Agent Monkeysee on 22/7/2006 at 09:08
Quote Posted by Microwave Oven
I've had a small thought here: If the universe is expanding, why doesn't matter expand along with it?
That's where things go off the rails for me and I don't understand what's going on. I think there's some postulated local binding effect caused by gravity (and therefore the presence of mass) or space is only expanding on a macro-scale or something but I really don't know.
Quote Posted by Stitch
too late :(
goddammit
Para?noid on 22/7/2006 at 10:24
Quote Posted by Agent Monkeysee
That's where things go off the rails for me and I don't understand what's going on. I think there's some postulated local binding effect caused by gravity (and therefore the presence of mass) or space is only expanding on a macro-scale or something but I really don't know.
Actually I think the problem is that the balloon analogy only goes so far - the inital concept is sound, but it doesn't mean that the matter has to stretch just because the dots on the balloon do. Isn't it like, Andromeda is actually moving towards us (we're headed for a non-destructive collision) despite the over-arching inflationary behaviour of the universe?
Quote:
The <a href="http://en.wikipedia.org/wiki/Andromeda_Galaxy">Andromeda Galaxy</a> is approaching the Sun at about 300 kilometres per second (186 miles/sec.), so it is one of the few blue shifted galaxies.
In fact, and I can't find any suitable material to support this, but if you study those wonderful universe timelines like this:
<img src="http://img95.imageshack.us/img95/4884/800pxcmbtimeline300va2dk5.jpg">
It suggests that matter actually remains constant in scale, but draws further and further apart (as suggested by the redshift of distant stars like what Hubble's Law says). We also have to account for stuff like dark matter and energy which is on the increase, too. At any rate, if we look <a href="http://math.ucr.edu/home/baez/physics/Relativity/GR/expanding_universe.html">here</a>, it supports this idea and suggests, as Monkeybutt said, that due to the "manifold" property of space, we don't notice expansion on a local scale. The Solar System kind of holds itself together by gravity, for instance.
Mortal Monkey on 22/7/2006 at 15:31
Quote Posted by Raven
RE:photons and energy and Mortal Monkey.
I guess from above I conceed that photons can be thought of as "energy" but in the big bang/big cruch contex they are certainly not the ONLY form of energy - and in most situations never are. This is why I was becoming distressed as I tried to follow where photons suddenly appeared in the discussion.
They appreared in an example, because apparantly you couldn't grasp the concept of "many forms of energy" either.
Quote Posted by Raven
- I was talking about in this thread as a whole, many issues that have been addressed by Agent Monkeysee
Well thank you very much for pointing that out
again then. It was really necessary.
thefonz on 22/7/2006 at 18:50
Well I dont really understand what you're all talking about. Quantum physics and all that jive.
However that diagram 'noid posted is cool and I shall hereby use it as my desktop wallpaper.
*saves to desktop and sets as wallpaper*
Cheers.
:thumb:
descenterace on 23/7/2006 at 09:47
IIRC the main difference between matter and energy is that matter obeys the Exclusion Principle and energy doesn't. So I suppose fermions are matter and bosons are energy.
I know a fair bit of the general theory (unfortunately minus most of the maths) but not much about the specifics. There may well be special cases.
* Überdonkey * on 25/7/2006 at 04:46
Well hello again. This may be a strange place to stage
Return to TTLG but since I study physics now, I feel a strong and righteous urge to correct people:
1) Energy and mass (or matter) aren't different categories of "stuff". They're properties of stuff. An electron has both energy and mass, while a photon only has energy.
2) If by matter you mean stuff with mass, then not all matter obeys the exclusion principle. The W and Z bosons, for instance, are hugely massive (see (
http://en.wikipedia.org/wiki/W_boson)). If they weren't, we'd be a lot more radioactive.
3) As far as I know (might be wrong about this one) you don't need extra dimensions to curve space. We could live in a 4D curved universe. In fact, according to classical general relativity, we do. The ants living on a 2D sphere embedded in 3D space could describe their world as a 2D space with a certain topology, without mentionning 3D at all. Extra dimensions are required only if particles can travel along those dimensions.
4) Noid is right about the manifold business. Roughly, a manifold is a space that looks locally like ordinary Euclidian space (no curvature) but may have global peculiarities. One thing, though: if you draw a short straight line, it will still look straight as you "zoom out". You have to draw a long line. Think of drawing short and long lines on a sphere. Only the long one will curve noticeably, since the short one sees only the local structure.
5) Haven't taken an astrophysics course yet, but my understanding of the expanding universe is this: imagine we're on the balloon, and the balloon is inflating. Particles are pointlike: points don't get bigger. Or particles are string-like: strings can stretch, but string tension will shrink them back to size.
Big objects are held together by forces that operate on a given length scale: this scale determines the size of the objects. If space expands, there's more place to push the objects around, but they keep their size because the length scales don't change. If there were no forces objects would inflate with the universe, but as it is forces provide a time-independent length scale.
This thread reminds of (
http://math.ucr.edu/home/baez/bogdanov.html) this mess.
Other than that, well, I don't have the willpower just now to give a status report on my rapidly unfolding life.
Scots Taffer on 25/7/2006 at 05:11
sup uber - what did you think of the animation? :cool:
In some dimension at some point in time, a version of me is hugging a parallel universe version of you.
descenterace on 25/7/2006 at 05:34
Arggh, absolutely correct! Energy is a property of a particle, not an object in its own right! And bosons are force-carriers, not energy-carriers...
Shows how long it's been since I studied Physics.
Ultraviolet on 25/7/2006 at 06:23
Overdonkey: But what is the speed of love?
* Überdonkey * on 25/7/2006 at 14:41
Quote Posted by Ultraviolet
Overdonkey: But what is the speed of love?
.
A low, cautious crawl.
Quote Posted by Scots Taffer
In some dimension at some point in time, a version of me is hugging a parallel universe version of you.
Small comfort that is, as scotsmen in this dimension crowd into Canada, overrun our public services, kidnap our pets, spread lewdness and viscosity. Regarding the animation, Monkeysee is a soldier of truth. For one, real dimensions allow interactions along them, i.e. something at x=2 pushes something at x=3. This multiple timelines idea doesn't allow that. Secondly, two lines intersecting isn't two dimensional. A surface is two dimensional. Two lines is one dimensional because one parameter suffices to give a position (roughly speaking). And besides the whole thing contradicts causalty.
The actual multiverse scenario isn't about extra dimensions, it's simply about extra universes, and there's no way of going from one universe to the other. I think it was proposed to account for the non-deterministic collapse of a wavefunction after a measurement: basically it says Quantum mechanics
is deterministic, because every different possibility occurs (and hence there's no chance involved). It's basically a cop out. This is off hand, though.
