is the universe really expanding ????

[rambo07]

hi
this seems to me like a really stupid question as nearly if not everyone thinks that the universe is expanding ,however i have always had a problem with this and when ever a astronomer says that every galaxy is moving away from us , therefore the universe is expanding i always say to my self how about Andromeda and how about our local group etc ....

We see ,when we look up ,that some galaxies are colliding ,,,,the milky way is a collection of older smaller galaxies which we have picked up along the way ,,,,and when we collect the data of the location of a million galaxies we see a web or filament of galaxies not a random pattern of expansion ...

i would be worried if every galaxy isnt moving away from us because it would mean that we would be the centre of the universe .therefore to me its natural that we see galaxies moving in a different direction ( or away) but how can we ,,(off the cuff) say that for every galaxy that is moving away from us ,,proves that the universe is expanding when we dont know the real direction its taking over time to its relative local group .... most galaxies have nothing to do with our local group or corner of the universe ,they have there own back yard .... our interaction of our own galaxy to our own local group ,,, must be the same for all the other galaxies ....

can anyone say to me that our own local group is expanding ?????

can anyone say that our own galaxy is expanding

can anyone say that our own solar system is expanding ???

please help me out as i dont want to be in a minority of one against the six billion other peeps on this planet

[ToSeek]

Moved from OTB to Q&A, with a redirect.

[ToSeek]

astronomer says that every galaxy is moving away from us , therefore the universe is expanding

I would hope that no astronomer says that "every" galaxy is moving away from us, since that's obviously not true. Space itself is expanding, but local gravitational effects can override it, as with the Milky Way and Andromeda galaxies.

some galaxies are colliding ,,,,the milky way is a collection of older smaller galaxies which we have picked up along the way ,,,,and when we collect the data of the location of a million galaxies we see a web or filament of galaxies not a random pattern of expansion

Again, local effects can override the general expansion, in other groups of galaxies as well as our own. And the web of galaxies we see today matches what models of the evolution of the universe show - there's no contradiction between a "web or filament" and a "random pattern of expansion."

can anyone say that our own solar system is expanding ???

My understanding is that space is expanding everywhere - even inside your body - it's just that at small scales local forces like gravity and electromagnetism override it so we don't notice.

[antoniseb]

[B]... My understanding is that space is expanding everywhere - even inside your body - it's just that at small scales local forces like gravity and electromagnetism override it so we don't notice.

I'd go one step further and say that some systems have scales that are defined by force balance... so the spacing of atoms in crystals is a definite size with no regard to the expansion of the universe, where as orbits and trajectories can be perturbed by expansion, but the tiny scale of change in local space defies our ability to measure it. As ToSeek says, the scale of gravity locally overrides (or perhaps overwhelms) the impact of expansion.

[John Mendenhall]

Try here. All your questions will be answered.

http://www.astro.ucla.edu/~wright/intro.html

Regards, John M.

[John Mendenhall]

Or, more directly, here.

http://www.astro.ucla.edu/~wright/cosmology_faq.html

[rambo07]

Space itself is expanding, but local gravitational effects can override it, as with the Milky Way and Andromeda galaxies.=zero expansion

My understanding is that space is expanding everywhere - even inside your body - it's just that at small scales local forces like gravity and electromagnetism override it so we don't notice.=zero expansion( or we havnt detected or proved it ??)

'd go one step further and say that some systems have scales that are defined by force balance... so the spacing of atoms in crystals is a definite size with no regard to the expansion of the universe, where as orbits and trajectories can be perturbed by expansion, but the tiny scale of change in local space defies our ability to measure it. As ToSeek says, the scale of gravity locally overrides (or perhaps overwhelms) the impact of expansion. = zero expansion

my point is in our local corner ( the same as any other local corner ) if the rate of expansion =zero expansion then if you add all the local corners together you get zero expansion ?????

all you have is normal interaction within a space ,,,, sorry for being super dence can any one show me real proof that expansion is really happening despite local effects ??

[Strange]

i would be worried if every galaxy isnt moving away from us because it would mean that we would be the centre of the universe

(Did you mean you would be worried if every galaxy is moving away? Anyway ...)

We see a very consistent pattern for galaxies outside the local group: nearly every galaxy )and galaxy cluster) we observe is moving away from us. And the further away they are, the faster they seem to be moving.

The simplest explanation for this is that, on very large scales, everything is getting further apart; in other words the universe is expanding.

[Strange]

my point is in our local corner ( the same as any other local corner ) if the rate of expansion =zero expansion then if you add all the local corners together you get zero expansion ?????

Those local areas that are not expanding are a tiny, tiny part of the universe. The space in between them is vast. And that is where the expansion is happening. So the fact that there is little or no expansion in small pockets of space (where the galaxies are) is offset by the expansion happening in the enormous spaces in between.

p.s. could you use the "reply with quote" button to make it easier to see where you are including someone else's words.

[Jeff Root]

Whether space itself is expanding isn't known. What *is*
known is that widely-separated clusters of galaxies move
farther and farther apart from each other. General relativity
describes that as an expansion of space. Everything in the
space (everything in the Universe) is pulled away from
everything else.

But the pull is very, very, very weak. So if there is a force
opposing that pull, the opposing force usually wins. In the
case of your body, the electric forces between atoms and
molecules holds you together against the expansion. The
planets are held to the Sun by gravity, and the stars in the
Milky Way are held together by gravity. The galaxies in any
cluster are held together by gravity. Their mutual gravity
is enough to prevent them from expanding.

However, *if* the expansion *is* something which is taking
place throughout all of space, then it does have an effect
on everything. Orbits of planets around the Sun are very
slightly different from what they would be without cosmic
expansion. It is *very* slight, though, because gravity is
so much stronger than the expansion. The molecules in
your body are slightly pulled apart by the expansion. But
they are affected far, far, far less than the orbits of planets
not only because the distances are vastly smaller, but
because the electric force is vastly stronger than gravity.

In this case, your atoms and molecules don't keep getting
farther and farther apart over time. Planets don't keep
moving farther away from the Sun. Stars and galaxies in
the same cluster don't keep getting farther apart. The
effect is simply to have an equilibrium between expansion
and opposing forces which is different from what it would
be if there were no expansion.

However, if the expansion acts like a force which is
increasing in strength, then eventually the expansion
force could become stronger than all the opposing forces,
and everything would be pulled apart. That is called
the "Big Rip". End-of-the-Universe counterpart to the
Big Bang.

But it is also possible that the expansion only functions
between widely-separated clusters of galaxies. That is the
only place we see the expansion. Even if there is no Big
Rip, it is pretty much guaranteed that eventually all the
distant galaxies will be so far apart that nobody will be
able to see anything beyond their own cluster.

If you're still having a problem visualizing how expansion
can occur on large scales but not on small scales, my
version of the balloon analogy may help.

Imagine a partially-inflated rubber balloon. Its surface
represents a sample of the Universe. Don't worry about
the shape of the balloon. The shape has no significance
in this particular analogy. Sometimes it does, but not
this time.

The Universe is greasy. The balloon is covered with thin
grease. That's okay. We can use it. I have a packet of
metallic sequins. I'll let you sprinkle the sequins onto
the balloon. The grease will hold them in place. Good.
You have pretty much covered the balloon with sequins.
Now I'll blow the balloon up so that it gets bigger.

Ha! The sequins move apart as I blow the balloon up!
Wait a minute-- What's happening??? The sequins are
sliding through the grease, grouping together into little
clumps, and leaving spaces between the clumps! Oh,
right! I forgot. I said the sequins are metal, but they're
also slightly magnetized, so that they attract each other.
Just slightly. But even though the attraction is slight,
it is enough to keep the sequins bunched together as I
blow up the balloon.

-- Jeff, in Minneapolis

[rambo07]

(Did you mean you would be worried if every galaxy is moving away? Anyway ...)

We see a very consistent pattern for galaxies outside the local group: nearly every galaxy )and galaxy cluster) we observe is moving away from us. And the further away they are, the faster they seem to be moving.

The simplest explanation for this is that, on very large scales, everything is getting further apart; in other words the universe is expanding.

yes thats my point ,,,anything not connected to our local group is moving away ,,,but not in relation to there own local group ,,,in other words if you were there in that portion of the universe looking at our group of galaxies moving away from you you would think the same thing that the universe is expanding ,,,my point is that our local group isnt expanding any more than any other local group ,,, when you say that space in between galaxies is getting further apart ,,,well most would wouldnt they as they arnt connected to the same local group ,,,,,, but they are interacting with other galaxies the same as us ,,, to put it another way maybe we need to see how a million galaxies move ,,, within a larger period of time to see if there is a pattern or just a general expansion ,,,to me just a simple observation that most objects are moving away therefore the universe is expanding is a very black and white statement

[Jeff Root]

to me just a simple observation that most objects are
moving away therefore the universe is expanding is a
very black and white statement

The farther apart two galaxies are, the faster they're
moving away from each other. That is true everywhere.
How else would you describe that but "expansion"?

-- Jeff, in Minneapolis

[Strange]

yes thats my point ,,,anything not connected to our local group is moving away ,,,but not in relation to there own local group

Exactly: on a large scale, everything is moving away from everything else (where "thing" means galactic cluster sized things). This implies expansion.

in other words if you were there in that portion of the universe looking at our group of galaxies moving away from you you would think the same thing that the universe is expanding

Exactly: wherever you are you will see everything moving away from you. This implies expansion.

my point is that our local group isnt expanding any more than any other local group

True. But irrelevant. The lampost outside my house isn't getting further away, but that doesn't stop the buses disappearing into the distance.

when you say that space in between galaxies is getting further apart ,,,well most would wouldnt they as they arnt connected to the same local group

And the fact they are getting further apart implies expansion.

but they are interacting with other galaxies the same as us

True. But irrelevant.

to put it another way maybe we need to see how a million galaxies move

I don't know exactly how many have been surveyed but I believe it is a significant fraction of that number. Which implies expansion.

within a larger period of time to see if there is a pattern or just a general expansion

There is a pattern. And it implies expansion.

What does "or just a general expansion" mean? Do you think the universe isn't expanding there is just some general expansion going on?

to me just a simple observation that most objects are moving away therefore the universe is expanding is a very black and white statement

It is not very black and white - it is highly red-shifted

More importantly, science is never black and white. The idea that the universe is expanding is our best theory because it fits all the evidence anc explains so many things. It may turn out to be wrong - but we would need some very compelling evidence.


I don't really understand. You seem to accept that everything appears to be moving away from everything else but somehow don't think this implies expansion. What other explanation is there?

[TooMany]

More importantly, science is never black and white.

Especially in astronomy because you cannot do experiments or control conditions and what you are studying is so far away. Much of what we "know" is based on theories and inferences based on theories used to interpret observations.

I'm not sure that the GR model actually insists that space is expanding uniformly even within concentrations of matter (which must then resist expansion due to other forces). I'm not sure that interpretation is correct, but may rather be a conclusion based on a simplified model in which mass is uniformly distributed in space. This model could lead to a mistaken idea that the expansion is uniform everywhere, regardless of mass distribution. On the other hand, I believe the interpretation of dark energy (as a cosmological constant) is that it expands uniformly everywhere, regardless of mass distribution.

I wonder if we have a GR expert who could clarify this?

[WayneFrancis]

hi
this seems to me like a really stupid question as nearly if not everyone thinks that the universe is expanding ,however i have always had a problem with this and when ever a astronomer says that every galaxy is moving away from us , therefore the universe is expanding i always say to my self how about Andromeda and how about our local group etc ....

We see ,when we look up ,that some galaxies are colliding ,,,,the milky way is a collection of older smaller galaxies which we have picked up along the way ,,,,and when we collect the data of the location of a million galaxies we see a web or filament of galaxies not a random pattern of expansion ...

i would be worried if every galaxy isnt moving away from us because it would mean that we would be the centre of the universe .therefore to me its natural that we see galaxies moving in a different direction ( or away) but how can we ,,(off the cuff) say that for every galaxy that is moving away from us ,,proves that the universe is expanding when we dont know the real direction its taking over time to its relative local group .... most galaxies have nothing to do with our local group or corner of the universe ,they have there own back yard .... our interaction of our own galaxy to our own local group ,,, must be the same for all the other galaxies ....

can anyone say to me that our own local group is expanding ?????

can anyone say that our own galaxy is expanding

can anyone say that our own solar system is expanding ???

please help me out as i dont want to be in a minority of one against the six billion other peeps on this planet

The issue is of scale. Yes all galaxies have what we call "proper motion". This is their motion through space caused by gravitational interactions with other galaxies. This is what we see locally because this is what dominates. Here we are talking about speeds of typically 50km/s up to 600km/s in any directions. That might seem really fast but space is expanding at a rate of 74km/s/mpsec. That is 74 kilometers per second for every megaparsec. As a rough guide a parsec is about 3 light years. So for every light year space expands at a rate of about 2.4cm/s for every light year.

Distance to Andromeda is about .778mpsec away from us. This means just from cosmic expansion it would have a radial speed away from us of ~50km/s. Now its speed towards us is about 111km/s. So gravity locally has a bigger effect then cosmic expansion.

As we look further out the 74km/s/mpsec adds up. At 10 times the distance of Andromeda cosmic expansion starts to completely over take even the fastest moving galaxies. 10 megaparsecs isn't very far in cosmological terms. We are still in our local super cluster of galaxies. Move out to 1,000 times the distance of Andromeda and expansion now dominates. The galaxies still have proper motion to them but the speed at which space is expanding at that point is 50,000km/s. Now we are talking about speeds of over 15% the speed of light. The 50km/s-600km/s proper motion is completely swamped by that. Even if the Galaxy's direction of motion was directly towards us it would be like a fly trying to fly into a hurricane wind. It's not really going to make any bit of difference. And if the Galaxy's motion was perpendicular to us at that distance we'd still wouldn't be able to measure it. It would be like me asking you to measure how fast a person is walking from 100km away. If you have 2 people walking perpendicular to you but on is 10m from you and the other is 1km from you the one 10m from you obviously seems to move further even if they are walking the same rate because we are measuring the angular change in their position.

Now what cosmological expansion does is the opposite of what you think.

It doesn't mean we are at the centre. In fact, with the observations, without cosmological expansion then we would have to be at some centre point. With cosmological inflation tho it only appears that we are some place special but if you do the thought experiment of putting yourself anywhere else in the universe then you see that they see the same type of picture. IE, minus very close objects, everything seems to be moving away from them.

It also solves a problem of how to explain how galaxies can travel at 50,000km/s or even faster then light. You probably know that Special Relativity says no object can be accelerated faster then the speed of light. Well its is a bit more complicated then that. It is more that no information can travel faster then the speed of light. IE objects can't move through space and approach anything else in space at a rate >c. But with cosmological expansion things aren't travelling through space faster then light. It just may be that at sufficiently large enough distances that space is stretching so that the 2 object recede faster then light. Since expansion is completely linear, 74km/s for every megaparsec, all you have to do is get enough distance between you and another objects and all those 74km/s start to add up and you eventually get to a point where the amount of space between the 2 points is > 299, 792.458km/s and thus > light speed.

Now we aren't sure how mass may or may not effect expansion. So it isn't currently possible to measure if space is expanding locally. If it is the rate is far to small for our equipment to tease out of all the motion we undergo from various objects around us. But science will march on and I'm sure some very smart people will figure a way to make measurements that will indicate how expansion is effected by nearby mass if it is effected by it at all.

[WayneFrancis]

I'd go one step further and say that some systems have scales that are defined by force balance... so the spacing of atoms in crystals is a definite size with no regard to the expansion of the universe, where as orbits and trajectories can be perturbed by expansion, but the tiny scale of change in local space defies our ability to measure it. As ToSeek says, the scale of gravity locally overrides (or perhaps overwhelms) the impact of expansion.

This gets to a very technical detail. Expansion wouldn't effect molecular bonds until it hits the binding energy of those chemical bonds then the molecule bond would break. This is because these bonds have to be at very precise energy levels equating to the orbit shell causing the bond, this is my understanding of it. So even if you have a constant energy trying to push the 2 atoms apart it will never do anything until that energy exceeds the molecular binding energy then BAM. With objects that are only gravitationally bound or even statically bound, then expansion would work like a spring system making the distance between objects greater then what would be expected. Probably still to small of an amount to be measured with today's equipment but still.

[WayneFrancis]

Space itself is expanding, but local gravitational effects can override it, as with the Milky Way and Andromeda galaxies.=zero expansion

My understanding is that space is expanding everywhere - even inside your body - it's just that at small scales local forces like gravity and electromagnetism override it so we don't notice.=zero expansion( or we havnt detected or proved it ??)

'd go one step further and say that some systems have scales that are defined by force balance... so the spacing of atoms in crystals is a definite size with no regard to the expansion of the universe, where as orbits and trajectories can be perturbed by expansion, but the tiny scale of change in local space defies our ability to measure it. As ToSeek says, the scale of gravity locally overrides (or perhaps overwhelms) the impact of expansion. = zero expansion

my point is in our local corner ( the same as any other local corner ) if the rate of expansion =zero expansion then if you add all the local corners together you get zero expansion ?????

all you have is normal interaction within a space ,,,, sorry for being super dence can any one show me real proof that expansion is really happening despite local effects ??

It isn't that locally it amounts to zero. It is that locally gravity might cause 2 objects to approach at 100km/s and expansion might push them away at 1km/s leaving the 2 objects still approaching each other at 99km/s.

The problem is how do you tease out the 1km/s? With Andromeda we don't even know enough about its proper motion to say if it is definitely going to collide with the Milkyway yet. It might be on a vector that will have the edges skim each other. We also don't know the mass of the Andromeda and our own galaxy well enough to say how fast the 2 should be orbiting each other. All these uncertainties build up an error bar that is more then we'd expect expansion to be at that distance anyway.

You keep asking for proof. The proof is the red shift data. The proof came first and then through a process of elimination we came to the most likely answer which is space is expanding at a rate of 74km/s/megaparsec and for some reason this rate is accelerating.

[WayneFrancis]

yes thats my point ,,,anything not connected to our local group is moving away ,,,but not in relation to there own local group ,,,in other words if you were there in that portion of the universe looking at our group of galaxies moving away from you you would think the same thing that the universe is expanding ,,,my point is that our local group isnt expanding any more than any other local group ,,, when you say that space in between galaxies is getting further apart ,,,well most would wouldnt they as they arnt connected to the same local group ,,,,,, but they are interacting with other galaxies the same as us ,,, to put it another way maybe we need to see how a million galaxies move ,,, within a larger period of time to see if there is a pattern or just a general expansion ,,,to me just a simple observation that most objects are moving away therefore the universe is expanding is a very black and white statement

But if we look at a distant local group we don't see the objects in that local group expanding away from each other. We just see those objects receding from us.

It is true if you went to one of those groups and look back at us you'd see our local group receding but you wouldn't see Andromeda moving away from the Milkyway.

[WayneFrancis]

...

I don't know exactly how many have been surveyed but I believe it is a significant fraction of that number. Which implies expansion.

...

I can answer that. We have over one million galaxies that we have spectra for and all but a handful, literally,are receding from us. There is also almost another million quarts we have data for. We are not basing this off of a few dozen data ponds.that is how it was discovered but since then that data just reinforces the theory.

[WayneFrancis]

If you don't believe red shift data shows the universe is expanding how can you use the red shift data to judge distances. If you can't judge distances with red shift data then you can NOT believe the universe is full of filaments and voids. The 3D structure of the universe is constructed from spectra. If the spectra is suspect then you can't believe the 3D structure.

It isn't just red shift data that indicates recession. Because if was just that "tired light" models would have more credibility. Distance measurements are verified by other means that are independent of red-shift. Type 1A super nova light curves also support cosmic expansion. Back in 2008 Filippenko had almost 600 Type 1A super nova. These supported their parent galaxies recession rates. This rules out "tired light" ideas. So then you have to say. Why are all these object receding away from us? And how are they going as fast as they are? We aren't talking the 50-600km/s proper motion you get with galaxies. We are talking about thousands of km/s with one that I just stumbled upon, SN 2008cb, that is receding at a rate of 49,571km/s.

You can't cherry pick in science. If you throw out the idea that most of the red shift we are measuring is caused by cosmic expansion then you have to ask why the super nova light curves support the interpretation that cosmic expansion is happening at the same rate as red shifts despite being a separate mechanism. If you don't believe either of these then you have to call in to question SR if you think the galaxies are moving. Ask your self why GPS works if SR was so wrong. If SR is wrong doesn't this call into question GR? You have to explain now why we are in a special location in space to see what we do, remember that with cosmic expansion you'd see roughly the same thing no matter where you where. And you'd still have to come up with an idea to replace it that is, at least, just as accurate in its predictions.

It has been said before. Expansion is the best answer because it fits the best with the observed data. The data coming from multiple lines of evidence and interpreted by different scientist all over the world.

[antoniseb]

...If you don't believe either of these then you have to call in to question ...

This whole sequence is a very nice elaboration of a point I often try (less well so far) to make when faced with similar arguments. So thanks WayneFrancis for enriching the tools I have to explain this.

[Strange]

Ask your self why GPS works if SR was so wrong. If SR is wrong doesn't this call into question GR?

Just to be picky, a GPS receiver has to make general-relativistic corrections as well (difference in gravity on the ground and at the satellite, and the satellites acceleration). So it is a direct confirmation of GR.

[WayneFrancis]

Just to be picky, a GPS receiver has to make general-relativistic corrections as well (difference in gravity on the ground and at the satellite, and the satellites acceleration). So it is a direct confirmation of GR.

Correct. I'll point out to any lurkers that he aren't worried about some big house of cards falling down here and that physics is so shaky that if you disprove expansion all of physics will fall. It is quite the opposite. We aren't talking about a house of cards about to fall. We are talking about a pyramid...very solid pyramid. And it is like someone saying "Oh the pyramids don't have that shiny lime stone finish they used too...They'll probably fall down any day now".

I guess it is pretty basic. Good theories are supported by multiple lines of independent evidence. The chance that we are completely wrong about a theory and that all those lines of evidence just happen to converge and agree so well is ... well unlikely. Its like saying Quantum mechanics is wrong and not realising that if QM is wrong that there is no reason your computer should work.

I'm wondering has anyone else noticed we've had a rash of "expansion isn't real" posts in the last week?

[rambo07]

do you think that space time is stretching ? in between the reach of gravity that a galaxy can pull towards another galaxy ,instead its own weight is pulling at space time? .....because its stretching time it will go faster than light??? but only within the gap .... ( just wondering ,,,, before the big bang ,,,, space time must have been very dense and guppy,,, when the event happened ,,, speed of light was exceeded because time was stretched ,,,,and the density of space time at present is ,,,as it is because of the blast ,,, but space time is not even and the bubble isnt round ,,, because it all depends on the pull of what galaxy at present ,,,,, but may have been rounder when younger....the edge of the universe is the end of time ????

[rambo07]

do you think that space time is stretching ? in between the reach of gravity that a galaxy can pull towards another galaxy ,instead its own weight is pulling at space time? .....because its stretching time it will go faster than light??? but only within the gap .... ( just wondering ,,,, before the big bang ,,,, space time must have been very dense and guppy,,, when the event happened ,,, speed of light was exceeded because time was stretched ,,,,and the density of space time at present is ,,,as it is because of the blast ,,, but space time is not even and the bubble isnt round ,,, because it all depends on the pull of what galaxy at present ,,,,, but may have been rounder when younger....the edge of the universe is the end of time ????

This post (a duplicate of the one above) was moved out of another thread where it amounted to a hijack. Please don't step into other Q&A threads with other questions (even if they seem related).

[antoniseb]

do you think that space time is stretching ?...

You have an idea you are trying to express, but I'm not getting it. What I'd suggest, for the sake of getting clarity quickly, is that you try to model it a little more tightly, and explain what you mean in the ATM section. People will ask for clarifications, and probably give you examples and reasons why it can't work or be right ... or there is a small chance you're on to something, in which case the clarification step will still happen.