The galactic plane

[John Big Booty]

For those interested in Astronomical photos this is a great site.

 

[ajetrumpet]

For those interested in Astronomical photos this is a great site.

found some darn good pictures there, including the famous ones taken by the astronomers!

 

[Lightwave]

Lightwave, as long as we aren't the planetary system on the leading edge

of the expanding "front" (whatever it is), and as long as enough time has passed, what I described

in classical mechanics might be true - now. I won't go so far as to say it was always this way, but

we are no longer in initial conditions.

Further, you have two other comments that need reconsideration (perhaps). First, in M-theory, we

don't have to assume that the big bang was the start of everything. It was just a massive

disruption of our little corner of the universe.

Second, we don't have to assume that there WAS a start. This is a philosophical thing that is hard

for people to accept - yet theists accept an eternal God. Why do you not want to accept an eternal

universe?

I went off and did a bit more research on this and discovered that there's been more work done on the universes shape and what I explained while a valid option is not what has been observed.

From a bit of a search I discovered (like I invented it?!?) that there is a model called the The Friedmann–Lemaître–Robertson–Walker (FLRW) metric* which is an exact solution of Einstein's field equations of general relativity; it describes a simply connected, homogeneous, isotropic expanding or contracting universe. This model has been used by NASA with which to attempt to measure the shape of the universe.

There is a factor in the model which on the wikipedia site is referred to as Omega and depending on whether that factor is positive, zero or negative the geometry of the universe , and thus the shape will alter between an saddle shape (all negative values of omega), a flat universe (zero values of omega) and a spherical shape (all positive values of omega). Each of these universes have observable things that may be measurable. In a spherical universe the angles of a triangle will add up to more than 180 in a saddle shaped universe less than 180 and a flat universe exactly 180.

If the shape of the universe is either saddle shape or flat dimensions will be infinite as per your description and if it is spherical dimensions will be finite albeit in an edgeless living on a sphere surface sort of way.

Well they launched this satellite called the WMAP and they've managed to measure OMEGA and I found this page on NASA which goes into the description and the results.

http://map.gsfc.nasa.gov/universe/uni_shape.html

What I think they've done is that they've measured variation in the cosmic background radiation their closing paragraph on that link states...

"Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know that the universe is flat with only a 2% margin of error."

That's quite a catagorical statement and was updated in November 2009 (not sure if that was when it was posted or the page was updated).

So assuming we are in the 98% then yes you are completely right.(providing existing physics has always held true)

Logically (at least in my intuitive logic which in these kind of things isn't much of a proof) anything infinite doesn't alter in size so if there was a big bang then either it happened infinitely everywhere or it was within a corner - albeit a big one of an infinite area.

So my thought that the big bang created the dimensions doesn't seem to sit well with an infinite space.

If everything did start in a corner of the universe then I imagine you might be able to use classical mechanics to infer a location point if infinite maybe not. Your going to have to do a lot of measuring over a very long time though!

I do note that in some of the reading they stress that the geometry relates to the local geometry which I guess means observable space. So they are leaving a bit of room to back out.

So whatever else at the moment and in our local system everything seems to be flat. Not sure whether they have proof that it has always been like that or not I don't think we know enough yet to answer that question. Certainly I wouldn't be surprised if the local geometry was exactly the same as the wider geometry as there is nothing that I have read either in observations or theory that seems to predict variations in geometry other than through the action of outside forces.

As for the question - Why do I need a start?

I just kind of assumed there would be one... maybe that's where I've been going wrong all along.

Comes to something when you have to reference your posts

* FLRW metric
http://en.wikipedia.org/wiki/Friedmann-Lemaître-Robertson-Walker

 

[LPurvis]

FWIW the quote attributed to Bohr was, I believe, from another source.
Stephen Hawking actually refers to it in A Brief History of Time.


It was a British astronomer Sir Arthur Eddington, an early expert on general relativity.
Allegedly, when a journalist suggested to Eddington that apparently there were only three people in the world who truly understood general relativity.
Eddington paused before replying "I am trying to think who the third person is."

Cheers

 

[ChrisO]

Point taken Leigh…

Here’s another one: -
......single point infinite masses

And another one: -
found some darn good pictures there, including the famous ones taken by the astronomers!

I shouldn’t be so critical but I kind of like the subject the way it is…

Edit to add.
And happy birthday for the other day.

Regards,
Chris.

 

[Lightwave]

Put references into the thread concerning Leighs correction and apologies for all other errors I tried quite hard with the last post to make it as accurate as I could figure.

 

[LPurvis]

Thanks Chris.
I have recovered suitably. As an Aussie you'd perhaps appreciate the midnight BBQ we had upon return from the pub.
(It offered about as much sun as we'd normally get during one anyway ;-p)

 

[The_Doc_Man]

Been busy. Lightwave, I knew about the "shape of the universe" question but was being lazy. Sometimes that happens.

My description of the expansion works NOW but I do not (and did not) claim it to have always been correct. During the original "bang" (whatever it was), non-standard physics abounded. However, given enough time, you lose the relativistic effects and at that point, can use no worse than SLIGHTLY adjusted classical mechanics for descriptive purposes. The slight adjustments are because if two things are speeding away from each other such that classical mechanics would have them exceeding the speed of light with respect to each other, that can't happen. Or can it? The question was never about whether the objects were moving apart that fast, but whether their light would ever be able to reveal that relative motion. To which the answer is no. So even if they really are moving apart that fast, we could never know it.

Some of this stuff is so wildly counter-intuitive that after a while I have to read some good Harry Potter stuff to brush up on my understanding of magic. Often, that makes more sense.

 

[John Big Booty]

Here's a book that may interest some who have posted in this thread.