Expanding universe expanding atoms

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!!
 

pervect

Staff Emeritus
Science Advisor
Insights Author
9,442
772
The sci.physics.faq is a good place to start

http://math.ucr.edu/home/baez/physics/Relativity/GR/expanding_universe.html

Unless your friend has the math to understand geodesic motion in detail, it is likely that he will have to accept an argument based on authority. The sci.physics.faq is reasonably authoratitive, and it's _very_ clear in its statement that the universe does not expand.

To quote the FAQ:

If the universe is expanding, does that mean atoms are getting bigger? Is the Solar System expanding?

Mrs Felix: Why don't you do your homework?
Allen Felix: The Universe is expanding. Everything will fall apart, and we'll all die. What's the point?
Mrs Felix: We live in Brooklyn. Brooklyn is not expanding! Go do your homework.

(from Annie Hall by Woody Allen)

Mrs Felix is right. Neither Brooklyn, nor its atoms, nor the solar system, nor even the galaxy, is expanding. The Universe expands (according to standard cosmological models) only when averaged over a very large scale.

The phrase "expansion of the Universe" refers both to experimental observation and to theoretical cosmological models. Let's look at them one at a time, starting with the observations.
 
Thats a handy link Pervect, and it certainly helps explain my point. Thanks :smile:

Anyone else want to add to this? Any links appreciated...
 

Danger

Gold Member
9,564
244
Adrian Baker said:
Anyone else want to add to this? Any links appreciated...
I don't know any links. I can give you my layman's explanation, if it will help to use it on another layman. Think of a couple of beads or something inside a balloon and connected with a thread. If you heat the air, it and the balloon will expand. The beads can't get any farther apart though, because the thread won't stretch. Then substitute interatomic forces and particles for the thread and beads. This is horribly simplistic, but I find that sometimes that's the best way to show a non-scientist something.
 
G

GENIERE

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!!
Well Adrian my knowledge level is probably less than yours, but here’s my take.

In the voids between curtains of galactic clusters, in the least dense expanses of the universe, the energy of the vacuum exceeds gravitational attraction. In the galactic regions with high densities of baryonic and “dark” matter the converse may be the case.
At the universal scale, the clumps are insignificant compared to the voids so I imagine the end is cold, dark, nothingness; another 20 billion years if the “big rip” concept holds water.


...
 

DaveC426913

Gold Member
18,056
1,637
I read about this done with the venerable expanding balloon / expanding universe metaphor.

Take the balloon (the one that represents the expanding universe).
Glue a dozen pennies to it. (galaxies)
Blow up the balloon.
The pennies do not grow, only the space between them.

The expansion of the latex of the balloon (a very weak force) is WAY weaker than the strength of a copper penny.

Thus:

The force causing the universe to expand is simply not strong enough to overcome forces within atoms - or between atoms - or even the gravity between planets - or even the weak gravity between stars within a galaxy. But the gravity between two galaxies is so incredibly weak, that the force of the expanding universe CAN overcome it.

Your friend is overthinking the expansion force. It is not some overarching force that can flout the laws of physics and magically yank an electron away form its proton. It is simply a very weak (if far-reaching) force much like gravity is weak, yet far-reaching. We don't ask why gravity formt he Moon rips electrons away from their protons do we?
 

Danger

Gold Member
9,564
244
DaveC426913 said:
Take the balloon (the one that represents the expanding universe).
Glue a dozen pennies to it. (galaxies)
Blow up the balloon.
The pennies do not grow, only the space between them.
I spent 5 minutes trying to think of some way to make the bead thing work on the outside of the balloon. Never thought of using a solid body like a coin. Good job, Dave.
 
I'll try the pennies, good idea - thanks.

Normally with a balloon, I draw galaxies on with a biro, then blow it up. Unfortunately, this 'proves' my friends point that the galaxies grow too! The pennies should help... but I do think I'm fighting a losing battle here. :uhh:

I've searched the 'net some more, but nothing I can find gives an in-depth analysis of this 'problem'. My friend says that we can't measure the growth of the galaxies, because expanding spacetime changes our measuring equipment too!

Has anyone any good data on 'average distance between galaxies' that are near to us and comparative data for distant galaxies say 10-13 Billion light years away? I know that they are more densly packed at huge distances (less expansion of spacetime), but can't find any data (convincing data!) to back this up.
 
Adrian Baker said:
I know that they (galaxies) are more densly packed at huge distances (less expansion of spacetime), but can't find any data (convincing data!) to back this up.
If you have no convincing data, how do you know?

I consider (not know) expansion to be an artifact of gravity and not of recession until it has been convincingly demonstrated to me otherwise. This would mean that the most densely packed regions of space are within galaxies, and not among them.

By principles of symmetry, galactic distribution would be relatively homogenous and this seems to be supported by observation.

P.S. According to Brian Greene ("The Fabric of the Cosmos", 2004, ch. 8) the balloon analogy dates back to at least 1930.
 
Last edited:

SpaceTiger

Staff Emeritus
Science Advisor
Gold Member
2,931
2
There are cosmological models that do eventually produce a "Big Rip" in which atoms are torn asunder, but it requires an extremely exotic form of energy (the density of which increases with time). "Normal" cosmology will produce pseudo-force that is much weaker than the force binding atoms. For this, Dave's explanation is excellent.
 
Last edited:
SHtRO said:
If you have no convincing data, how do you know?
There are thousands of well known facts and phenomena of which I personally do not have the data to hand to support. That is why I posted the request. For example, I believe that Pluto is locked in a synchronous orbit with it's moon Charon. However, sitting here at my PC I am totally unable to show that either Pluto or Charon even exist - never mind what their orbits are like! Hence my request for help.
 
30
0
Could the supernovae 1a date be explained by other means?
 
X-43D said:
Could the supernovae 1a date be explained by other means?
Could you expand on this for me please X-43D? Is this the evidence that the Universe expansion rate is increasing?
 
30
0
Adrian Baker said:
Could you expand on this for me please X-43D? Is this the evidence that the Universe expansion rate is increasing?
The observations of Supernovae type Ia is the best available evidence for an accelerating universe.
 
X-43D said:
The observations of Supernovae type Ia is the best available evidence for an accelerating universe.
Yes but, how does this help me explain that galaxies aren't being stretched out and made bigger too?
 

Danger

Gold Member
9,564
244
Adrian Baker said:
Yes but, how does this help me explain that galaxies aren't being stretched out and made bigger too?
All that comes to mind here is that the relative abundance of supernovae should be constant, so if a galaxy is not expanding, the distance between events within the same galaxy should not be greater than that of ones in a closer galaxy. On the other hand, I don't know that supernovae frequency is constant over time, and of course you're looking farther back in time as you look farther away in distance. There should be a way to compensate for the difference, though, if there is one.
(I don't really know what I'm talking about here, but I love to help keep the conversation going.)
 
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.
 
Last edited:

jtbell

Mentor
15,323
2,955
Take a look at the date stamps on the previous messages in this thread... Adrian posted his question three years ago! :eek:
 
... Um...

...... Yeahhhh.........

......................Oops?...
 

cristo

Staff Emeritus
Science Advisor
8,056
72
I'm going to close this, since it's so old. Ryan, if you have a question or something you'd like to discuss, please feel free to start a new thread in the relevant forum.
 

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top