Understanding Expansion of Space

[Zachary Markham]

So what I don't get about the expansion of space, and what I'm assuming one of you can explain to me, is that it seems like if space were expanding, how would we have any way of noticing it? It seems like as the distances between particles expands, so must the size of the particles themselves and proportionally, so would
the speed that they could travel through
said space, so how would we have any
way of measuring or noticing this
occurrence? And I get the redshift and
other evidence for it but there is a clear
contradiction in my understanding of it
and I would be ecstatic if someone could
explain this fully for me.

 

[phinds]

No, particles (and in fact anything smaller than a galactic cluster, which is HUGE) do not expand as the universe expands. Google "metric expansion" and check the link in my signature.

 

[Chalnoth]

Or, said another way, the expansion is a gravitational effect that only impacts the universe on large scales. Things smaller than a supercluster of galaxies generally don't expand (this drops out of the equations when considering what happens with a universe that has some locations that are more dense than others).

 

[Zachary Markham]

Okay what I was able get so far, is that the forces affecting particles and thus the particles themselves do not expand spatially, but how could space expand without the forces that occupy and are defined by space also expanding? It seems like you all are saying that the four fundamental forces only listen to some sort of absolute space independent of the rest of space that we observe expanding, which is absurd.

 

[Zachary Markham]

This contradiction has been unsolved in my understanding of physics for a long time, maybe if someone explained the whole thing from the bottom up?

 

[Chalnoth]

Okay what I was able get so far, is that the forces affecting particles and thus the particles themselves do not expand spatially, but how could space expand without the forces that occupy and are defined by space also expanding? It seems like you all are saying that the four fundamental forces only listen to some sort of absolute space independent of the rest of space that we observe expanding, which is absurd.

The forces expanding doesn't make any sense. Again, the expansion is an effect within General Relativity. The forces stay the same. There is no contradiction, because metric expansion has precisely zero impact on the forces.

 

[Zachary Markham]

Yes, perhaps I should explain my reasoning behind the forces expanding. Photons for example, are responsible for electromagnetic interactions. I am just an amateur but it is my understanding(which may be incorrect of course, that's why I'm here)that In order for particles to interact through electromagnetism, photons must be exchanged between the particles, photons occupy and travel through space, so as space expands, it would seem like the range, and effect of the photons would expand with it, along with the particles responsible for all the other forces. And I don't mean to say that there's a contraditiction in modern physics, simply that there is a contradiction in my obviously false understanding of it. I wish to identify and correct that, which is why I'm here.

 

[Chalnoth]

Yes, perhaps I should explain my reasoning behind the forces expanding. Photons for example, are responsible for electromagnetic interactions. I am just an amateur but it is my understanding(which may be incorrect of course, that's why I'm here)that In order for particles to interact through electromagnetism, photons must be exchanged between the particles, photons occupy and travel through space, so as space expands, it would seem like the range, and effect of the photons would expand with it, along with the particles responsible for all the other forces. And I don't mean to say that there's a contraditiction in modern physics, simply that there is a contradiction in my obviously false understanding of it. I wish to identify and correct that, which is why I'm here.

An expanded photon is just a photon with less energy. It changes nothing about how the electromagnetic force behaves.

And again, the expansion is just an average effect. When you take into account the fact that the universe isn't completely smooth, you get zero expansion for gravitationally-bound systems (i.e., anything smaller than a supercluster of galaxies, as I mentioned above).

 

[Drakkith]

Yes, perhaps I should explain my reasoning behind the forces expanding. Photons for example, are responsible for electromagnetic interactions. I am just an amateur but it is my understanding(which may be incorrect of course, that's why I'm here)that In order for particles to interact through electromagnetism, photons must be exchanged between the particles, photons occupy and travel through space, so as space expands, it would seem like the range, and effect of the photons would expand with it, along with the particles responsible for all the other forces.

First and foremost, the exchange of photons in an interaction is an exchange of virtual photons. Virtual photons are not real photons like you see from a light bulb. They don't travel through space and the don't even exist for any meaningful amount of time. So no, the range and strength of the EM force does not change as space expands.

Also, you seem to be thinking that space "drags" objects along with it as it expands. This is not an accurate way of looking at it. The expansion of space is a change in geometry that makes the distance between objects increase over time unless they are bound together by some force. No new space is being created nor is space moving since space isn't a physical object.

 

[Torbjorn_L]

It is a good, recurring question. Here is my limited understanding, having studied neither general relativity nor quantum field physics but having a general interest in cosmology:

Cosmology is currently understood by the use of semiclassical physics.

- The classical stands for non-quantum physics, and that is how general relativity (GR) is understood.

- The semi stands for quantum physics modifying it slightly.

Here GR is kept weak (low gravitational energy densities) and so called quantum field theory is used to describe the other particle fields. And so they also describe forces, who are just bosonic particles such as the photons of quantum electrodynamic field theory.

The particle fields constitute the particle physics vacuum. So here we have free-coupled it from GR. We don't have to consider the effects of GR on particles or forces, nor the effects of particles and forces as such on GR. (GR of course connects gravity and spacetime with particles and forces in the spacetime considered through mass-energy and pressure/strain considerations, it is what it does. But that is as far as it goes.)

The result is that you can expand spacetime at will, without the vacuum and especially here forces changing character. :w An example is the semiclassical model of so called LCDM cosmology, our current cosmology.

The scale where gravitational (and EM forces, i.e. mainly chemistry) will keep objects together is immense. And the effects are locally small. The current expansion of the universe is ~10^-10 parts/year in every direction.

You will have to go out to scales of 10 000 light years (ly) to see an expansion of 1 ly over 1 million years. The Milky Way is ~ 10 000 ly thick measured over the disk. As it happens galaxies have strong enough gravity to keep together indefinitely anyway.

By looking at spectral lines, that the properties of the vacuum including force behavior stays constant, has been checked to billions of light years. That means most of the observable universe and most of the elapsed time since the current universe emerged.

Also GR has been checked similarly, showing further that the underlying semiclassical approximation is viable and predicting what is seen.

 

[D2Bwrong]

Consider that space isn't expanding but is being created. If one takes two hydrogen atoms and combines them we get a single helium atom. With fusion reactions we reduce the amount of space taken up by two atoms and place the matter in the space of 1 atom thereby creating (freeing) space. Thus stars get smaller (occupy less volume) so the distance between their outer regions get further apart. Every day the sum of atoms in the universe gets smaller but the gravitational affects remain constant.

 

[PeterDonis]

If one takes two hydrogen atoms and combines them we get a single helium atom. With fusion reactions we reduce the amount of space taken up by two atoms and place the matter in the space of 1 atom thereby creating (freeing) space.

This is not necessarily true even as a description of what happens locally in a fusion reaction; but even if it were true, it would have nothing to do with the expansion of the universe.

Thus stars get smaller (occupy less volume) so the distance between their outer regions get further apart.

To the extent this even happens (see above), the effect is miniscule; but in any case, as above, it has nothing to do with the expansion of the universe.

 

[D2Bwrong]

Space itself doesn't exist. Space is a measurement the same as time. Space doesn't mean void. The ancients didn't understand air was composed of atoms and molecules because they couldn't see them - only felt the effect of air moving and saw the results. We don't see space but can see the results. For instance, why does gravity alone fail to predict star velocities at the outer regions of the galaxy? Galaxies and the stars within them move at tremendous speeds. What are the propulsion mechanisms and limiting factors associated with their movements? If we consider energy produced by stars, galaxies, etc. causing "space" to expand then we might assume that the expansion can reduce the limitations that exists. If so then the galaxies at the edge of the universe may well be traveling beyond the speed of light essentially being pushed faster than the propulsion from energy it generates by the expansion behind it.

 

[Chronos]

Were you to paint an ink drop on a rubber sheet then stretch it, the dot would expand. If you looked at the dot under a microscope, you would see tiny unexpanded dots of ink with spatial separation. That is like the universe, the tiny unexpanded dots are galaxies and galactic clusters, the spatial separation represents the expansion of the universe.

 

[Drakkith]

If so then the galaxies at the edge of the universe may well be traveling beyond the speed of light essentially being pushed faster than the propulsion from energy it generates by the expansion behind it.

A couple of things here. First, far away galaxies are already receding from us (and we are receding from them) at a velocity greater than c. That's nothing special.

Second, your description of expansion and energy is incorrect. No energy is generated from expansion. If anything expansion reduces energy in the universe through redshift, but that topic is actually very complicated, non-intuitive, and nuanced, and I couldn't hope to begin to explain it well. In addition, there is no "behind" in this expansion. From the point of view of a far away galaxy, everything else in the universe other than a few nearby galaxy clusters is moving away from it while it itself remains stationary. Which is exactly what we see from our own point of view. All observers, regardless of their location in the universe, would see this exact effect as long as they remain at relatively low velocities with respect to the CMB frame.

 

[D2Bwrong]

A couple of things here. First, far away galaxies are already receding from us (and we are receding from them) at a velocity greater than c. That's nothing special.

Second, your description of expansion and energy is incorrect. No energy is generated from expansion. If anything expansion reduces energy in the universe through redshift, but that topic is actually very complicated, non-intuitive, and nuanced, and I couldn't hope to begin to explain it well. In addition, there is no "behind" in this expansion. From the point of view of a far away galaxy, everything else in the universe other than a few nearby galaxy clusters is moving away from it while it itself remains stationary. Which is exactly what we see from our own point of view. All observers, regardless of their location in the universe, would see this exact effect as long as they remain at relatively low velocities with respect to the CMB frame.

If I mislead you I apologize. I'm implying that energy is driving the expansion and has been for ? billions of years. One must consider that tremendous acceleration began just after the time of the "big bang" and continued henceforth. Even small increments over the life of the universe will result in very large velocities. I am concerned about the measurement of distances which I may comment on in another topic since it is more related to gravitational lensing.

If one considers to be located at the edge of the universe and continuing in an outward direction above c, then a universe wouldn't exist at that reference frame. One would be invisible since light couldn't catch up if one holds c as the speed of light in a vacuum. Thus to see the universe one must be a part of its past

Consider that "behind" implies two motions are occurring co-linearly in a specific sequence of which behind refers to the lagging occurrence.

 

[phinds]

@D2Bwrong, your statements are not being posed as questions, they seem to me to be statements of personal theory based on misconceptions of cosmology. You would do well to read up on some basic cosmology before posting such unsupportable claims further, as personal theory do not go over well here.

Asking whether or not your beliefs are true is one thing, but posting them as fact when they are simply misconceptions is not a good idea.

First, there IS no "edge of the universe". Second, as Drakkith has already pointed out, there are galaxies withing the Observable Universe that are receding from us (with no proper motion involved) at much greater than c but their light still reaches us and they most certainly do exist.

 

[Jonathan Scott]

I like the simple analogy of the universe being like a cone, where the distance from the point is time and space is around it. If you move away from the point, space as a whole gets bigger. However, it doesn't get bigger locally. If you draw parallel lines on it, they remain parallel (as a cone can be made of flat paper). However, if you follow the paths of points which are spread out evenly around a circle, then as they move away from the point they get further apart.

 

[Drakkith]

I'm implying that energy is driving the expansion and has been for ? billions of years.

We already have ideas about how expansion started and why it has accelerated over time. There's no need to propose your own ideas.

If one considers to be located at the edge of the universe

There is no known edge and there is unlikely to be one, especially the kind of edge you are imagining. Far away galaxies are not speeding off into empty space.

 

[tgarcia39]

The forces expanding doesn't make any sense. Again, the expansion is an effect within General Relativity. The forces stay the same. There is no contradiction, because metric expansion has precisely zero impact on the forces.

Yet Einstein believed the U. was statc, until Hubble contadicted that. Was it General Relativity? I thought the expansion was explained by the Big Bang Theory (BBT).

 

[tgarcia39]

An expanded photon is just a photon with less energy. It changes nothing about how the electromagnetic force behaves.

And again, the expansion is just an average effect. When you take into account the fact that the universe isn't completely smooth, you get zero expansion for gravitationally-bound systems (i.e., anything smaller than a supercluster of galaxies, as I mentioned above).

The expansion is of space, not of matter and energy, which amounts were set by the contents of the singularity and are therefore conserved.

 

[tgarcia39]

Consider that space isn't expanding but is being created. If one takes two hydrogen atoms and combines them we get a single helium atom. With fusion reactions we reduce the amount of space taken up by two atoms and place the matter in the space of 1 atom thereby creating (freeing) space. Thus stars get smaller (occupy less volume) so the distance between their outer regions get further apart. Every day the sum of atoms in the universe gets smaller but the gravitational affects remain constant.

Great thinking, IMHO, D2Bwrong (Dare 2B...?)! it seems you describe why stars burn out. The question is, why are the galaxies moving away from us at speeds continually increasing? To me, that means the U. is expanding, but not necessarily space, as you also suspect. I contend, however, that space did not come out of the BB, instead, the BB occurred in and emptied the contents of the singularity into space - and not into a Great Void (GV) as the BBT proposes. The idea of a GV is one of desperation that simply shows the mind has an unlimited capacity for new ideas even when backed into a corner. BTW, the word you used, "affects," should be, "effects." Your thinking is sound; let no one deter you from learning more. Like me, you will be very happy with both learning and the way you think.

 

[tgarcia39]

Were you to paint an ink drop on a rubber sheet then stretch it, the dot would expand. If you looked at the dot under a microscope, you would see tiny unexpanded dots of ink with spatial separation. That is like the universe, the tiny unexpanded dots are galaxies and galactic clusters, the spatial separation represents the expansion of the universe.

If you stretched the sheet before the ink dried, the ink could flow and expand. I jest, but only because the bread rising in the oven is better suited, IMO, to explain expansion.

 

[PeterDonis]

Was it General Relativity? I thought the expansion was explained by the Big Bang Theory (BBT).

The Big Bang Theory is based on General Relativity.

The expansion is of space, not of matter and energy, which amounts were set by the contents of the singularity and are therefore conserved.

This is not correct. First, "expansion of space" is not a good description, as previous posts in this thread have already discussed. Second, there is no sense in which the "amounts" of anything were set by "the contents of the singularity".

The question is, why are the galaxies moving away from us at speeds continually increasing? To me, that means the U. is expanding

No, the universe expanding just means distant galaxies are moving away from ours. The speed continuously increasing means accelerated expansion, which is not the only possible kind of expansion; the accelerated expansion is why dark energy is included in our best current model.

I contend, however, that space did not come out of the BB, instead, the BB occurred in and emptied the contents of the singularity into space

This is not correct. See above.

I strongly suggest that you learn a lot more about our current cosmological models before trying to post again. Ned Wright's cosmology FAQ and tutorial would be a good start:

http://www.astro.ucla.edu/~wright/cosmolog.htm

 

[Drakkith]

Great thinking, IMHO, D2Bwrong (Dare 2B...?)! it seems you describe why stars burn out.

He has not. Stars burn out because they run out of fuel.

I contend, however, that space did not come out of the BB, instead, the BB occurred in and emptied the contents of the singularity into space - and not into a Great Void (GV) as the BBT proposes.

That is not what the BBT proposes. There is no "great void" anywhere in the big bang theory. The theory doesn't mention anything before the singularity, and the singularity itself probably shouldn't be treated as a valid prediction anyways. It's a well known fact by cosmologists that if you take what the big bang theory says back to a certain point in time your math blows up and stops working. That's all a singularity is, a failure in the math to work. Singularities exist in many areas of math and physics, not just in cosmology, and and are usually a sign that your model or theory simply doesn't work given the conditions you've set at that point. For the cosmological singularity it is believed that a better knowledge of physics at the extremely high energies and density of the very early universe would avoid it.

 

[Anarion]

What if the whole thing is just an illusion created by a space-time effect we do not understand?
For instance, looking into a sphere of glass with bubbles and flecks of glitter perhaps (simulating density of time-space). Could you precisely calculate their position?

Just a novice.

Brian

 

[PeterDonis]

What if the whole thing is just an illusion created by a space-time effect we do not understand?

We have no way of evaluating this possibility because it doesn't make any predictions that we can test.

 

[Anarion]

Everyone argues that space-time is flat or curved. What is it is like swiss cheese? Warped in ways we cannot see from a single vantage.

 

[Anarion]

By the way, I cannot wrap my head around the Big Bang Theory. A singularity by definition would be symmetrical. How do you explain a sudden explosion that would result in a chaotic background radiation pattern?

 

[Anarion]

Please forgive my lack of knowledge on this subject.

 

[phinds]

By the way, I cannot wrap my head around the Big Bang Theory. A singularity by definition would be symmetrical. How do you explain a sudden explosion that would result in a chaotic background radiation pattern?

No, a singularity would, as has already been explained, be "the place where the math model breaks down". How you leap from that definition to a statement that it would be symmetircal, I do not understand.

 

[Anarion]

No, a singularity would, as has already been explained, be "the place where the math model breaks down". How you leap from that definition to a statement that it would be symmetircal, I do not understand.

So if I understand correctly, a singularity would contain all the information of a prior Universe?

 

[Drakkith]

By the way, I cannot wrap my head around the Big Bang Theory. A singularity by definition would be symmetrical. How do you explain a sudden explosion that would result in a chaotic background radiation pattern?

That's not how the big bang theory describes the very early universe. The CMB was the result of the universe become transparent after recombination, allowing light from the hot gas and plasma to finally propagate freely throughout the universe. The theory also says nothing about any singularity. That's simply the point that the model of the universe stops working, similar to how 1/x stops working if you try to insert 0 in for x. Whether a physical singularity actually existed at t=0 is unknown.

See post #25 in this thread and this article: https://en.wikipedia.org/wiki/Cosmic_microwave_background

So if I understand correctly, a singularity would contain all the information of a prior Universe?

No, not at all. A singularity is something in math where the rules suddenly break down. Like dividing by zero. You cannot get any useful information out of a singularity.

Everyone argues that space-time is flat or curved. What is it is like swiss cheese? Warped in ways we cannot see from a single vantage.

I understand that you are interested in the big bang theory and space and all, but we have rules in this forum which do not allow personal speculation. If you want to learn about the big bang theory then feel free to stay and to ask questions. If you want to propose ideas such as the one quoted, then you will need to find another forum. PF exists to teach people about mainstream physics, not to evaluate personal ideas.

 

[phinds]

So if I understand correctly, a singularity would contain all the information of a prior Universe?

You continue to avoid actually listening to the definition. As Drakkith has explained once again, "singularity" is just a word that stands for a longer phrase. That phrase is "the place where the math model breaks down and tells us NOTHING". You need to stop thinking of the "singularity" as standing from something real. Now it is true that SOMETHING was going on at t=0 but we have no idea what and "singularity" is just a word that expresses that lack of knowledge.

 

[rootone]

So if I understand correctly, a singularity would contain all the information of a prior Universe?

A singularity is not a physical object, it means conditions exist which our best theories and models cannot sensibly describe.
Like infinite density and zero volume, Infinite curvature, but zero distance.
Yes that means our models are not perfect and we don't know what is happening in extreme circumstances that we cannot observe.
However, engineers design a bridge using Newtons laws.
Using general relativity, accepted to be more accurate, would not result in a better bridge and would be needlessly time consuming.

 

[Monsterboy]

http://wmap.gsfc.nasa.gov/universe/bb_cosmo_infl.html
I need someone to clarify the below point on the drawbacks the Big bang theory

•The Horizon Problem:
distant regions of space in opposite directions of the sky are so far apart that, assuming standard big bang expansion, they could never have been in causal contact with each other. This is because the light travel time them exceeds the age of the universe. Yet the uniformity of the cosmic microwave background temperature tells us that these regions must have been in contact with each other in the past.

Have we really found out any distant galaxies or clumps of matter which satisfies the highlighted point ?

 

[phinds]

http://wmap.gsfc.nasa.gov/universe/bb_cosmo_infl.html
I need someone to clarify the below point on the drawbacks the Big bang theoryHave we really found out any distant galaxies or clumps of matter which satisfies the highlighted point ?

I don't understand your question. As far as I am aware ALL distant galaxies (when you go out far enough) satisfy the bolded statement so why would you ask if any do? In what way do you see this as a drawback to the Big Bang Theory?

 

[Monsterboy]

I don't understand your question. As far as I am aware ALL distant galaxies (when you go out far enough) satisfy the bolded statement so why would you ask if any do?

You mean we have observed galaxies so far away that they simply could not have been together 13.7 billion years ago and yet we stick to the model because we have no other choice right now ?

 

[Monsterboy]

In what way do you see this as a drawback to the Big Bang Theory?

It is given as one of the drawbacks in the link i provided.

 

[Monsterboy]

Oops sorry I messed up, I didn't read the whole page the later part of the page does explain how inflation theory does get rid of the drawbacks.

 

[rootone]

Inflation is the most popular explanation for this discrepancy,
https://en.wikipedia.org/wiki/Inflation_(cosmology)
The idea works well, but however it's still really just a hypothesis.
Maybe future technology will allow us to see further back in time than the CMB, and then the hypothesis might be validated.

 

[phinds]

You mean we have observed galaxies so far away that they simply could not have been together 13.7 billion years ago

We observer the CMB and observe its uniformity to 1 part in 100,000 and draw the inescapable conclusion that things farther away than the most distant galaxies we can observer must have been in contact at some point to reach such amazing thermodynamic equilibrium.

and yet we stick to the model because we have no other choice right now ?

No, we stick to the model because it explains all available evidence. That's what we always do in science. Inflation is considered the most likely way for the thermodynamic equilibrium to have occurred but since the Big Bang Theory does not start until AFTER inflation, the fact that inflation is not an establish fact has no impact on the BB Theory.

 

[Monsterboy]

I got confused with the terms "The Big Bang theory" and "Standard big bang theory " , only the former includes inflation right ?

 

[phinds]

I got confused with the terms "The Big Bang theory" and "Standard big bang theory " , only the former includes inflation right ?

No, as I specifically stated, the Big Bang Theory starts at the end of inflation (assuming it even existed) and goes from there. I don't understand the distinction you are making between two seemingly identical terms.

 

[Monsterboy]

No, as I specifically stated, the Big Bang Theory starts at the end of inflation (assuming it even existed) and goes from there. I don't understand the distinction you are making between two seemingly identical terms.

Yea thanks , all this time I thought inflation theory was the early part of the big bang theory hence all the confusion , well I guess this is what happens when all your knowledge of cosmology comes from science documentaries and website articles.

 

[phinds]

Yea thanks , all this time I thought inflation theory was the early part of the big bang theory hence all the confusion , well I guess this is what happens when all your knowledge of cosmology comes from science documentaries and website articles.

I had EXACTLY the same problem/belief until quite recently when @PeterDonis kindly set me straight, as he so often has to do w/ my uninformed ramblings

 

[Chronos]

Under the laws of thermodynamics, the CMB could never have reached thermal equilibrium across the entire sky without being in causal contact at point in the history of the universe. Inflation solves this problem because the light travel time limit is relaxed. This, however, leads to other sillines like computing the allowable size of the observable universe at the onset of inflation - which fosters the unfounded notion the universe must be finite.

 

[Tom Mcfarland]

I am new to this forum, so please forgive me if I am not behaving properly.
What I read above, regarding the expansion of space, sounds like the insertion
of additional space rather than "expansion". Which is being proposed?

That is, "expansion of space between A and B" would dilate of the path,
including the dilation of any measuring units such as parsecs or light years.
An observer would never notice the dilation.

The "insertion of additional space" between A and B would leave the measuring
units unaltered. An observer would notice the insertion. For example, if the
initial state was "AB" and I insert space to "A B", you notice it. If I merely
type AB using a bigger font (that is, dilate), nothing seems changed.

 

[phinds]

I am new to this forum, so please forgive me if I am not behaving properly.
What I read above, regarding the expansion of space, sounds like the insertion
of additional space rather than "expansion". Which is being proposed?

That is, "expansion of space between A and B" would dilate of the path,
including the dilation of any measuring units such as parsecs or light years.
An observer would never notice the dilation.

The "insertion of additional space" between A and B would leave the measuring
units unaltered. An observer would notice the insertion. For example, if the
initial state was "AB" and I insert space to "A B", you notice it. If I merely
type AB using a bigger font (that is, dilate), nothing seems changed.

Google "metric expansion" and check out the link in my signature.

 

[Drakkith]

I am new to this forum, so please forgive me if I am not behaving properly.
What I read above, regarding the expansion of space, sounds like the insertion
of additional space rather than "expansion". Which is being proposed?

Neither "insertion" nor "dilation" takes place. The distance between objects simply increases over time. Space is not a substance and trying to model it as something that can be created and inserted is... problematic. One might then be required to treat a ball falling to the Earth as the removal or deletion of space between the ball and the Earth.