Does this contradict the expansion of the universe?

[JekylHyde]

Hi 

Lets say that we watch in a distant galaxy cluster, in that cluster all the galaxies move far away from us. but we see in the same cluster a galaxy that move away from us in a much lower velocity than the other galaxies. does this contradict the idea of expansion of the universe?

thanks

[Langy]

From what I've seen on various documentaries is that they seem to think that the universe is expanding at a consistent rate and that gaps between objects just multiply. However as far as I can find out there is no center of the universe. Which makes things a bit strange as you would have thought that the objects that move apart the least distance would have been nearer to where it all started, which surely should be the center. A bit like when you drop a stone in the water and the ripples go out.

With still so much to find out on / in the universe and the hunt for dark matter with its own gravitational pull, I dare say that dark matter and maybe other things still to find out all have a bearing on how quickly objects get moved within the universe.

Even after several hundreds of years observing the skies and the leaps in technology over the last few decades we haven't managed to get man much further than the moon. We are a mere spec within our own galaxy, let alone the universe. So I guess that there will be many more things to discover and even where we think we have answers for so many things, I bet the future may contradict some of our existing findings.

Looking in to the universe is like being able to see a live view of history, which is really strange as the distant objects will have changed and may not even exist if we were there now at this exact point in time, totally the opposite to our history we know of.

[Langy]

Correction!

All items are moving away from each other at the same speed not the same multiple.

Below may help.

http://math.ucr.edu/home/baez/physics/Relativity/GR/centre.html

[cantab]

No. It simply means that that galaxy has a high "peculiar velocity" - ie it's moving very fast compared to the galaxies near it. We might hypothesise that the galaxy was ejected from its cluster, similarly to how star clusters can eject members at high speed.

[IanL]

Hi 

Lets say that we watch in a distant galaxy cluster, in that cluster all the galaxies move far away from us. but we see in the same cluster a galaxy that move away from us in a much lower velocity than the other galaxies. does this contradict the idea of expansion of the universe?

thanks

"Lets say that we watch an apple tree and all the apples fall towards the ground, but we see from the same apple tree and apple that flies up in to the sky, does this contradict the theory of universal gravitation?"

Well assuming that there was no other force acting on the apple (e.g. a passing tornado), then yes of course it would do so.  But imagining something isn't the same as observing something is it?

[dph1nm]

The most likely explanation would be that the galaxy was on the opposite side of the cluster from Earth and falling towards the centre of the cluster. This will result in a lower measured velocity than that for the cluster as a whole. The other possibility is that the galaxy is actually much nearer us and nothing to do with the cluster at all.

NigelM

[jnb]

There will be a range of proper motions for the galaxies so while the space is expanding they can be moving relative to that so we could see galaxies moving faster or slower than the speed expect purely from the speed of expansion of the universe.

It would be a bit like watching people on a moving walkway in an airport. Some people will be standing still on the walkway but they still move away from us at the speed of the walkway, some might be walking along the walkway and we see them travelling faster than the speed of the walkway. If you see one person walking the wrong way and apparently being much slower or even coming towards us it wouldn't mean that the walkway wasn't moving.

[Wetsparks]

Apparently, the latest thinking is that the expansion of the universe is actualy increasing in speed, not slowing down. Prof B Cox said this the other week on sky watch 

[LouisJB]

universe is believed to be expanding at an accelerating rate, this is not a new finding though, well it's a few years old now.

peculiar velocity - is exactly the right term for motion against the general fabric of space

although we measure and interpret movement with speed, measuring the velocity of a distant galaxy (via red-shift) will combine the measurement of two properties. One is the peculiar motion, it's velocity against the backdrop of space (whatever that is) and the other isn't really velocity, it's actually a measure of the relative change in scale-factors between now and then (then being when the photons were emitted).

Also, there is no expansion in a gravitational bound system, like a star cluster, galaxy, galaxy cluster. Even more so in the tightly bound chemicals of our bodies and the Sun and planets, these forces are much stronger than the Hubble flow that is causing the general size of the universe to expand (at an accelerating rate).

[bingevader]

The short answer is that nobody really knows! That's why they're called hypotheses or theories. It's why people like Richard Dawkins give me a rye smile, they're so certain about these uncertainties! Good question though, it'd be a great sadness if we stopped asking.

Cheers

[JekylHyde]

great answers so far

if you have anything else i'll be happy to read!  thanks

[Davey-T]

Bit like the "Red Shift" in my wallet as astro spending expands faster than I can fill it with cash

Dave

[JekylHyde]

No. It simply means that that galaxy has a high "peculiar velocity" - ie it's moving very fast compared to the galaxies near it. We might hypothesise that the galaxy was ejected from its cluster, similarly to how star clusters can eject members at high speed.

if it got ejected then its speed need to be faster than of the expanding universe no? so it needs to move towards us... 

[ollypenrice]

The short answer is that nobody really knows! That's why they're called hypotheses or theories. It's why people like Richard Dawkins give me a rye smile, they're so certain about these uncertainties! Good question though, it'd be a great sadness if we stopped asking.

Cheers

As you express yourself here you seem to be using 'hypotheses' and 'theories' as if they meant the same thing. They are very different things. An hypothesis is an imagined explanation for something. (EG 'Maybe the repetitive signal coming from the Crab Nebula could be produced by the neutron star hypothesis of Fritz Zwicky in the 1930s.) Before either Zwicky's neutron star hypothesis or the later Crab Nebula hypothesis can become fused into a theory they have to pass observational tests and, ideally, make predictions. A neutron star in the heart of the Crab Nebula remained a mere hypothesis until the observational evidence in its favour became overwhelming. So a theory is established by passing observational tests. An hypothesis is just a working idea to be looked into. The phrase we often hear, 'That is just a theory,' shows no understanding of what a theory is. It is 'just a theory' that if I belt my finger with a lump hammer it will hurt. It's a good theory though. I believe it.

What are the certainties of Richard Dawkins to which you object? 

More directly relevant to the OP, Halton Arp catalogued galaxy clusters with members showing anomalous redshifts. He used this to challenge the redhift hypothesis but it now seems that what looked like clusters weren't really clusters. Good on him for doubting though. Doubt lies at the heart of science.

Cheers to a rye smile! 

Olly

[John]

I think we need to keep the discussion on astronomy rather than embarking onto some of the topics that Richard Dawkins is known for folks. 

Thanks 

[ollypenrice]

I think we need to keep the discussion on astronomy rather than embarking onto some of the topics that Richard Dawkins is known for folks. 

Thanks 

He is principally a geneticist, John. But I take your point.   

Olly

[John]

He is principally a geneticist, John. But I take your point.   

Olly

Yes, I know that Olly

[LouisJB]

it's not wise to disregard our best interpretations of observational and theoretical science. Unless you know at least as much as the experts, then you have a chance to speak about alternatives.

Most 'wrong' science is replaced with something more refined, that encompasses and enhances it - not completely overturns it. e.g. primary example is relativity enhancing Newton's theories.

Saying we know know nothing is more of a philosophical debate. We've accumulated a lot of information that constrains possible explanations, there's still a lot we don't know but you can't use that as a basis to throw out everything we do know so far...

[LeeWilky]

Dont forget that in galaxy clusters larger galaxies also pull smaller ones towards them.  For example we will one day be part of Andromeda as we are slowly being pulled into it.

[Langy]

Another question relating to the expansion of the Universe where I'm probably going to be over my head on the first line and will be shot down in flames 

Everything is made up of Atoms, now I haven't seen any reference that Atoms multiply but are there making everything up.

So as the universe is expanding where is all this extra bits coming from?

The only thing I can tell is that it's the dark matter for which we have not been able to see or know what it is made of which is expanding and moving all the objects.

[LouisJB]

hi, no new particles like atoms are created due to expansion, so everything is getting more distributed, but stuff already clumped will tend to stay together. So we end up with something like a growing sponge with ever bigger voids between the clusters of galaxies. If that makes sense?

It's believed during an earlier period of the universe mostly all matter annihilated when anti-mater met matter and was destroyed, producing energy, the remainder, about 1x10^-9 is all matter we know today and that number has essentially not changed since and is independent of the expansion of the universe.

There is one thing thought to be filling it, dark energy, which in some interpretation is energy from the vacuum, but here we get to the fringe of what is known by the support of evidence vs. what is a guess. Dark energy and dark matter are two placeholder names for basically lots of stuff we think may exist but don't yet know what it is (at all).

[jnb]

Not shot down in flames at all, no question is silly apart from the unasked ones.

Atoms make up only a small part of what is in the universe. If I recall correctly it is about 5% matter, 20% dark matter, 75% dark energy, though that's from memory so I could be wrong on those numbers. But that is what is in the universe, not what the universe is made of. The universe is the space in which that stuff is found and it is that space which is expanding not the stuff itself. An analogy would be that it is more like a cloud of smoke expanding from an explosion, the smoke expands but just gets more diffuse as it expands. It's not like a petri dish of mould where the mould expands because it grows in a petri dish of a fixed size.

[Langy]

So where are the new particles being created? Is it just a case that where something is being moved away from the empty space is then filled with new particles?

If it's dark energy then no one really knows what it is other than it is there and has mass as it is causing gravity which keeps the various galaxies in their shapes. If it's dark matter we can't see it or know what it is made of so then there would be no new particles there.

[IanL]

Everything is made up of Atoms, now I haven't seen any reference that Atoms multiply but are there making everything up.

So as the universe is expanding where is all this extra bits coming from?

The only thing I can tell is that it's the dark matter for which we have not been able to see or know what it is made of which is expanding and moving all the objects.

The atoms aren't multiplying, the space between them is expanding (on the large scale at least).  Gravity holds the nearby atoms together, and by 'nearby' we mean everything up to the scale of super-clusters of galaxies.  So in essence we have the same amount of 'stuff' in a universe that is getting bigger and bigger.

Dark matter is actually the majority of what is holding things together on the scale of galaxies and galaxy clusters/super-clusters.  There is more gravity than can be explained by what we can actually see (the stars, gas and dust that we observe with telescopes).  Whatever is creating this extra gravity is 'dark matter', but nobody actually knows what it is.  If there was no dark matter, then galaxies would actually fly apart as the stars, gas and dust in them is moving too fast to be held together by its own gravity.  (More correctly, without dark matter the galaxies would not have been able to form and we'd just have a universe full of gas whizzing about in a big formless cloud).

What is driving the expansion of the universe is something else, called dark energy.  If the universe contained only normal matter and dark matter, it would either:

- Have too little gravity and would continue to expand at a steady rate forever; eventually we'd be in a little(ish) island of galaxies and would not be able to observe the rest of the universe.

- Have too much gravity, which would slow the expansion down over time, and eventually cause the universe to start contracting again and we'd all end up meeting in the opposite of the big bang, i.e. the big crunch.

In fact what has been observed is that the expansion of the universe is accelerating.  For that to happen something must be driving it, which has been called dark energy.  Currently it is believed that the majority of the stuff in the universe is this dark energy, and we have even less idea what it is than we do about dark matter.

[jnb]

So where are the new particles being created? Is it just a case that where something is being moved away from the empty space is then filled with new particles?

If it's dark energy then no one really knows what it is other than it is there and has mass as it is causing gravity which keeps the various galaxies in their shapes. If it's dark matter we can't see it or know what it is made of so then there would be no new particles there.

There are no new particles being created in the empty space (*) the existing particles simply become more diffuse. This is more obvious when you consider the early universe before matter started to coalesce under gravity's influence.

* - though interesting that is what Hoyle proposed to try to reconcile the expanding with his ideas of a steady state universe, but that creates an unstable solution