Re: Analyse This!


me wrote:
Igor wrote:
me wrote:
Igor wrote:
me wrote:
Tom Roberts wrote:
Ahmed Ouahi, Architect wrote:
More or less reflexively, he dropped into his equations something called the
cosmological constant, which arbitrarily counterbalanced the effects of
gravity, serving as a kind of mathematical pause button.

Books on the history of science always forgive Einstein this lapse, but it
was actually a fairly appalling piece of science and he knew it. He called
it ' the biggest blunder of my life '. "

From today's perspective this was not a blunder at all. Thinking
abstractly, one cannot eliminate from the Lagrangian any terms that
satisfy the symmetries required of the theory (chiefly general
covariance). If one restricts the terms to those with no derivatives
higher than the second, and requires linearity in those second
derivatives, one obtains the Lagrangian that yields the Einstein field
equation, with cosmological constant. It is the simplest non-trivial
Lagrangian that obeys the necessary symmetries.

It is, of course, up to experiments to determine the value of the
cosmological constant. Until rather recently, the value was "quite
small, consistent with zero"; with improved techniques we now measure it
to be nonzero. Einstein originally favored zero, because then the
Newtonian limit comes out correct; with a very small value, however,
deviations from Newtonian mechanics would not be detectable.


Tom Roberts

if it is consistent with zero, who is expanding the universe


thank you for this email

You don't need a cosmological constant to provide expansion. In fact,
Einstein originally used it to pull the universe back together, but

whay, was the gravity not strong enuff?

Not strong enough to maintain a static universe that wasn't expanding.

when the universe was found to actually be expanding,.he discarded it.
Or haven't you been paying attention?

is it pushed from inside or is it pulled from outside?

It's the result of the big bang.

from inside or from outside?

No inside or outside on a manifold. There's just spacetime. The
actual "shape" of that manifold is what has always been debated.


this because there should be more vacum and empty space
outside than it is here inside

Where's this outside that you're talking about? GR models the universe
as an open or closed spacetime manifold. There is no outside.

i tell you what, is somthing bigbang is exploding then
expanding, it does it against the outside

an imploding and contraction does it against inside

dont you know it? where have you been?

You don't know what you're talking about. Tell me where the inside and
outside are on the surface of a sphere. They don't exist. All you
have is the surface. Think of it in those terms. A spacetime manifold
is somewhat analagous to this, except in 4 dimensions instead of the 2
dimensions on the sphere.

thank you for this new e-mail

It's not an email. It's a usenet message.

apparently you make things clear for me,
but still,

this surface to universe analogy went too
far, everybody use it, even reporters and
moviemakers, and obviously thay dont
know what they are talkin aboit

Any analogy can be taken too far. Which is why it's usually better to
stick with the actual equations instead of the analogy. But the
analogy can be very helpful so long as you don't confuse it with the
actual model you're working with.

whay using a 2d surface analoguous to
a 4d manifold

whay not using 3d analogous to 4d

This can be done. It's just that many people have trouble thinking in
3d and find it easier in 2d.



another question I have is about the big bang

if by using powerful telescopes
1. we can detect the primitive bigbang light and radiation
2. we can detect that everywhere in 3D
3. the distance to the bigbang light is increasing because expansion

are we inside the bigbang now?

In a sense. We see the effects of the big bang all around us, but the
temperature of the universe has cooled to just under 3 K.

thanks, now that you agree with inside, then an outside must
exists

Depends on whether you are talking about 3 dimensions of 4. In 3
dimensions, we appear to be inside something, but that space is not the
total picture and is emnbedded in 4 dimensional spacetime, where the

is it a rank 3 tensor with 4 elements?

I don't understand what you're even asking about. The main object in
GR is a rank 4 tensor in 4 dimensional spacetime called the Riemann
Curvature. For more information:

http://en.wikipedia.org/wiki/Riemann_curvature_tensor

universe is a self-contained manifold. No inside or outside. Now, you
might be able to come up with a theory where spacetime were embedded in
higher dimensions, but it would not be GR.

only a holywood filmmaker would do that

No, a physicist or mathematician might do it also. There have been
attempts in that direction, with mixed results.



because if we reverese the expantion, then we have no choice, but
being inside the bigbang

That's called the big crunch, essentially running the big bang in
reverse. It was once thought that it might be the ultimate fate of the
universe if there was sufficient total mass for gravity to overcome the
outward expansion and pull everything back together again. But it
doesn't look like it will happen due to the accelerated expansion that
we now see.

what is better, to expand or to impand?

Impand is not even a word. Why am I wasting my time?

no, you dont, you make things more clear to me, thanks

Well, glad to be able to help. By the way, I think maybe the words you
were looking for were explode and implode.

.