Adrian Baker said:
I'm trying hard to find a decent explanation for someone that an expanding universe doesn't mean that galaxies get stretched out and made bigger; that the planets won't get further away from the sun; that we don't grow bigger etc.
I've googled and searched about but a decent explanation of why expanding spacetime doesn't stretch matter is hard to find - I've tried to explain this to my friend, but he isn't convinced by my arguments... Any decent, authoratative sources on the net, or in easy to access books?
Or can someone here explain it all better than me!
I have absolutely no authoritative sources on the internet, but I've got some reasoning for you! Ironic that, just minutes before I came across this topic, I was thinking about this exact same thing from your friend's perspective. Anywho...
If his argument is that expanding universe causes all existence (i.e. ourselves, the planets, the moons, the stars, the galaxies, etc.) to expand, which would mean that we all become "stretched out and made bigger", as in the planets become more distant from the Sun, as we all expand... Well, then, there's no real basis for any argument on that matter. If that were the case, the results would be impossible to notice, as everything's maintaining the same exact ratio.
For example, say our distance from the Sun would increase threefold over the next 100 years. Following his model, we would all also be larger ourselves threefold over the next one hundred years, which would cancel out that distance, because it'd be impossible to tell and it'd be impossible to notice, thus we wouldn't be expanding at all!... Of course, your friend could just say that we can't notice that we're expanding, from which you can give him a nice slap across the face, because he has zero evidence that, in his model, we're expanding in the first place.
If your friend has any idea what redshift is, then he would understand that, indeed, the galaxies across all directions are moving away from us at an alarming rate, and the universe therefore is indeed expanding! If it were doing this in his theory, it'd be impossible to tell! And, if he doesn't know what a redshift is, I'm sure you can explain it to him rather well. Better yet, you should bring him to this thread (or make a new one, or something, I really have no idea what'd be best) and have him bring up his own arguments and engage in conversation with more people about the topic!
Personally, I find the penny-on-balloon argument rather silly, because that'd be like saying that galaxies are simply one object bound together, isolated from any universe expansion. If that argument were to be more realistic, You'd have to have a penny for every atom as your example, which essentially does nothing.
That's just my two cents, though. I'm really not qualified to stand on my own theories with confidence and without objection, else I'd be an ignorant moron. I mean, I'm halfway through my first class in astronomy, and it's basically gradeschool... And I haven't even take any in physics...
... And it's pretty late...
P.S. Funny that I ended up looking for a good reference point for an oral report I have to give tomorrow (or later today, in seven hours actually) on neutron stars and pulsars (yeah, I know, ridiculously easy, I don't need that pointed out!) and that I ended up joining some Physics Forums, browsing around some random topics, and ending up babbling on about the expanding universe. Heheheh. Okay, back to work now.
