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michel123456

Quibbles with the balloon analogy

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The blowing baloon is a very bad analogy (first page of Princeton article). In the blowing baloon, everything grows, not only space between elements, but elements themselves. Totally confusing. That cancels the explanation of the "Do objects inside the universe expand, too?". Not saying it provoques the question in the first place.

A much better analogy is that of the raisin cake, in which the raisin do not change size.

But even there, the distance between all the raisins increase, not only between the far away raisins. Damned analogies.

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Just put ants on the balloon and be happy that your stars can even move in space now.

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I will try to continue pointing the elements of the article that raise immediate confusion for a not educated but not simple minded reader. Not intended to make a debate, but in order to make clear that such presentation most often conduct into misunderstandings instead of clarifying the subject.

For example, from your link http://www.astro.princeton.edu/~aes/AST105/Readings/misconceptionsBigBang.pdf

 

"Like Darwinian evolution, cosmic expansion provides

the context within which simple structures form and

develop over time into complex structures."

 

Totally unnecessary. Totally confusing at first sight, rebutting. How can structure raise from an explosion (sorry for the word, it has been said, too late to erase),when an expansion intuitively raises disorder. You need tons of books to explain that, there is no need to present that difficult point right in the beginning.


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Worse analogy:

"A good analogy is to imagine that you are an ant living on

the surface of an infl ating balloon. Your world is two-dimensional;

the only directions you know are left, right, forward

and backward. You have no idea what “up” and “down”

mean. One day you realize that your walk to milk your aphids

is taking longer than it used to: fi ve minutes one day, six minutes

the next day, seven minutes the next. The time it takes to

walk to other familiar places is also increasing. You are sure

that you are not walking more slowly and that the aphids are

milling around randomly in groups, not systematically crawling

away from you."

 

Here the reader imagines himself (the ant) upon Earth (the baloon). But Earth is not growing! And the distance to get home from work does not increase. It should be better without analogy.

And continuing with

"Noticing these facts, you conclude that the ground

beneath your feet is expanding." The reader is on Earth, the ground is there. Very confusing.


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Continuing:

 

"The term “at rest” can be defined rigorously." Here the reader is surprised. The few elements he knew about Relativity crumble down. Worse, the reader is so sure of what he has learned, he barely reads the next sentence and closes the link.

Why presenting such a difficult point? IMO unnecessary. You can explain expansion without opening such a debate.

 

And a few words later : "But in Einstein’s general

theory of relativity, the foundation of modern cosmology,

space is dynamic." which contradicts the precedent sentence in the poor reader's mind.


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Continuing playing devil's advocate:

 

"In this sense, the universe is self-contained. It needs neither

a center to expand away from nor empty space on the

outside (wherever that is) to expand into. When it expands, it

does not claim previously unoccupied space from its surroundings."

 

So there is are surroundings! Did you hear that Mr President? I heard that.

......

How difficult to negate something without creating it. The sentence should be entirely rebuild.


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Again;

"in our universe, as on the surface of the balloon, everything

recedes from everything else."

 

Same mistake. Only large intercluster space is expanding. Not everything. Error.


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And here;

"If one imagines running the clock backward in time, any

given region of the universe shrinks and all galaxies in it get

closer and closer until they smash together in a cosmic traffi c

jam—the big bang."

 

A classic in confusion. The reader is supposed just having accepted that small distances, inside a galaxy cluster, never change. And just a few words later you insist in explaining that reversing time, galaxies crush together. If the reader is not a total imbecile, he must wonder what is that for a clarification.


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And here BTW a passage I personnaly do not understand:

"It was like having the surface of Earth and all its highways

shrink while cars remained the same size." Talking about the backward analogy, that is certainly not the image I got from the BBT, I thought matter was created in another stage and that only radiation existed in the first period of expansion.


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Wow

 

"This ubiquity of the big bang" Dangerous words. Ubiquity is reserved to God. Never use such vocabulary into a scientific article.


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You don't want me to continue. IMO very bad article. The drawings are fine.

Edited by michel123456
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I don't see anything useful in this commentary.

 

Can anyone else find something useful in it?

 

Timo answered what seems to be the main objection. Just put ants on the balloon. They will not expand.

 

The balloon analogy of expansion cosmology does not by itself specify what kind of objects one puts on the balloon. Could be pennies, could be raisins, could be ants. Whatever is chosen to represent stable clusters of galaxies is not going to expand.

 

Michel, you seem to be just quibbling---arguing for the sake of it.

 

I don't know where it is appropriate put that kind of thing at SFN. We don't usually do it here.

 

==============

 

Michel, much of what you say is ostensibly a criticism of Lineweaver Davis' excellent Sci Am article of March 2005.

 

But the critique is not substantive. It strawmans the article, quibbles, doesn't connect. Comes across as either lightweight or peevish. Do you really want to keep this critique around or should we dispose of it?

 

For example it is common to say that the BB occurred everywhere. That it was ubiquitous. That's a correct statement about what the standard model says. It had no particular location in todays space. All the space that existed in the early universe around time of the BB participated.

Ubique is Latin for everywhere, ubiquitous is English for everywhere.

 

So what is your objection? You say Lineweaver Davis should not say that the beginning of expansion was ubiquitous because ubiquity is reserved for God. You admonish Lineweaver for that. Give us a break :D:rolleyes:

 

=================

 

The next thing I notice sounds like a Intelligent Design troll talking about the impossibility of biological evolution leading to complex life. The argument from incomprehension.

 

How can structure... [arise]...when an expansion intuitively raises disorder. You need tons of books to explain that, there is no need to present that difficult point right in the beginning.

 

It happens from gravity, very naturally. A nearly uniform gas cloud naturally condenses into cobwebby structure. Computer sims confirm this.

You don't need tons of books.

George Smoot does a good job explaining that in less than 15 minutes.

Google "Smoot TED". The entire video is 18 minutes but he handles early universe structure formation in about 5 or 10.

Edited by Martin
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The ants are held together internally by electromagnetic forces. This overcomes any tendency for the ants to be pulled apart as the balloon expands.

 

Similar things happen to galaxies. The local gravitational attraction overcomes the global expansion. The galaxies are not ripped apart or expanding themselves.


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It happens from gravity, very naturally. A nearly uniform gas cloud naturally condenses into cobwebby structure.

 

The nearly part is important. In the context of cosmology this is the galaxy seeding problem. How from a perfectly uniform early universe can the lumps we see today develop? It is generally accepted that the initial density perturbations arose from quantum fluctuations in the inflaton field. That is the field responsible for inflation.

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Thanks for helping, AJB.

 

I suspect the problem here is not that Michel doesn't understand, it is that HE HAS SOME AGENDA CAUSING HIM TO PRETEND NOT TO UNDERSTAND.

 

If he can't find a flaw in what Lineweaver Davis say, then he will fault the way they say itj! :D

 

"In this sense, the universe is self-contained. It needs neither

a center to expand away from nor empty space on the

outside (wherever that is) to expand into. When it expands, it

does not claim previously unoccupied space from its surroundings."

 

So there is are surroundings!

 

No Michel, they do not say there are surroundings. This is getting boring. They say there are no surroundings.

(and therefore the expansion does not claim space from unoccupied surroundings----since there are none.)

 

Spare us the literary criticism, please.

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My problem with the "balloon analogy" is it expects you to imagine 3-D space as 2 dimensional. My mind just refuses to make that imaginative leap. Space is 3-D and the surface of a balloon is 2-D and the balloon exists within 3-D space. Raisin bread is a better analogy. I prefer the tub of soap bubbles analogy. Each bubble is a universe. Some bubbles are expanding, some are shrinking or popping.

Edited by Airbrush

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My problem with the "balloon analogy" is it expects you to imagine 3-D space as 2 dimensional. My mind just refuses to make that imaginative leap. Space is 3-D and the surface of a balloon is 2-D and the balloon exists within 3-D space. Raisin bread is a better analogy. I prefer the tub of soap bubbles analogy. Each bubble is a universe. Some bubbles are expanding, some are shrinking or popping.

 

But raisin bread has its own problems. A loaf of bread has edges. In order to expand, the parts have to move. I'm not familiar with the soap bubble analogy, but if each bubble is a "universe," it sounds way off, as if different "universes" are "next to each other" in some larger 3d space. What?

 

The problem with any of these, really, is that they're attempting to be pictures of what the universe looks like from the outside. But there is no outside, by definition. To have any hope of really picturing it other than as an analogy, perhaps you just have to think about what it looks like from the inside. Imagine the ant's perspective, and translate that to 3d.

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My problem with the "balloon analogy" is it expects you to imagine 3-D space as 2 dimensional. My mind just refuses to make that imaginative leap. Space is 3-D and the surface of a balloon is 2-D and the balloon exists within 3-D space. Raisin bread is a better analogy. I prefer the tub of soap bubbles analogy. Each bubble is a universe. Some bubbles are expanding, some are shrinking or popping.

 

 

Any and all analogies are going to fail at some level. They are only a way of highlighting some important features.

 

If one really wants to understand the expansion of the Universe then you need to think in terms of general relativity, in particular the FRW cosmologies and the Friedmann equations.

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The biggest problems with the balloon analogy is not that it is 2D; this is just a simplification to make the expansion of the universe comprehensible to us normal humans who cannot think beyond 3D. That the balloon analogy is 2D rather than 3D, well try to imagine an expanding hypersphere in four dimensional space. Good luck with that!

 

 

There some bigger problems with the balloon analogy:

  • It assumes a finite universe. That remains an open question as far is I know.
  • It implies that the universe is embedded in a higher order Euclidean space; that a Euclidean point of view is somehow preferential to a non-Euclidean description.

 

Once again, though, the balloon analogy is just that -- an analogy. It's purpose is to illustrate the expansion of the universe in a way that is easier to grasp than the rather abstract mathematical description.

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...

 

 

There some bigger problems with the balloon analogy:

It assumes a finite universe. That remains an open question as far is I know.

 

I agree. To my mind that is the main problem. To include the infinite case one has to stretch one's imagination to include an infinitely big (but nevertheless expanding) balloon. A tall order:D

 

It implies that the universe is embedded in a higher order Euclidean space; that a Euclidean point of view is somehow preferential to a non-Euclidean description.

 

When I've presented the balloon analogy I usually stress that when you use it you have to concentrate on the surface itself. Ignore the outside, the inside, the rubber, pretend they don't exist.

 

All existence is concentrated on the 2D surface itself.

 

To use the analogy properly, one should think of the surface as NOT embedded in a higher dimensional Euclidean space. The geometry can be described in a purely internal way, from the point of view of a 2D creature living entirely in the surface (for whom no other spatial directions exist besides those lying in the surface.)

 

Including some additional discussion like that can help to offset the drawbacks you mentioned.

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Oach, I was a bad guy writing this kind of comments.

 

It was not on my agenda at first, but it became quite quickly after a few reading of the linked article. So Martin is right.

I don't know if any of you can understand that this kind of article is only suitable for convincing the already convinced. The non-convinced will have in his mind similar thoughts as those I writed down (with very bad preconceptions (parti-pris) from my part as you may have notice). The BBT is not a simple theory. If you want to explain this theory to an ignorant that is not completely stupid, you encounter some problems. An origin that has no center, an expansion of something that do not exist (no aether) into nothing. No border also. A distance that is not a "real" distance (the expansion of space). Receding speed faster than light compatible with Relativity, organisation into an explosion, negative gravity, a.s.o., all maybe explainable phenomenas for well educated men, but difficult to grasp at-once from a layman. My intervention is not intended to demonstrate that the BBT is wrong or right, it is intended to show that the BBT is not easy to explain, and difficult to accept.

Edited by michel123456
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For what it's worth, I found the balloon analogy very helpful when I was an "ignorant that was not completely stupid." Don't speak for everyone. I also find your quibbles pretty bizarre. It's as if you think it isn't an analogy, but that they're literally claiming the universe is a balloon covered in ants...?

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I used to be a supporter of the BBT. Now I fell into serious doubts. I have no other theory to propose, so I am just asking.

For example: about the balloon analogy.

1.Most of balloons analogies don't use ants. They say: draw some spots upon the balloon, inflate the balloon and see how the spots are getting away from each other.

_problem: the spots are growing exactly as the balloon does. It is a wonderful analogy to explain the scale factor, because everything grows, but not good for the BBT . Basically it is not a problem to me since I could accept easily that I am part of the expansion as anything else around me. But that is not the mainstream point of vue. We are not growing with the universe: we have stable dimensions. So we have to improve the analogy.

2.Instead of spots, we put ants upon the balloon. The balloon grows, the ants don't. But ants do observe their world growing (as we do), but everywhere, no matter the distance.

_problem: we have been told that it is not the case. We are not observing the Earth expanding, the solar system is not expanding, the Milky Way is not expanding, even the local cluster in not expanding. Only the distance between the galaxy clusters is growing. So that to remain consitent with the analogy, the ant must be a galaxy cluster.

3.the balloon inflates.

_problem: there is a center, we can draw a vector from the ant to the center. In the analogy, the inflation has a direction, that is not the case in the BBT.

4.the balloon inflates.

_problem: where is the clown who inflates the balloon? A balloon does not inflate from his own resources, there is need for "deus ex machina". The raisin cake is better, no clown necessity.

5. The balloon inflates at an increasing rate (as the BBT), so the ant feels a force (an acceleration).

_problem: we do not feel such a force in real world. Actually, in real world we do feel a force (gravitation) but it is assumed it has nothing to do with the subject.

6. The balloon has a surface, an inside and an outside. Nothing of such in the BBT.

7. The ant lives upon the surface of the balloon, the limit between inside and outside. Nothing of such in the BBT. We should have put the ants flying inside the balloon, but that makes the whole analogy collapse, because the inflation of the balloon has no effect at all about the flying ants. Their distance do not increase anymore and since they went out the surface they live in 3d world, not in a 2d world as presented in the analogy.

 

So we take the raisin cake analogy, much better.

 

Definitly IMO the balloon analogy is not good.

Edited by michel123456

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I would not "throw away" a model because the analogies used to describe features of the model are not completely accurate. You are falling into the trap that a model must be easily explainable in terms of everyday language. I see no reason why a model must be "explainable" in simple terms.

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I used to be a supporter of the BBT. Now I fell into serious doubts. I have no other theory to propose, so I am just asking.

For example: about the balloon analogy.

The balloon analogy is just an analogy -- and it is an analogy used to try to convey the idea of the expansion of the universe to us dumb lay people. Cosmologists do not use the balloon analogy themselves.

 

1.Most of balloons analogies don't use ants. They say: draw some spots upon the balloon, inflate the balloon and see how the spots are getting away from each other.

_problem: the spots are growing exactly as the balloon does. It is a wonderful analogy to explain the scale factor, because everything grows, but not good for the BBT.

Most uses of the balloon analogy talk about points, not spots. Points have zero dimension; they do not grow.

 

2.Instead of spots, we put ants upon the balloon. The balloon grows, the ants don't. But ants do observe their world growing (as we do), but everywhere, no matter the distance.

_problem: we have been told that it is not the case. We are not observing the Earth expanding, the solar system is not expanding, the Milky Way is not expanding, even the local cluster in not expanding. Only the distance between the galaxy clusters is growing. So that to remain consitent with the analogy, the ant must be a galaxy cluster.

It is just an analogy. An easy way to the analogy better is to add an attractive force between the spots (or points, or ants) on the surface of the balloon that diminishes with distance. At short distances, this attractive force will overwhelm the expansion. At longer distances between points on the surface, the expansion becomes large while the attractive force becomes small.

 

3.the balloon inflates.

_problem: there is a center, we can draw a vector from the ant to the center. In the analogy, the inflation has a direction, that is not the case in the BBT.

Forget about the center. Martin already addressed this issue:

When I've presented the balloon analogy I usually stress that when you use it you have to concentrate on the surface itself. Ignore the outside, the inside, the rubber, pretend they don't exist.

 

All existence is concentrated on the 2D surface itself.

 

To use the analogy properly, one should think of the surface as NOT embedded in a higher dimensional Euclidean space. The geometry can be described in a purely internal way, from the point of view of a 2D creature living entirely in the surface (for whom no other spatial directions exist besides those lying in the surface.)

 

 

4.the balloon inflates.

_problem: where is the clown who inflates the balloon? A balloon does not inflate from his own resources' date=' there is need for "deus ex machina". The raisin cake is better, no clown necessity.[/quote']

For crying out loud, the balloon analogy is just an analogy. You are trying to make way too much out of it. The sole purpose of the analogy is to draw lay people out of their Euclidean way of thinking.

 

5. The balloon inflates at an increasing rate (as the BBT), so the ant feels a force (an acceleration).

_problem: we do not feel such a force in real world. Actually, in real world we do feel a force (gravitation) but it is assumed it has nothing to do with the subject.

There is no force to feel. For that matter, we don't feel gravitation, either.

 

6. The balloon has a surface, an inside and an outside. Nothing of such in the BBT.

Once again, forget about everything but the surface. The purpose of the balloon analogy is to get you out of your Euclidean shell. You keep wanting to go back to it. Bad idea.

 

So we take the raisin cake analogy, much better.

Much worse, in my mind. The raisin cake analogy suggests the universe is some lump of stuff in some infinite three dimensional space. One problem with the raisin cake analogy is that invokes the image of the Big Bang as an explosion in space rather than an explosion of space. Another is that it invokes the idea of an ether.

 

 

 

Bottom line: The point of all of these analogies is to help make some of the concepts of modern cosmology understandable to the lay community. You are trying to make too much of them, and in doing so you are missing the key points of the analogies.

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I see no reason why a model must be "explainable" in simple terms.

 

Whatever is well conceived is clearly said and the words to say it flow with ease.(Ce qui se conçoit bien s'énonce clairement et les mots pour le dire viennent aisément.) Boileau (1636-1711)


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You are falling into the trap that a model must be easily explainable in terms of everyday language.
If it is a trap, yes, I am trapped.

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Whatever is well conceived is clearly said and the words to say it flow with ease.(Ce qui se conçoit bien s'énonce clairement et les mots pour le dire viennent aisément.) Boileau (1636-1711)

 

the universe is under no obligation to be easily understandable nor to follow the quotes of a 17th century frenchman.

 

EDIT: a quick google reveals the Boileau character was a poet. he didn't do science or philosophy so it can not be said he was qualified to speak on the matter.

 

it is also likely what he said was in the context of a work of poetry (being a poet and all) in which case, it would be accurate.

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(..)

Bottom line: The point of all of these analogies is to help make some of the concepts of modern cosmology understandable to the lay community. You are trying to make too much of them, and in doing so you are missing the key points of the analogies.

 

My point is those analogies do not help. People who are enough interested in the BBT are not dumb. They may be ignorant or uneducated, but most of them can use their brain. Don't be surprised if your explanation is not always well received when using such analogies. It is much better without analogies at all.

 

For example, you said

An easy way to the analogy better is to add an attractive force between the spots (or points, or ants) on the surface of the balloon that diminishes with distance.

Good. And enough to be understandable, you are talking about gravity. Because if you haid to choose an analogy to " an attractive force (...) that diminishes with distance.", be my guest. What would you choose? An elastic rubber band attached between the ants? No, the force is augmenting with distance. What analogy would you choose?

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michel, the analogies used such as the balloon analogy are only used in the most basic circumstances.

 

where a person comes in with no knowledge of it at all. it is a quick way to get the basic feature over with minimal complications.

 

if you were to try an describe a bus to someone who had never even heard of such things what would you say?

 

i'd probably go with, its like a big truck with lots of seats in the back and people pay to ride it.

 

sure, its not perfectly accurate in every way but it is enough that the person listening would be able to recognise one if he saw it

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The biggest problems with the balloon analogy is not that it is 2D; this is just a simplification to make the expansion of the universe comprehensible to us normal humans who cannot think beyond 3D. That the balloon analogy is 2D rather than 3D, well try to imagine an expanding hypersphere in four dimensional space. Good luck with that!

 

 

There some bigger problems with the balloon analogy:

  • It assumes a finite universe. That remains an open question as far is I know.
  • It implies that the universe is embedded in a higher order Euclidean space; that a Euclidean point of view is somehow preferential to a non-Euclidean description.

 

Once again, though, the balloon analogy is just that -- an analogy. It's purpose is to illustrate the expansion of the universe in a way that is easier to grasp than the rather abstract mathematical description.

 

I don't particularly like the balloon analogy either. I don't think that the

hypersphere is really all that hard visualize. As long as you consider the

balloon model expanding thru time and space creating a sort of pseudo-

space/time representation you pretty much have the hyper-sphere.

It is also a very useful representation of how light has to travel from the

early universe to finally reach us. A cross-section of the hypersphere

shows this quite well.

All that being said, I still have a problem with the traditional BBT.

It seems more likely to me that the universe is cyclical in nature and

expands till energy is mostly gone and there are nothing but heavy elements

left which will combine in a relatively large and no where near infinitely

small density and space and will then go critical after breaking down into

the universal building blocks. Still a big bang but without the faster than

light expansion. Trying to understand what started it all is no doubt a futile

effort. I just don't understand why so many people cling to theories that

predict seemingly outlandish results. I guess everybody is entitled to his

opinion.

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I much prefer the raising bread analogy to the balloon analogy . I vaguely remember being abit confounded when watching Carl Sagan give the balloon analogy (I think it was Sagan . So many others have used the same analogy to date) . If someone hears that 'Matter is made up of mostly empty space' , and that 'space is expanding' , it's understandable that some may jump to conclude that 'Matter may be expanding somewhat too' . For beginners , It's very helpful to know that energy isn't expanding .

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I much prefer the raising bread analogy to the balloon analogy . I vaguely remember being abit confounded when watching Carl Sagan give the balloon analogy (I think it was Sagan . So many others have used the same analogy to date) . If someone hears that 'Matter is made up of mostly empty space' , and that 'space is expanding' , it's understandable that some may jump to conclude that 'Matter may be expanding somewhat too' . For beginners , It's very helpful to know that energy isn't expanding .

 

Rain bread for me to thanks, as you can eat it while thinking about it.

 

But how about the bowling ball on a trampoline analogy for gravity? You actually need gravity itself to make the "analogy" work...and what about the springs around the perimeter? What are they supposed to represent?:mad:

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