The structure of the universe

[Oskiposki]

Hi friends,

 

this is my first post on these forums. I'd like to start a discussion about the different theorys of the stucture of the universe. Is it undboanded, finite, infinite etc. and how would one picture these conceptual ideas.

 

I read in a paper by Albert Einstein: From the latest results of the theory of relativity it is probable that our three-dimensional space is also approximately spherical, that is, that the laws of disposition of rigid bodies in it are not given by Euclidean geometry, but approximately by spherical geometry. From his paper Geometry and experience.

 

I just began to study physics at college (in Sweden, where I live) and so I have not yet aquinted myself with Albert Einsteins theorys so well. I have only read a fiction book called E=mc2 by David Bodanis and it did not give so much insight to the theory as it did to the history behind it. I know a little but not a lot.

 

It would be great if someone could explain what he means by his statement. He also stated in the paper that the world is finite. What does that acctually mean? Could you travel to an end and be stopped by some kind of wall (you get what I mean).

 

What still has to be answerd to for sure know how the world "looks" like. Is it possible?

 

Hope you have patience with my questions and with my spelling.

 

Thank you!

[Tormod]

Welcome to Hypography, Oskiposki.

 

You will find that we have discussed these ideas before, so trawl through our forums and you'll find some older threads about it.

 

But it is certainly something we can discuss over and over so yes, let's pick it up again.

 

E=mc2 by David Bodanis is not really fiction, it is what we label popularized science, since it explains the history behind the theory and why it has the form it has. A couple of good books on relativity are:

 

Michio Kaku, "Einstein's Cosmos: How Albert Einstein's Vision Transformed Our Understanding of Space and Time"

 

Albert Einstein, "Relativity: The Special and the General Theory--A Clear Explanation that Anyone Can Understand"

 

Richard J. Gott, III, "Time Travel in Einstein's Universe"

 

Joao Magueijo, "Faster than the speed of light" (controversial)

 

As for the shape of the universe, there are so many books...I'd recommend any book by the British cosmologist John Barrow, for example "The Origin of the Universe", which, though a bit dated, is a brilliant introduction to his version of the anthropic principle.

[Oskiposki]

Thank you for your fast reply!

 

I will have a look at those books. though I'd like to know what he means with "spherical". ´

 

thank you

[Tormod]

Good question. I would assume that he means that the space has an inherent curvature rather than being completely flat, so that the shortest path between two points in space is a curved line.

 

Whether space itself curves, or if it is spacetime that curves is a matter of debate - I tend to think the latter is more probable. Anyway, curved spacetime would appear as curved space to us since we don't see the 4th dimension (time).

 

Consider what happens when something is in orbit. It automatically follows the shortest path in spacetime, which is the path of least resistance. If it has the correct altitude and speed, it goes into orbit. If gravity did not curve spacetime, there would be no such thing as orbits and thus anything we sent up from the ground would simply keep going straight ahead until something stopped it.

 

Just some quick ideas.

[Qfwfq]

I'd like to know what he means with "spherical".

Actually, according to the brunt of cosmological models, it is analogous to the surface of a sphere except that it's a 3D "surface" of a 4D "sphere", if you can get an inkling of that.

 

You can go round and round Earth's equator, or a meridian, this is following a "staight" path, called a geodetic, and you keep passing where you started. A similar thing applies to the hypersurface of a hypersphere.

 

Welcome to Hypography. :rant:

[Oskiposki]

Thank you Qfwfq. What books treats what you just said? I think I need to read in on this a little more :rant:

[Qfwfq]

Strictly, it's differential geometry but, if you've just bebun to study physics at college, you'll get to that further on. Basically you'll probably start to see analytical geometry in n dimensions soon enough in your courses.

 

In any case, if you're starting physics, don't neglect math!!!!!!!!!!!!!!!!!!!!! :rant:

[UncleAl]

I'd like to start a discussion about the different theorys of the stucture of the universe. Is it undboanded, finite, infinite etc. and how would one picture these conceptual ideas.

One begins science with chair parade. You screw your butt into a chair and read. (Six months in the lab will save you an afternoon in the library). Start with search engines,

 

http://arXiv.org/

http://www.google.com/

http://www.scirus.com/

http://scitation.aip.org/

http://scholar.google.com/

 

Let's begin with the ugly part - nobody knows!

 

http://space.mit.edu/home/tegmark/toe_frames.html

Middle

 

However, we can look and theorize consistent with what we see,

 

http://map.gsfc.nasa.gov/

http://arxiv.org/abs/astro-ph/0403292

http://arXiv.org/abs/astro-ph/0310723

WMAP + Sloane Digital Sky Survey

 

http://arxiv.org/abs/hep-ph/0404175

Dark matter candidates

 

http://nedwww.ipac.caltech.edu/level5/March01/Carroll/frames.html

Carroll on what it all means.

 

http://math.ucr.edu/home/baez/RelWWW/tests.html

Mathematics of gravitation

[Tormod]

Great post, UA.

[EWright]

You'll come to find that Uncle Al has a fascination with screwing things into, and pulling things out of "butts"; particularly Tinkerbell's. Welcome.

[Oskiposki]

It would be very interesting to know what the most agitating question in physics is at the moment and what are the consiquences if you solve them. Maybe I should start a new thread but you all seem so very helpfull. Hopefully I might be able to answer some questions in the future as my knowledge in physics grows.

 

thanks you all

[Tormod]

One of the main problems is unifying all the forces into one single theory, also (misleadingly) known as a "theory of everything". Gravity has so far avoided all attempts for unification, whereas the nuclear forces and EM have been unified via the Standard Model.

 

Another problem is explaining the link between quantum mechanics and gravity, or "quantum gravity". No solution has been found yet.

 

On cosmology there are a host of problems...the flatness of the universe and the accelerated expansion are examples.

[EWright]

One of the main problems is unifying all the forces into one single theory, also (misleadingly) known as a "theory of everything". Gravity has so far avoided all attempts for unification, whereas the nuclear forces and EM have been unified via the Standard Model.

 

Another problem is explaining the link between quantum mechanics and gravity, or "quantum gravity". No solution has been found yet.

 

On cosmology there are a host of problems...the flatness of the universe and the accelerated expansion are examples.

 

So ah, how much might someone pay for one of these elusive "theories of everything?" (solutions to dark matter and dark energy thrown in at no extra cost).

[Tormod]

So ah, how much might someone pay for one of these elusive "theories of everything?" (solutions to dark matter and dark energy thrown in at no extra cost).

 

Since I don't think one exists I would think it has to be infinitely expensive. :rant:

[EWright]

Since I don't think one exists I would think it has to be infinitely expensive. :lol:

 

Sold! :)