Does this contradict the expansion of the universe?

[haitch]

Even if it's moving towards us it's taking longer than it should because the very space in between us is expanding.

I'm not convinced In the slightest on dark energy, I think of it like the proverbial balloon that they use to explain expansion. As the fabric holding it together and resisting the expansion gets thinner it gets weaker and is less able to resist the expansion. Well, that's how I like to think of it anyway...sister, can you tighten the straps on my jacket and call the doctor for a top up of the meds?

[LouisJB]

think of it as expansion of the fabric holding the atoms, expand the fabric is not the same as adding more atoms...

As mentioned, the number of matter particles is believed to stay the same and certainly independent of expansion.

It's weird, but you'll get your head around it once you come to terms with it

[Nigele2]

Fascinating thought provoking stuff.

My own hypothesis is that the universe is not alone.  And external influences will change the future course of events.

One universe makes no sense to me   

[LouisJB]

Fascinating thought provoking stuff.

My own hypothesis is that the universe is not alone.  And external influences will change the future course of events.

One universe makes no sense to me   

entirely possible and there are theories that embrace that sort of idea.

[Langy]

If you were to list the minimal amount of items possible that the Universe is made up of what would they be?

Is dark energy not within the dark matter?

[haitch]

I understand, well, as well as I think I am able, that matter can become energy or vice versa but it is one of t'other not both at once... I think???

[cantab]

The opposite. Matter is a kind of energy. Other forms of energy, such as light, have mass just the same as matter does.

[LouisJB]

If you were to list the minimal amount of items possible that the Universe is made up of what would they be?

Is dark energy not within the dark matter?

dark energy and dark matter are distinct

Basically there's matter, and energy.

but, it turns out there's a need for there to be much more matter than we can account for in stuff we can see, this additional matter is called dark matter.

It breaks down into baryonic dark matter (i.e. matter that is of the same type as we're familiar just that we can't see it, including MACHOs) and non-baryonic dark matter, which could be anything really, ideas include WIMPs etc

In terms of energy, we have all the radiation we can account for, then the need for some extra repulsive energy  - this is to account for more recent findings that the expansion of the Universe is accelerating and is akin (but not necessarily the same as) the Cosmological constant and is called dark energy.

One idea is it's energy from fluctuations in the vacuum as can be attributed to the Heisenberg uncertainty principle, but this alone is not enough. If it's real, what it really is no one really knows yet.

So dark energy and dark matter are a big mystery and might all be wrong and made up because we actually got the basic laws of physics and particularly gravity etc all wrong.

[LouisJB]

The opposite. Matter is a kind of energy. Other forms of energy, such as light, have mass just the same as matter does.

well, energy and matter are distinct, but you can convert one to the other, i.e. Einstein's famous mass-energy equivalence. This conversion of mass to energy is what releases huge energy in stars and reactors. Likewise it's possible for high energy bosons to produce particles with mass. A small amount of mass = lots of energy, so making mass out of energy requires a large input of energy!

[Nigele2]

The last one I know of is the multiverse theory. This is the theory that there are multiple universes, Like a bubble, each bubble would be a universe.

And as we know bubbles can merge together  - so suddenly we have a whole lot more 

Or can burst  

As mankind increaes his horizons he discovers new things but never has he discovered one of something.   On the current horizon is the universe.  Chances there is only one must be a very long odds possibility. 

As I look out the window here in southern England I see rain and clouds.  Guess thinking of such hypotheses passes the time.   Although today is the last day to get the tax return in.  Hope all UKites have already done them or that new EP may turn into a HMRC fine 

[LouisJB]

There is no infinite mass (or necessarily infinite density) predicted or required by the big bang.

The problem is the laws of physics we have to-date don't really don't really work at the energy levels expected in the first tiny fraction of a second of the big bang.

Steady state and bouncing universes are different and certainly the steady state theory is very obsolete now, no recent evidence supports that and most contradicts it, it's essentially been abandoned as plausible.

Most simple models are solutions to the FRW models - suggest having a look. 

Then in higher dimensions you have attempted unification with things like M-theory which may call for folded higher dimensions and the creation of a universe is possibly then explained by the collision of higher dimensional 'branes'...

None of this stuff is exactly concrete. Really the most obvious initial problem is to have a unified theory that can make gravity, QM and electro-weak unification compatible.

Since they are not, it's like at least one is wrong, more likely they all are.

However that doesn't open the floodgates to all science is wrong, it means our most accurate models and flawed (but still our best interpretation for now) and will be superseded with something more refined in the future, as more evidence and exception cases are discovered and combined into an all encompassing model.

[Rob63]

It's really unfortunate that the terms used are similar, Dark Energy and Dark Matter sound as if they are related.

In reality the "Dark" just means we havent been able to see it.

Dark energy is thought to be a property of space itself and it has a repulsive quality (rather than an atttractive one like gravity).

Therefore as space expands dark energy increases meaning there is more repulsing force = expansion of space speeds up.

Alex Filippenko does a fine job of explaining these complex theories in the Introduction to Astronomy dvd series.

[LouisJB]

just to clarify, the current theory of dark energy is that it is a constant property of space, not an increasing one.

so the amount per m^3 today is the same as it was 1s after the Big Bang or in another 10billion years. That constant is why it's similar to the cosmological constant. The important thing here is it's not affected at all by the expansion of space, unlike matter (dark or otherwise).

If you have a decreasing force due to gravity from an expanding universe (reducing in density, matter wise) and a constant repulsive force built-in to space, space first expands, possibly at a reducing rate but then turns a corner and starts to accelerate apart.

Again these are all part of and possible solutions to FRW, the key terms are k (curvature of space), R(t) the scale factor function, G, c, ΩΛ (contribution from all energy, ΩΛ = ρΛ/ρcrit _), Ω_M (contribution from matter, Ω_m = ρm/ρcrit) and most importantly all best observational evidence to-date favours; 

Ωm + ΩΛ = 1 and k = 0 (flat space)

anyway, a fair interpretation of dark "something" in current  physics is that it's a placeholder for 'some unknown and not-yet-understood [removed word] is thought to happen here'.

Hope this all helps and answers the OPs original Q

[Tonys]

It sometimes seems to me that the observed fact that the galaxies are all moving away from us is not in itself inconsistent with the earth being at the centre of it all. Obviously we can't travel to other galaxies far far away to prove it isn't so, but I wonder if there is any other purely observational evidence for the balloon model of expansion.

[Nigele2]

It sometimes seems to me that the observed fact that the galaxies are all moving away from us is not in itself inconsistent with the earth being at the centre of it all. Obviously we can't travel to other galaxies far far away to prove it isn't so, but I wonder if there is any other purely observational evidence for the balloon model of expansion.

Not sure I understand this.  The earth clearly is the centre of nothing obvious.  It circles the sun.  And as I understand it the sun (with it's children) circles a black hole in the middle of our Galaxy.    If even the black hole was the centre I see no evidense that everything is moving away from it.    Surely we will one day collide with a bigger galaxy so we must be moving towards it or it towards us.

Clearly the universe expanding, or perhaps better thought of as stretching, does not mean all things are continuously moving apart?

But great discussion guys 

[jnb]

It sometimes seems to me that the observed fact that the galaxies are all moving away from us is not in itself inconsistent with the earth being at the centre of it all. Obviously we can't travel to other galaxies far far away to prove it isn't so, but I wonder if there is any other purely observational evidence for the balloon model of expansion.

How it would it look from any other galaxy? Exactly the same, obviously they can't all be the centre of the universe and it's quite unlikely that we would special in being the centre.

[LouisJB]

yes there's no reason to think we're the centre of anything so no reason to look for explanations for that to be the case. Given we're not in the centre of the solar system, let alone the galaxy, let along the local group, let alone the cluster, let alone the supercluster... it's very unlikely we're really central to anything!

you could say we're the centre of the observable universe, but that would be true no matter where you were, you're always going to see a universe where it might appear you're in the middle, things appear to be moving away from you and the cosmic microwave background is pretty uniform across the sky.

[Davey-T]

yes there's no reason to think we're the centre of anything so no reason to look for explanations for that to be the case. Given we're not in the centre of the solar system, let alone the galaxy, let along the local group, let alone the cluster, let alone the supercluster... it's very unlikely we're really central to anything!

Be carefull with that heretical talk, look what happened to  Galileo

Dave

[Tonys]

I'm not a Ptolemaist, honest! I put it down to reading "The Goldilocks Enigma". I think where I am coming from is that as I understand it the observational evidence for an expanding universe comes from the red shifts of distant galaxies and for us it appears that these distant galaxies (not the local ones, where other interactions prevail) are moving away from us at speeds proportional to their distance and crucially that this is the same in all directions. I just wonder if there is any different kind of observational evidence available to us to show that if I was observing from a distant galaxy I would see the same thing, rather than observing differences in the distance vs red shift relationship according to the direction, which would be contrary to the balloon model. One other thought is that if the expanding universe theory is right, then presumably every little thing in it is moving apart, but it's just so small as to be totally swamped by all the other interactions of physics eg gravity. If we were to set aside all these interactions, (the ones that account for observable local movements like those of our solar system, does it remain possible (although granted highly improbable), that all the expansion started here.

[Nigele2]

Interesting but I think not based on all current logical thinking.  If we are sticking to the physical laws then the expansion is driven by something.  And if we are in the middle of it would we not see evidense of it - whatever it may be?  Equally I guess the universe could be being pulled apart by some external suction?    But why would it be important that we were in the middle of it?  And if th3 middle had importance would the sun not have to circle us?

I believe in 50 years time, and yet another 50, and so on, our understanding will increase.  And we will find nothing mystical ocurring (just as we haven't in the past:  e.g UFOs, ghosts, Loch Ness monster).   And I believe we will find ways to get to other exoplanets.  One thought would be a ship with frozen life that could be reawoken.  The ship would take possibly millions of years and maybe explore several planet bearing suns before it found a new home.  And then it would start the cycle all over again.  And would they think their new home was in the middle?

Could such a drive for continued life of already happened I hear you say?    Did we arrive from elsewhere?   I think not as our egos would demand we left signs of our previous existance.  Even Slartibartfast couldn't resist leaving his autograph behind  

[LouisJB]

Where is the middle of the universe anyway, I'm not sure such a thing exists. What was the central point of the big bang (speaking causally here) is now effectively everywhere in the universe. Expansion happens everywhere, the universe is already too big to traverse at the speed of light in the time it's existed and bits are receding from other bits 'faster than light' - so we can consider it infinite in size, well at least until we invent that faster than light speed drive...

[Nigele2]

When I was a lad I thought the concept of the universe being everything was stupid.  Just get to the edge and drill a hole.  Must be something the other side.

Then teachers introduced infinity.  I mean even an everlasting strip is eventually gone.  

Then I started thinking about girls and lost the plot 

Now getting old I realise many questions will never be answered.

What is beyond the universe?

Why is Accrington Stanley called Accrington Stanley?

Why do girls say no?

Just why?

But when I started out, before I met the rag, tag and bobtail group here, I never thought I'd be gazing at a faint but visible galaxy light years away in distance and time.  I was born in a time when the great Sir Patrick Moore would serously say on TV that the dark bits of Mars could be forests 

Maybe I'll stop asking questions and just enjoy that I live in a time when there are a myriad of things to see and ponder (especially in the sky).  And with that I leave you to the interesting discussion which I think like the universe has no end - well within my life time.  Enjoy 

[Tonys]

Well said!

[HumptyMoo]

Expansion happens everywhere, the universe is already too big to traverse at the speed of light in the time it's existed and bits are receding from other bits 'faster than light' - so we can consider it infinite in size, well at least until we invent that faster than light speed drive...

I love this stuff but unfortunately am not the sharpest tool in the box. Light speed is a speed limit according to our current understanding. So presuming we could get to that limit, would we not be breaking that limit as we traverse the expanding space from the aspect of the observer? We observe the limit being broken, so in essence it can be broken? I understand that this is more like light laying down extra tracks behind it rather than going faster as such, but, essentially it is going faster against the backdrop of the container space occupies. When I say container I am presuming that is an infinite body (for want of a better word) that space can expand into because if space itself were infinite (without the container) surely it would not be expanding as it would already occupy everything?

Sorry, that probably makes no sense to educated minds, please be gentle with me, yes, I am out of my depth

[IanL]

I love this stuff but unfortunately am not the sharpest tool in the box. Light speed is a speed limit according to our current understanding. So presuming we could get to that limit, would we not be breaking that limit as we traverse the expanding space from the aspect of the observer? We observe the limit being broken, so in essence it can be broken? I understand that this is more like light laying down extra tracks behind it rather than going faster as such, but, essentially it is going faster against the backdrop of the container space occupies. When I say container I am presuming that is an infinite body (for want of a better word) that space can expand into because if space itself were infinite (without the container) surely it would not be expanding as it would already occupy everything?

Sorry, that probably makes no sense to educated minds, please be gentle with me, yes, I am out of my depth

Think about it like this:  

- I draw a line with a pen on a piece of paper and it takes me 1 second to draw that line.  I next measure the length of the line and it is 10cm long.  So the speed of the pen was 10cm per second.

- I draw a line on an elastic band moving the pen at exactly the the same rate as above.  Again it takes me 1 second to draw that line.  I now stretch the elastic band, and then measure the length of the line and find it is 20cm long.

- In both cases I moved the pen at a speed of 10cm per second, but because I stretched the elastic band, and then measured the length of the line it looks like the speed of the pen was 20cm per second, but it wasn't, it was 10cm per second.

That is pretty much what is going on with light speed and the expansion of the universe.  The maths is more complicated because the elastic band was stretching as I drew the line, and continues to stretch even after I stopped drawing, but nonetheless it is a good analogy.