steveq

Which reminds me, I need a nice hot cup of tea.

SultanOfSwing

Always time for a nice hot cup of tea.

Shard

That is a very cool paper weight.

Was listening to Brian Cox the other day and he was saying that the universe is essentially "flat" (I think). Does anyone know anything about that? I always assumed it would be in some way spherical. With us at the epicentre*.

* Just kidding on that last sentence.

Pulaski

"Flat" in the context of astrophysics just means everything is, more less, evenly distributed in all directions. That said, there are "voids", which are a fascinating topic of study of their own - with the Bootes void being the largest of them, which is a staggeringly large "bubble" (with a diameter of approximately 300million light years) which is virtually devoid of galaxies.

The other thing which has helped me understand and visualize the "shape" of the universe is to think of space as analogous to the surface of a balloon, where everything moves away from everything else as the balloon inflates. The image of an expanding balloon also lends itself to visualizing an allegory of how there isn't a "centre" of the universe away from which everything is expanding.

Shard

The balloon seems de facto spherical to me.

Maybe "flat" is the wrong word to describe "even distribution in all directions"?

Basically, I don't geddit...

I can imagine a "sheet" (plane) that expands with no specific center, but that would be relatively "flat" and then I would wonder why does it need to be 2 dimensional ?
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Hotscot

It's related to special relativity, topology, space time curvature, (what we normally consider spherical/curved), and mass density.
Not really 'flat' as we normally use the term, more of a condition of the universe.

Shard

Ok, that helps a bit.

Pulaski

Agreed, but it is a model to help explain in a way we can easily relate to how three dimensional space appears to be stretching/ expanding. The surface of a balloon is effectively an expanding two dimensional surface (yes, I know a balloon has three dimensions), and it is not easy to visualize an expanding/ stretching volume of space.

steveq

Lizzyq worked out that she was in the same physics lectures with Cox when she read physics and electronics at Manchester around 1986. Doesn't remember him though.

Shard

So she tells you

steveq

She got "mono"/ glandular fever in the first term, so she'd have to be quick.

Pulaski

I was disappointed by the "first picture of a black hole". Despite much apparent excitement in the astronomical community, and several petabytes of data, it was, IMO, nothing more than an orange smudge.

I presume that at that distance stars are usually no more than points of light when viewed from Earth, so to create an image with such width is a technological achievment, but the results are underwhelming.

lizzyq

ALL stars are "no more than points when viewed from earth", without heroic engineering physics, even with our current largest optical telescopes.

and black holes are ipso facto, invisible, so you can't see them in visible light. This "image" was taken with radio telescopes all around the earth and added together with an incredible amount of v computer power to get even this - a technique you can't employ with optical scopes on a large scale, making the imaging telescope 8000 miles in diameter.

It is a technical tour de force, that we have an image, and that the physical reality matches the theory did closely. The brightening at the bottom is predicted by relativity.

HarryTheSpider

I think it's something to do with whether the internal angles of triangles add up to 180 degrees. in a flat universe, they do.

Take a sheet of paper. Draw a triangle on it, using straight edges and stuff. The internal angles add up to 180 degrees.

Now wrap that paper around a large toilet roll. The paper seems curved, but the angles of the triangle drawn on it still add up to 180 degrees. It's flat.

Draw a triangle on the surface of a smooth sphere. The internal angles of that triangle will add up to more than 180 degrees. Not flat.

I think that's it.

I could be wrong. I'moften a figment of mu own imagination - never somebody else's...

steveq

I was going to sketch this, but the best explanation I've found that I can point you at is Laurence Krauss' book
https://www.amazon.com/Universe-Nothing-There-Something-Rather/dp/1451624468