Christians?

 

[Kathryn]

I've always liked that story...rather than put up with sacrilige, ill gotten gains, and hypocracy in the name of religion...Jesus actually got a little ticked off. It shows he wouldn't be too happy with all these modern people who hoard wealth by preying upon people's beliefs. There are a lot of religious hypocrites I'd like to grab by the ears and kick out of the temple too.

Jesus was angry with the fact that the religious leaders of the day had allowed the Temple to be used as a market place rather than keeping it strictly for religious worship and practices. He wasn't simply railing against "these modern people who hoard wealth by preying upon people's beliefs" though I'm sure some of the participants in the Temple market were guilty of exactly that.

And yes - these mega churches and televangelists and pastors who make $400,000 a year from the tithes of those of their congregation who live off disability or social security - they will have to answer for this sacrilege.