So I think there is two ways you could do this. You could take your rubber band and place stickers on it which represent galaxies, or you could use a sharpie to draw circles on it to represent galaxies.

When you stretch the rubber band in the first case, only the space between the stickers is expanding, not the stickers themselves. In the second case, everything is expanding.

If the second case were what is happening, the measuring unit would expand the same amount as the distance between the galaxies. This could be happening but it is useless because it would be impossible to measure it, I think.

So correct me if I'm wrong but the theory goes like this:

1) Light emitted from galaxies doesn't interact with space or lose any energy as it travels from its source to the Earth.

2) Light emitted from galaxies is, when it arrives at earth, at a lower energy state than expected (redshifted).

3) A known phenomenon which could account for both 1 and 2 is the Doppler effect, which states that if you throw a ball backwards while driving forwards it doesn't go as fast relative to the ground as if you were standing still throwing it backwards.

4) From 1, 2, and 3, we propose that all galaxies we can measure light from, which are all measured to be at a lower energy state than we would expect, could have been moving away from us when the light was emitted towards Earth.

I just know they've been measuring it for 80 years now and virtually every cosmologist and astrophysicist accepts it as fact. Under our current understanding of the universe, no other explanation works.

I'm not smart enough to debate alternatives.

I'm not trying to debate alternatives in this post, I'm trying to understand what people have understood for 80 years.

Your first assumption is wrong. There is no central point in the universe, it is the exact same in every direction. The explanation for this (bearing in mind that I'm only an interested layman) is the replacement of a exploding central object with inflationary cosmology which holds that there was an enormous expansion before the contents of the singularity were released and the expansion is continuing. This explains the near uniform temperature of the microwave background which would not have had time to achieve that state while obeying the restriction of the speed of light. What is happening is that galaxies are moving away from each other (except, for the time being, the local galaxy clusters) and the farther away from each other the faster they are moving away. 'Expansion', I think, is used because it's the best word available.

Much of the reason for this is not understood and it is unknown if it will continue indefinitely. Maybe it's the vacuum energy of space pushing things apart or the creation of additional space as a result of the workings of the universes' wave function creating more space that is carrying things with it. No one really knows which is why the acceleration observation was so stunning when discovered.

I have no opinion on if there is or isnt a point from which the universe is expanding, or even if it is or isnt expanding--the assumption you're referencing was just an argument or a stipulation.

This doesn't make any sense to me though (that there could be no central point) because it would mean that we are inside something which, no matter where we are in it, things are expanding in all directions. Think about it this way: If you put two empty balloons next to eachother and then start pumping them full of air, they cant both start expanding in all directions because they will start pushing eachother. And you're telling me that if you put two observers, one on earth and another on mars, they will both tell you the universe is expanding in all directions away from them. This, in my opinion, cant be the case. Maybe I currently am of the flimsy opinion that either the universe is expanding away from a point, or the universe cannot be said to be expanding. The two balloons example and the CAD scaling example are too much for me to shake at the moment, although I would very much appreciate if someone could show me otherwise and force me to be corrigible.

It is thought that there was an initial singularity which was a billionth of a billionth of a billionth the size of a proton. For the briefest instant that was the entire size of the universe and what I believe that you think of as the central point. And cosmology might still think that but for the near uniformity of the temperature of the cosmic microwave background radiation. Given the size and age of the universe it couldn't be the case that that temperature could be so uniform if the universe were expanding from a central point. There simply isn't enough time for that to happen.

Inflationary Cosmology explains that space appeared (somehow) at a stupendous speed, absurdly faster than the speed of light. At this point most people would object that nothing can travel faster than light but that restriction applies to light traveling THROUGH space, not to space itself. When the universe reached a certain size of space the matter and radiation contained in the singularity was released into it. That is why there is no central point: Everything showed up at once, as it were.

I don't think it valid to compare what happens inside the universe with w/e happened in the very beginning (which includes 'where the heck did that thing come from?'). Who knows if something is pushing against our universe or if there is any feature that we demonstrate to be true in our universe that can be useful in explaining the origin story.

And, yes, I can be here and you can be in another galaxy billions of light years away and everything will be expanding away from the both of us.

Maybe the universe is social distancinging.


PairTheBoard

I think the balloon thought experiment is sufficient to show that this is not possible.

It is useful to understand that all of our theories from all of our sciences are based on observation of every day life and then expanded outwards from there. For instance, if animals did not reproduce, evolution would not be a valid school of thought--full stop. You cant start with evolution and then work backwards saying that animals must reproduce. If they do they do, if they dont they dont, but it has nothing to do with the theory of evolution, it has to do with our observations of animals.

If a theory requires that two balloons next to eachother can both expand in all directions away from eachother, then you are lucky indeed because all you need is two balloons to show that the theory is incorrect. What you cant do is say that the theory is correct and that what you are witnessing--namely, two balloons pushing eachother away--is incorrect.

What is surprising to me is that, in the 4 numbered statements I gave above, no one assumes that the light loses energy while in travel, especially when that seems to be a completely standard phenomenon, and not doing so would be a one-off.

The redshift phenomenon is only concerned with the energy loss due to lengthening of the wavelength. The wavelegth coming from galaxies gets longer the farther away they are.

You seem to be arguing about real measurements that aren't even questionable. The reasons might be debated, but my understanding is that nothing else can explain the doppler shift in our current physical model.

Also, relativity actually predicts this phenomenon. Observations confirm it.

I'm not sure what I'm arguing about. Honestly I'm mainly arguing to get a better understanding, but that doesn't seem to be happening as much as I would have hoped. If someone tries to rail against evolution they are given a plethora of arguments which make sense and dont appeal to anything contradictory without explanation.

I never really got any responses to the line of reasoning I laid out earlier, so I'm not even sure if that is how the argument for an expanding universe goes. To say it again, this is how I understand it, and I would love to hear if this is incorrect:

I think you are assuming the Doppler effect in your above post (post#36) and then working backwards from there, so for me you are skipping steps.

I'm assuming that the empirical measurements of a Doppler shift that have been recorded for a long time are not mistakes, if that's what you mean. It isn't me that is characterizing the measurements as a Doppler shift, that's how they are reported.

Look, there's two ways to have data regarding doppler shifts, and I will use sound only to make the example easier. 1) Make a doppler shift, e.g. have a race car drive by, and then record this data using a microphone. 2) Get a microphone and record data, without knowing if the object it came from was or was not moving, look at the data, and see if the source could have been moving.

In case number 2, because the data fits a doppler shift does not mean that it was a a doppler shift. I can use my computer and some sound software to engeneer sound that would sound like it came from a car, and that it was the result of a doppler shift. Just because you hear a sound similar to a sound made which, you know from experience, can happen as a result of a doppler shift, does not by any means guarantee you that the sound from an unknown origin is indeed the result of a doppler shift.

This is a reduced down example, but it is meant to prove a point. Namely, it is not possible to start with the axiom that certain data suggests it was the result of a doppler shift and then work backwards from there, and expect anyone to give your work any credit. The fact that data suggests that it is itself a result of a doppler shift is a positive inductive step.

From what I understand, what we are using is things like this:


And drawing conclusions from it. One conclusion humans have drawn from data like the above is that the light which is observed in pictures / measurements like the one above has been redshifted, i.e. the result of a doppler shift taking place. This is a positive inductive step made from data that, as far as we know, has traveled further than any human is possible of even conceptualizing in their heads. To claim the data being a result of a doppler shift as "empirical measurements" is, imo, inaccurate. I'm not saying that it is wrong, just that there is a very big and important inductive step which is taking place that you are apparently brushing over.

I do understand your point.

So far the only possible alternative known is that all mass ( i.e. every atom) in the universe has gotten larger/heavier over time. This was already posted in jest above. It could produce the same lower energy states observed because we are seeing the past when we observe light emitted from distant galaxies. The obvious problem is that it can never be confirmed except by an omniscient observer outside the universe.

If everything gets larger including the rulers, has anything changed? Maybe, but we can never know.

(Edited to correct smaller to larger)

I would assume that there would be hundreds of competing theories that are alternatives that could explain the same data.

For 1, perhaps light gets redshifted as it travels though tons of very weak overlapping gravitational fields over huge distances. Maybe it happens to such an extent that the light is actually blueshifted and the entire universe is contracting to a point which is on the earth, and we got it backwards twice.

For 2, Perhaps early universe light from 12billion years ago was was at a lower energy state by default, but we have assumed the energy of light emitted by distance galaxies is constant over billions of years, so we assume it must be the same now as it was then, and a doppler effect would incorrectly explain this difference in energy.

Perhaps light decays with age much in the same way rocks do from the elements and the universe is not expanding or contracting at all. Eventually, after billions ^ billions of years, light disappears like rocks to dust. This, again, would give data which we would incorrectly describe as the result of a doppler effect and as a result from this, an incorrect expanding universe hypothesis.

To me, it seems that the expanding universe theory might be anthropocentric. We have experienced doppler effects all around us, every day a plane flys over we experience it, and as luck would have it, it happens to correctly describe the universe going out billions of years into the past and billions of light years away from us. And that the vast majority of physicists are quite confident in this answer, despite the fact that as a species we are in our infancy (if not fetal stage) as far as space exploration and understanding is concerned, is surprising to me. I'm trying to think of an analogy in human history but nothing is coming to mind.

As far as serious ones that most scientists haven't dismissed already, there's one. What I described. And it's a useless and unconfirmable one.

This is taken from wikipedia:
So I think my personal belief that physicists and cosmology experts are ... not quite dogmatic but, overly-confident maybe, is unfounded. It appears that physicists and cosmology experts are both willing and able to change their minds as to the current best-suited hypotheses, and that this is happening so frequently that there is no risk of dogma. 20 years in the study of the cosmos is nothing, and it looks like there have been plenty of big changes.

I guess I have never spoken with a physicists or a cosmology expert, and my views of them are based on what I've seen in documentaries, read about in books, and read online. I think i'll change my opinion now to assume that the physicists and cosmology experts have a good (read small) amount of attachment to the currently-held best-practices in the field, and many laymen put an undue (read large) amount of confidence on the beliefs held by experts in the field.

Physicists very strongly believe the universe is expanding because genereal relativity, which has been verified many times by experiment, comes very close to requiring either an expanding or contracting universe. Having a universe in which distant galaxies are not moving either towards or away from us require very high degrees of fine tuning. Observing distant galaxies and seeing that they are redshifted and not blue shifted lets us choose expanding over contracting. This would be true for all points in the universe.

The problem with your balloon example is that you basically have a god like observing position where you can see the entire universe all at the same time. That's not possible in the real universe. One cannot observe what is happening on Earth and a distant galaxy simultaneously. So physicists have learned to ignore what these hypoyhetical god observers that seem to be impossible see and instead focus on models that have been confirmed. There isn't much controversy about an expanding universe in the physics community because of the theoretical requirement of expanding or contracting plus observational confirmation of expanding.

"Let there be light".

But not if I'm in Andromeda. Why?

Gravity. I think you know this already. It's the same reason our solar system isn't expanding. Andromeda and the Milky Way are close enough together that they have a gravitational attraction holding them together. When that happens, the affected bodies become in effect, one system.

The opposite is true.

Put 283 random dots on a balloon. Blow up the balloon a bit. Look at the dots on the ballon. Pick one dot to pay attention to in relationship to all the other dots. Blow up the balloon a bit more. Look at the balloon and the dots (keep track of your chosen dot and its relationship to the other dots). Repeat ad nauseum. Then redo the same thing while paying attention to another dot.

Which one of those dots is in the middle? The one you paid attention to the first time? The second one?

This can work, I agree with you, but this only works when an empty void is being created in the center of all the objects being expanded. What I mean is, if this is what is happening, we would see a empty center about which all the galaxies are moving away from, and as that center of nothingness grows and grows everything is being expanded outwards from it.

So if it was happening as you described, we would predict to be able to find this nothingness center (in the balloon, its the bit filled with air)

I think the balloon thing you quoted still holds though. The example you gave does not fit with any observations, as we do not witness universe expansion as well as a centralized void being created at some point.

The currently-believed expanding universe hypothesis is, imo, impossible and can still be proved such with the two balloons thought experiment. Although its very possible I'm fighting against a straw man here.

It is an analogy that is helpful for you to get your head wrapped around it. The 2d dots on the balloon wouldn't be able to see the middle of the balloon either.

All we "see" is that everything is getting further away and the stuff that is more distant is moving away from us at a more rapid pace.. We can also "see" that everything else is getting further away from everything else and the things that are more distant from each other are moving away from each other more quickly than those things which are closer together. This makes it certainly look like space is expanding, and no one has come along with a competing theory that does a better job of accounting for the observations.

Another helpful thing to wrap your head around that makes the headache go away is that all we have are models of everything. We will always only have models.. Maybe next year we will have a better model that you will find more enjoyable.

Thankfully, if you can't get your head wrapped around it, you can still enjoy a tasty beverage. The universe is expanding slowly enough that you won't need to take the expansion into account when reaching for the glass.