Re: From Atheism to Islam

[Brent Meeker]

On 2/18/2017 3:14 PM, John Clark wrote:
On Sat, Feb 18, 2017 at 5:07 PM, Brent Meeker >wrote:


​> ​
he
​[Einstein] ​
didn't notice that it was an unstable equilibrium - a very
elementary mistake.


​I would humbly submit that when trying to figure out what 
4-dimensional non-Euclidean

Tensor calculus
​is telling you about physics ​
nothing
​ is very elementary, especially not in 1917.​

​> ​
But the holographic principle can yield a value close the the
observed.


​How close? In science ​if your theory predicts something that differs 
from the observed value by a factor of 2 that's generally considered 
to be pretty damn bad, and we're talking about 10^120. They may have 
come up with something closer than 10^ 120, but close? I don't think 
so;at least not unless they worked backward and invented a 120 digit 
number and inserted it ad hoc into the theory so things come out right.


It's not a matter of working backward; it's discarding the idea that 
quantum fields zero-point energy fills volumes of space.   From Hsu's paper;




Note that Lambda_qm is the value that has been calculated as off by a 
factor of 1e120.  Lambda_0 is a purely geometrical term - Einstein's 
constant of integration.  The current estimate is 1e-12 eV^4.  So Hsu is 
off by two orders of magnitude on the negative energy density.


Brent


But that would be cheating because if you can't get more out of a 
theory than you put in it has no use, and a 120 digit number is a lot 
to put in. I don't think we're going to have a good explanation for 
Dark Energy anytime soon, but I hope I'm wrong.


​> ​
Sean Carroll has considered this in his review article
https://arxiv.org/abs/astro-ph/0004075v2



​That article is 17 years old, and Dark Energy is as big a mystery now 
as it was then.


John K Clark​



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Re: From Atheism to Islam

[John Clark]

On Sat, Feb 18, 2017 at 5:07 PM, Brent Meeker  wrote:


> ​> ​
> he
> ​[Einstein] ​
> didn't notice that it was an unstable equilibrium - a very elementary
> mistake.
>

​I would humbly submit that when trying to figure out what 4-dimensional
non-Euclidean
Tensor calculus
​is telling you about physics ​
nothing
​ is very elementary, especially not in 1917.​



> ​> ​
> But the holographic principle can yield a value close the the observed.
>

​How close? In science ​if your theory predicts something that differs from
the observed value by a factor of 2 that's generally considered to be
pretty damn bad, and we're talking about 10^120. They may have come up with
something closer than 10^ 120, but close? I don't think so; at least not
unless they worked backward and invented a 120 digit number and inserted it
ad hoc into the theory so things come out right. But that would be cheating
because if you can't get more out of a theory than you put in it has no
use, and a 120 digit number is a lot to put in. I don't think we're going
to have a good explanation for Dark Energy anytime soon, but I hope I'm
wrong.


> ​> ​
> Sean Carroll has considered this in his review article
> https://arxiv.org/abs/astro-ph/0004075v2
>

​That article is 17 years old, and Dark Energy is as big a mystery now as
it was then.

John K Clark​



>

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Re: From Atheism to Islam

[Brent Meeker]

On 2/18/2017 10:18 AM, John Clark wrote:
On Fri, Feb 17, 2017 at 11:19 PM, Brent Meeker > wrote


​> ​
The cosmological constant appears as an integration constant in
solutions to Einstein's equations.
​


​Yes, so mathematically it could have any value including zero. ​

​> ​
It would be good to know more about the CC, but we actually "know"
more about it than we do about dark matter.

The Cosmological Constant​​ amount
​s​
​​ to a repulsive effect that comes​ ​from space itself, and
​ ​
you can set that constant to anything and mathematically the field​ 
​equations of General Relativity would still work​ just fine​. 
Originally Einstein​ ​saw no physical reason for that additional 
complication so he set it to​ ​zero. But then he noticed that if it 
was zero the universe could not be​ ​stable,


No, he saw that it could not be in equilibrium.  He put in the CC and 
gave it a value that balanced the gravitational attraction of the 
observed matter so that the system was in equilibrium.  However, he 
didn't notice that it was an unstable equilibrium - a very elementary 
mistake.



it must be expanding or contracting
​ ​
and​ at the time everybody​ ​including Einstein thought the universe 
was stable so he set it to a non​ ​zero value and the cosmological 
constant was born. However just a few​ ​years later Hubble found the 
universe was expanding, so Einstein​ ​thought the cosmological 
constant no longer had a purpose and said that​ ​changing it from zero 
was the greatest mistake of his life.​

​​


Right.  Einstein was a genius who was so smart that when the thought he 
made a mistake, he was wrong.





​Then​ people working with quantum mechanics found that empty space​ 
​should indeed have a repulsive effect, but the numbers were huge,​ 
​gigantic astronomical, so large that the universe would blow itself

​ ​
apart in
​much​
less than a billionth of a​ trillionth of a​ nanosecond. This was 
clearly a nonsensical result but most felt that once a quantum theory 
of gravity was discovered a way would be found to cancel this out and 
the true value of the cosmological constant would be zero.


​But then​
 just a few years ago it was observed that the universe is not just 
expanding but accelerating, so now theoreticians must find a way to 
cancel out, not the entire cosmological constant, but the vastly more 
difficult task of canceling it all out *EXCEPT* for one part in 
10^120. There are only about 10^90 atoms in the observable universe.

​ Nobody has a clue how to do this.​


Actually there are several ideas about how to do this - but none that 
have been worked out to the point of being testable.  One is my friend 
Vic Stenger's idea that one should take the Bekenstein bound on entropy 
seriously and apply it to the Hubble volume.  The 10^120 number comes 
from assuming that each quantum field contributes zero-point energy down 
to de Broglie wavelengths as small as the Planck length, L. But the 
holographic principle can yield a value close the the observed.


http://journals.aps.org.secure.sci-hub.ac/prl/pdf/10.1103/PhysRevLett.89.081301

This is not generally accepted at "the solution" because it seems to 
imply the wrong equation of state for inflation; but there may be ways 
around this:


https://arxiv.org/pdf/hep-th/0403052.pdf

Sean Carroll has considered this in his review article 
https://arxiv.org/abs/astro-ph/0004075v2


/More generally, it is now understood that (at least in some 
circumstances) string theory//
//obeys the “holographic principle”, the idea that a theory with gravity 
in D dimensions//
//is equivalent to a theory without gravity in D−1 dimensions [148, 
149]. In a holographic//
//theory, the number of degrees of freedom in a region grows as the area 
of its boundary,//
//rather than as its volume. Therefore, the conventional computation of 
the cosmological//
//constant due to vacuum fluctuations conceivably involves a vast 
overcounting of degrees//
//of freedom. We might imagine that a more correct counting would yield 
a much smaller//
//estimate of the vacuum energy [150, 151, 152, 153], although no 
reliable calculation//

//has been done as yet

/Brent/
/



 John K Clark




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Re: From Atheism to Islam

[John Clark]

On Fri, Feb 17, 2017 at 11:19 PM, Brent Meeker  wrote


> ​> ​
> The cosmological constant appears as an integration constant in solutions
> to Einstein's equations.
> ​
>

​Yes, so mathematically it could have any value including zero. ​


> ​> ​
> It would be good to know more about the CC, but we actually "know" more
> about it than we do about dark matter.
>

The Cosmological Constant​​ amount
​s​
​​ to a repulsive effect that comes​ ​from space itself, and
​ ​
you can set that constant to anything and mathematically the field​
​equations of General Relativity would still work​ just fine​. Originally
Einstein​ ​saw no physical reason for that additional complication so he
set it to​ ​zero. But then he noticed that if it was zero the universe
could not be​ ​stable, it must be expanding or contracting
​ ​
and​ at the time everybody​ ​including Einstein thought the universe was
stable so he set it to a non​ ​zero value and the cosmological constant was
born. However just a few​ ​years later Hubble found the universe was
expanding, so Einstein​ ​thought the cosmological constant no longer had a
purpose and said that​ ​changing it from zero was the greatest mistake of
his life.​
​​


​Then​ people working with quantum mechanics found that empty space​
​should indeed have a repulsive effect, but the numbers were huge,​
​gigantic astronomical, so large that the universe would blow itself
​ ​
apart in
​much​
less than a billionth of a​ trillionth of a​ nanosecond. This was clearly a
nonsensical result but most felt that once a quantum theory of gravity was
discovered a way would be found to cancel this out and the true value of
the cosmological constant would be zero.

​But then​
 just a few years ago it was observed that the universe is not just
expanding but accelerating, so now theoreticians must find a way to cancel
out, not the entire cosmological constant, but the vastly more difficult
task of canceling it all out *EXCEPT* for one part in 10^120. There are
only about 10^90 atoms in the observable universe.
​ Nobody has a clue how to do this.​


 John K Clark

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