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On 28-Jul-08 23:27, Warp wrote:
> andrel <a_l### [at] hotmail com> wrote:
>> I have apparently missed a lot since my physics study. I was under the
>> impression that the size of the universe is of the order of a sphere
>> with a radius of the age of the universe times the speed of light. Could
>> you give a pointer to those current theories that you mentioned?
>
> Glad you asked.
>
> It is, in fact, a rather common misconception that the theory of
> relativity limits the speed at which the universe can expand
is it?
> (even
> some scientists and cosmology papers hold this misconception).
yup, this physicist for instance.
> However, the theory of relativity does not limit the speed at which
> the universe can expand. The distance between two points in the universe
> can grow faster than c without it breaking relativity.
yup, but that has no additional implication for the speed at which the
universe can expand.
> The reason why
> people get confused is that they tend to think that if the distance
> between two points increases at a rate which is larger than c, that means
> that the points are *moving* away from each other faster than c, thus
> breaking relativity. However, the points are not moving. The space
> geometry between them is changing (in very simplistic terms, new space
> appears between them). This is summarized, for example, here:
>
> http://en.wikipedia.org/wiki/Metric_expansion_of_space
yes, but as I said above that has no implication for the size of the
universe.
>
> "The metric expansion leads naturally to recession speeds which exceed
> the "speed of light" c and to distances which exceed c times the age
> of the universe, which is a frequent source of confusion among
> amateurs and even professional physicists.[1] The speed c has no
> special significance at cosmological scales."
>
> No information of any type whatsoever can be transferred by any means
> between two points which are recessing faster than c. This is exactly
> what causes the so-called cosmological horizon (stub article at
> http://en.wikipedia.org/wiki/Cosmological_horizon )
>
> In fact, assuming that the borders of the universe had always grown
> at a constant rate of c is against observation. Moreover, it has been
> conjectured that the universe suffered an exponential inflation period
> at its first moments, which would explain many observed phenomena. This
> is an interesting article about the subject:
>
> http://en.wikipedia.org/wiki/Cosmic_inflation
And what exactly does this all prove? I haven't seen anything in those
links that I did not know (but I admit I did not read everything) and
nothing that even remotely supports your 'The real size of the universe
is completely impossible to know. It could be just slightly larger than
the observable universe, or it could be staggeringly larger. There's
just no way of knowing.' but I might have missed it.
Unless you are in a roundabout way referring to the problem that you can
not define the 'now' for which you are computing the size.
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On 28-Jul-08 23:33, somebody wrote:
> "Orchid XP v8" <voi### [at] devnull> wrote in message
> news:488e046e$1@news.povray.org...
>> somebody wrote:
>>
>>> Do you really find it easy to visualize the number of subatomic
> particles in
>>> the visible universe? I don't see why thinking about that would be more
>>> informative than, say, 1E80.
>> Well, the number of grains of sand on the entire English coastline is
>> "obviously" a pretty damned big number. And the number of subatomic
>> particles in the universe is equally obviously *very* much larger.
>>
>> Call it a failure of the simplistic human mind, but seeing a handful of
>> symbols on a page isn't very impressive. Likening it to something that
>> at least "feels real" makes it slightly easier to grasp.
>>
>> For example, off the top of your head, how long is "10^14 seconds"?
>
> It's 10^14 seconds.
>
>> I mean, is that like, months? Millenia? What?
>
> 1 year is close to PI*10^7 seconds (something easy to remember), so it's
> close to PI*10^7 years.
<nitpick> that'll be 1/PI*10^7 or (as PI^2 is almost 10) PI*10^6 </nitpick>
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"Kevin Wampler" <wampler+pov### [at] uwashingtonedu> wrote in message
news:488e4494$1@news.povray.org...
> Warp wrote:
>> Hmm, I wonder if you aren't confusing it with the Polya conjecture...
>> (which is famous for having a rather big counter-example).
>
>
> Nope,
Heh, I knew you were going to say "Nope" before I looked at your reply.
:)
Time for bed said Zebedee...
~Steve~
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St. wrote:
> Heh, I knew you were going to say "Nope" before I looked at your reply.
> :)
Clearly I have become far too tomato.
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andrel <a_l### [at] hotmailcom> wrote:
> And what exactly does this all prove? I haven't seen anything in those
> links that I did not know (but I admit I did not read everything) and
> nothing that even remotely supports your 'The real size of the universe
> is completely impossible to know. It could be just slightly larger than
> the observable universe, or it could be staggeringly larger. There's
> just no way of knowing.' but I might have missed it.
Uh? I said that the current widely agreed consensus is that the universe
not only can expand faster than c (which you don't seem to disagree with),
but most probably has done so (because that would explain many observed
phenomena). I gave links to wikipedia pages where you could find references
to more material.
Of course there's no absolute *proof* of this. By the very definition
of cosmological horizon it's *impossible* to have an absolute proof of
this (ie. that the universe is larger than the observable universe).
However, currently science most agrees that this is very likely.
Your way of writing seems to imply something like "you have not given
me any proof about this, and thus I don't believe you". In other words,
you still state that the size of the universe is at most the size of
a sphere with a radius of the age of the universe itmes the speed of
light (although you don't seem to deny that the universe *can* expand
faster than c).
Well, where's your proof? Or any serious references, for that matter.
At least I gave you *something*.
--
- Warp
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Invisible <voi### [at] devnull> wrote:
> Does anybody know of a list anywhere that gives examples of really large
> numbers? I'm thinking of things like the number of grains of sand in a
> cubic meter, the brain cells in a human brain, or the number of
> subatomic particles in the visible universe. I for one have no idea even
> approximately "how big" these numbers are.
I'd recommend Project Euler ( projecteuler.net ). It's a couple hundred math
problems for the not-particularly-mathematically-inclined whose answers are all
moderately large integers, e.g. the sum of the digits in 100!. (That's
factorial, not emphasis.) You create an account and can't see the answer...
until you have the answer. Most require programming, but a good share require
nothing more than brute force. Realizing how quickly problems become
intractable with brute force though will give you a real appreciation for how
quickly numbers grow. Fun too.
- Ricky
P.S. Keep your distance from #160. I lost at least a couple evenings to that
one. Never figured it out.
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Invisible wrote:
> the brain cells in a human brain,
>
Human brain was thought to be about 10^11 neurons.
Hit google books search and look for "On Number Numbness" by Hofstadter,
right up your alley I think.
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> For example, off the top of your head, how long is "10^14 seconds"? I
> mean, is that like, months? Millenia? What?
GIYF
http://www.google.com/search?q=1e14s+in+millenia
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Warp wrote:
> Another interesting (and nerdier) example:
>
> Assume we have a 3GHz processor, and that it can increment a 32-bit
> register at each clock cycle. How long does it take to go through all
> the values of that register?
Ooo... 2^32 = 4 billion. 3 GHz = 3,000,000,000 incriments per second. So
we have... a little over 1 second.
> Now assume that it's a 64-bit register instead. How long does it
> take now?
2^64 = (2^32)^2, so if 2^32 takes 1 second, 2^64 should take 4 billion
seconds (which is about 136 years). So... a ****ing long time then.
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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And lo on Mon, 28 Jul 2008 17:44:55 +0100, Warp <war### [at] tagpovrayorg> did
spake, saying:
> Another funny example, which you can use on someone: Assume you have
> a really, really large piece of cardboard which is 1 mm thick. Also
> assume
> that you can fold it in half as many times as you want (thus doubling its
> thickness each time you fold it). How many times do you have to fold it
> before the thickness reaches the Moon?
31 times to roughly match the length of the UK. 40 times will easily reach
the Moon and about 58 times to get very close to the Sun. Yeah I was bored.
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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