Expanding Space (or 'Do I look fat in these?')

[athon]

Firstly I'd like to excuse myself by saying I'm as much a physicist as a chicken farmer is a dinosaur trainer. I do teach it at a secondary level, and think I have a good grasp...but anything too advanced becomes as faith based as religion for me.

That said, I was pondering this the other day:

We know the universe is expanding, and we understanding that it is space itself that's stretching rather than a separation of matter (as such). Now, we can only perceive this (as I understand it) because we ourselves are not expanding at the same relative rate.

So, in effect, could we see it that we are instead shrinking?

Another question; are we not expanding due to the forces holding us together are stronger than the force (gravity?) making space expand?

Or am I so off track I need a packed lunch and a canteen to find my way back again?

Athon

 

[wollery]

Actually I'd suggest a compass, some heavy weather gear and a weeks rations.

But seriously, if we were shrinking then it would require that the atoms we are made of are also getting smaller, otherwisw we'd have noticed by now. This means that the radii of the orbits of the electrons would have to be reducing, but at the same time they would have to maintain the same energy! Now, if you can work out a way to do that......

 

[Kaon]

Another question; are we not expanding due to the forces holding us together are stronger than the force (gravity?) making space expand?

Or am I so off track I need a packed lunch and a canteen to find my way back again?

Athon

That's pretty much not that far off. Of course we don't know for sure what exactly is causing the accelerating expansion of the universe, but appearantly the electromagnetic forces holding us together (physically) appears to be stronger the the expansion force(s). (The electromagnetic forces are the second strongest of the four known elementary natural forces.)

Your question also reminded me of an exercise I had in an astrophysics course a while ago:

Suppose you were not held together by electromagnetic forces. How long would it take you to grow one cm because of the expansion of the universe? Hint: Apply Hubble's law to your head as seen by your feet (or vice versa).

(That's exercise 15.6 from Frank H. Shu's The Physical Universe: An Introduction to Astronomy.)

That's something to think about. If we weren't held together by the EM forces, we would be growing our entire lives. I wonder what it would be like to live in a universe like that...

 

[athon]

Re: Re: Expanding Space (or 'Do I look fat in these?')

That's pretty much not that far off. Of course we don't know for sure what exactly is causing the accelerating expansion of the universe, but appearantly the electromagnetic forces holding us together (physically) appears to be stronger the the expansion force(s). (The electromagnetic forces are the second strongest of the four known elementary natural forces.)

Your question also reminded me of an exercise I had in an astrophysics course a while ago:

Suppose you were not held together by electromagnetic forces. How long would it take you to grow one cm because of the expansion of the universe? Hint: Apply Hubble's law to your head as seen by your feet (or vice versa).

(That's exercise 15.6 from Frank H. Shu's The Physical Universe: An Introduction to Astronomy.)

That's something to think about. If we weren't held together by the EM forces, we would be growing our entire lives. I wonder what it would be like to live in a universe like that...

By the same reasoning as I was using, we wouldn't notice anything on a macro scale. But we would not see the universe expand, either. I guess it would be noticed as an apparent shrinking of atoms...hence it would just be nuclear forces that would be strong enough to overcome expansion (rather than nuclear and EM).

Athon

 

[Kaon]

Re: Re: Re: Expanding Space (or 'Do I look fat in these?')

By the same reasoning as I was using, we wouldn't notice anything on a macro scale. But we would not see the universe expand, either. I guess it would be noticed as an apparent shrinking of atoms...hence it would just be nuclear forces that would be strong enough to overcome expansion (rather than nuclear and EM).

Athon

Actually, we would probably notice the expansion, because things move apart faster at greater distances, according to Hubble's law. If it weren't for the EM forces, everything would be moving apart at different, and for all we know, life as we know it wouldn't be able to exist in such a universe.

That being said, I want to remind you that there are two nuclear forces: the strong (colour) and the weak. The strong nuclear force is the strongest of them all, followed by EM. The weak nuclear force is the third strongest, i.e. weaker than EM. Therefore if the expansion force were stronger than EM, it would also be stronger than the weak nuclear force.

Another thing to note is that the expansion force isn't necessarily stronger than gravity. Only at large distances where gravity isn't strong enough do we notice that actual objects move apart due to the expansion. For example, the stars in our galaxy aren't moving away from each other due to the expansion. Even the Andromeda galaxy at more than 2 million lightyears away isn't moving away from us (in fact, we're on a collision course with it).

 

[Soapy Sam]

Seems to me (and my grasp of physics probably makes Athon look like Einstein), that "shrinking" and "expanding" are relative ( not relativistic) terms.

If we are shrinking and the atoms which compose us are also shrinking, then the orbital problem goes away. But I would like to know against what standard the shrinkage is measurable.

Athon. Have you been eating mushrooms lately? Seen any white rabbits?

 

[athon]

Seems to me (and my grasp of physics probably makes Athon look like Einstein), that "shrinking" and "expanding" are relative ( not relativistic) terms.

If we are shrinking and the atoms which compose us are also shrinking, then the orbital problem goes away. But I would like to know against what standard the shrinkage is measurable.

Athon. Have you been eating mushrooms lately? Seen any white rabbits?

Good point, and pretty much covers what I was thinking. I guess I was wondering why we refer to the universe expanding, when it could just be that we're all shrinking.

No, this was not after I ate any mushrooms. And neither myself or Harvey the Six Foot White Rabbit have seen any other bunnies hopping around.

Harvey think's that's funny. He's laughing now. Oh, now he's fallen off his chair. Harvey is sooo silly.

Athon
(is it ok to eat the one's with brown spots?)