An expanding universe? Am I expanding?

Originally posted by Hawthorn
If the Universe were expanding wouldn’t everything inside of it be expanding as well? if the universe and everything in it is expanding at the same constant rate we wouldn’t be able to detect it because we would be going in sync with it
You’re assuming the only way to measure something is direct measurements of size. Not true. Redshift, square/cube law, and other effects are still noticeable if you double the size of everything. Your criticism only applies only if you use a simple ruler to try and measure any difference. Remember, the various forces haven’t changed their strengths, and the various ratios of forces and such that govern actual behavior will be affected because of this.

Anyhow, as others have said – the universe is expanding overall, but on a local scale it isn’t, as any expansion is overwhelmed by gravitation and such. Or at least, if it is, it’s to a much much much lesser degree. (Anyone got any numbers on this?)

On the same general topic of “cosmological effects we don’t notice at our scale,” isn’t it true that, for someone standing on the Earth, gravity is slightly stronger at the feet than the head? It would stand to reason, given the inverse square law.

Seems I read somewhere that one’s head weighs slightly more if one is inverted as compared to being upright, something like the equivalent of a drop of water. This might play into the general tenor of the OP, in that it’s a real effect that follows from physical law and is measurable with sensitive enough instruments, but that isn’t perceptible in our normal human frame of reference. Can anyone confirm my faulty memory on this?


I think you’re exactly right about the head/gravity topic. It seems straightforward enough. Along the same lines, if you are at the equator you weigh less (earth bulges slightly, you are further from center of mass), you weigh less on planes, etc. In fact, I do believe our beloved Cecil covered this topic at one time, but I’ll leave it to others to research.

However, I don’t think that your case addresses the topic. I think the question was not in reference to our “normal human frame of reference”. I believe Hawthorn was claiming that even in principle with perfect scientific intsruments, one wouldn’t be able to detect the change, a claim that I disagree with.


The standard of length is a matter of definition. You cannot speak of extent without having some definition to compare it to. In that sense, it is not meaningful to say everything in the universe doubled in size because you have nothing to measure the change against. You could define your unit of length based upon the strength of some field, I suppose, and you could have a consistent definition of length. You have the problem that all of our rulers are invalid after the change. I think it would be more convenient to say our rulers are a constant size and the strength of some field decreased.

You could also define your unit of length so that the universe is not expanding, but constant in size; you would then be forced to conclude that all of your rulers and the solar system are shrinking. You would then need to redefine your unit of time or have the speed of light depend upon the age of the universe.

More convenient is not more or less correct, but it is desirable. We would like to have the speed of light constant and have rulers whose length does not depend upon how old they are.

Great, now I’ve got a Monty Python tune from “The Meaning of Life” running through my head non-stop! :slight_smile:

Expecting Eric Idle to Come Out of My Refrigerator,

The galaxies in the universe are expanding, so I’m told. But wouldn’t this OP require more an analysis of electrons and protons aging and losing mutual attraction at different rates? If they are the same, then there would be no difference in the length of your arm? (I know … you could say the universe gravitational effects relative to the current nuclear attractions have some effect, but this doesn’t seem to play out) Having a hard time understanding the expansion of the universe (galaxies) to the attraction between electrons, protons, polar molecules, etc.?

Blue Muon…you saw me expanding alone, without a glance at my hadron…

As much as I’m wary of becoming unpopular with my first post on the board, I feel compelled to bring up the theory of gravitational expansion.

The first couple posts up there (^) seemed to be heading in this derection. GE suggests that all matter is expanding at a constant rate, and that this expansion is the “cause” of gravity. According to the theory, gravity is not an apparent downward acceleration caused by as-yet-unexplained forces, nor is it caused by curvature of space-time, but rather it is a real upward acceleration of the surface of the earth (and the sun and all stars, planets, and other celestial bodies, as well as me, you, and the corpse of Isaac Newton). We don’t notice this, of course, because our frame of reference is changing at the same rate. (As the computer screen expands, the photons it emits expand, the sensory cells in our retinas expand, and the neurons that interpret the information expand, etc.)

I discovered this theory in a book called The Other Theory of Physics by James Carter; it’s an interesting read. Exerpts can be found at (among other things), especially here and here.

If you don’t feel like believing it (probably a good plan), I recommend it for the pretty pictures and the fact that the author uses the word “ubiquitous” (which is a great word…if only t’were ubiquitous).

So basically, the answer is we don’t notice the universe expanding because our rulers are expanding at the same rate.

I read a book called “Relativity for the Layman.” Seemed pretty good. Can’t for the life of me remember who wrote it, though…

Just skimming that website, I’d have to say it’s not a very reliable source. The simple statement that they are searching for the “truth of physics” is a red flag for pseudoscience.

As previously stated, we can deduce the expansion of space by other means than just putting down a ruler. For example, increasing redshift with increased distance.

I agree. If you were shown some phenomona along the lines we’re discussing, and then asked to explain what had occured, you could say either a,b,c had held constant while d changed, or that b had changed while a,c,d changed. Especially because a,b,c,d are all defined in terms of each other. Is that what you’re saying?

I took the question in a different sense though – if everything doubled, could we detect it? I think the answer is yes. I agree with you in that we might not know whether the size had doubled or our rulers had just shrunk or the speed of light had changed or some comibnation of changes between forces and fundamental units, but we would be able to tell something happened. And I think that denies the claim that “if the universe and everything in it is expanding at the same constant rate we wouldn’t be able to detect it because we would be going in sync with it”

Not to be defensive or anything, but the book seemed legit (the weirdest thing was the author’s obsession with “Max the string demon” who could grow to any size and measure photons and such). I found the website after while searching for more information. I can’t find anywhere that it says it is authorized by the author.

In any case, the fact that it goes against not only Newtonian dogma but also every accepted physics discovery from the 20th century is the best flag for pseudoscience I can see.

Yes, that was my point. You can’t know whether you forces decreased or your rulers go smaller. Rigid rods are usually thought to have constant length. It would be an inconvenient system of length that allowed the length of a ruler to change. The more convinent interpretation is that the rulers stayed the same length and forces decreased.

Gordo You mean like this quote?

I’m a little confused. I thought that when it was said that the universe was expanding, that meant that the galaxies were drifting farther apart (and clusters and super-clusters). I didn’t think that it applied to systems within galaxies (i.e. solar systems, distance from your head to your feet, atoms within molecules, atomic particles within atoms, etc.). My question is: if everything is expanding, then what is NOT expanding? Is the speed of light not expanding? (Which would mean the speed of light is actually decreasing compared to the rest of the universe.) Or, is it that “red shift” thingie that you yahoos are talking about? (And if that is the answer, then how do we know that the red shift isn’t actually shrinking, making it seem like everything else is expanding?)

Someone please elaborate.

Monocracy, the generally accepted theory is that everything is just getting further apart (traveling with the inertia from the Big Bang). There is no actual increase in the size of matter. The theory I brought up (which says matter itself is expanding) is thought to be a load of crap by 99.9% (or more) of scientists. But bear in mind that we don’t really know anything. The apparent property of red shift could in fact be “shrinking,” or it could be due to some other illusion that we haven’t discovered yet. And of course, we could be lost souls living in a fishbowl with carefully regulated properties that gives us the illusion of existing in a larger universe. It’s all possible.

Quoth Monocracy:

You thought correctly. Space is expanding uniformly at all scales, but tiny little things like atoms, people, and galaxies don’t care much about what space is doing, and stubbornly just stay the same size. We were just discussing the fact that even if such things did care, it wouldn’t make much difference.

All these posts are very informative and/or amusing, but I couldn’t find an answer to the more perplexing question of: What’s the universe expanding into???

Welcome to the SDMB!

Short answer: “nothing”, or “it’s not known/understood”

Longer answers from astronomer Dr. Sten Odenwald…

The universe’s expansion is along a spacial dimension that cannot be percieved.

Here it comes again, the old ants on a baloon analogy. The entire universe is the outer surface of a baloon. The baloon is being blown up. We are like ants on the surface. The universe is the surface, and that is all we can directly perceive. We can’t look into the ballon, we can’t look up from the surface of the baloon.

Notice as the baloon expands, any given pair of dots on the surface will get further apart. This is analogous to how galaxies and clusters, etc. drift apart. The same would hold true for smaller objects, but there are other forces that hold those smaller objects together, and these forces are very very very much greater than the force of the expansion.

The balloon’s surface is 2-dimensional, but it is suspended in a 3-dimensional space. Notice that at any point on the balloon’s surface, the expansion is along a spacial dimension that is exactly perpendicular to the surface of the balloon at that point. Likewise, it is thought that we exist in a 3-dimensional space suspended in a 4-dimensional hyperspace, with unperceivable expansion occuring in a similar manner. (Actually, it’s a 4 suspended in a 5 if you include time… which Einstein did.)

Now to your question: What are we expanding into? First, there is no way of knowing, we can’t percieve anything except the baloon. Second, it’s meaningless, the universe is defined as the balloon, there is nothing outside of it – nothing nothing, not even vacuum, it is just non-existent.

Hope this helps.

[steely dan] "This is the day of the expaaaanding man. . . "[/steely dan]