Question regarding universe expansion.

dublin_daveyboy

I know edwin hubble discovered galaxies are moving away from eachother and that the universe is expanding but how come andromeda is going to collide with the milky way ina few billion years?

ive heard it being mentioned in documentaries but with no explanation,if the universe is expanding how does andromeda catch-up with the milky way or vice versa if galaxies are moving away from eachother,

my head hurts thinking about it.

AlmightyCushion

Maybe other forces cause them to move as well. Like how gravity cause the planets in our solar system to orbit the sun. If the planets were moving due to expansion as well then they could still collide with other planets or asteroids. This is just a guess though as I haven't got a clue. I'd be interested in knowing the answer though.

slade_x

With the expansion of the universe, space is actually expanding or stretching. now the more space or distance you have between the galaxies seemingly the more that expands, much like if you had a sheet of rubber you would reach a limit before you couldnt comfortable stretch it anymore, if you then used a larger sheet of rubber you could stretch that even more.

basically the more space or seperation you have between more distant galaxies the more space you have to expand. Gravity keeps a tight grip on local galaxies given their mass of which gravity also holds them together

signals from andromeda are observed as blueshifted (the frequency has a shorter interval) and so from this perceived doppler shift you can infer that it is moving towards us

dublin_daveyboy

thanks for the reply's,i still struggle to understand how two galaxies literally millions of light years apart can interact with eachother,its mind boggling,i just cant get me head round it,

anyone got stephen hawkings number?:D

namelessguy

Stupid question but in to what is the universe expanding? An expanding balloon takes up more and more space from outside it but if everything that exists exists in the universe what is it expanding in to? Is it not just becoming less dense?

AlmightyCushion

namelessguy wrote: »

Stupid question but in to what is the universe expanding? An expanding balloon takes up more and more space from outside it but if everything that exists exists in the universe what is it expanding in to? Is it not just becoming less dense?

Yes it is becoming less dense and I'm pretty sure it is expanding into nothing simply because outside of our universe there is nothing (or at least that's what we think).

dublin_daveyboy

Its not a stupid question at all,i wana know too what the universe is expanding into,maybe theres just an endless number of parallel universes that are connected in some way.its unanswerable really isn't it.head melting stuff.

slade_x

dublin_daveyboy wrote: »

.its unanswerable really isn't it.

To put it simply yes, with our current level of understanding. we dont see that space has a boundary so we cant infer either way, either it is infinite in which case the universe itself isnt expanding into anything or it isnt and their is a larger or exotic type of structure or fabric containing it or adjacent. maybe this structure influences our universe and what we understand its physical laws to be, maybe even the birth of our universe (or its owed existance) was a cause and effect of forces of a more exotic type of structure

i guess currently the only real measure of the universe or the state of things is entropy.

An interestingly enough article on the subject however can be found at the following link:

http://curious.astro.cornell.edu/question.php?number=274

Cú Giobach

dublin_daveyboy wrote: »

I know edwin hubble discovered galaxies are moving away from eachother and that the universe is expanding but how come andromeda is going to collide with the milky way ina few billion years?

ive heard it being mentioned in documentaries but with no explanation,if the universe is expanding how does andromeda catch-up with the milky way or vice versa if galaxies are moving away from eachother,

my head hurts thinking about it.

All the Galaxies in what is called "The local group" are attached gravitationally, this includes the large and small Magellanic Clouds, Andromeda (total around 30 galaxies, the Milky Way and Andromeda are the biggest).
At the local level gravity is winning out over the general expansion of space, if you try and visualise space expanding and on a large level galaxy clusters all receding from each other but for galaxies close to each other gravity causes them to interact.
Though the force of Gravity gets weaker with distance it technically never dies off completely (ie its range is infinite) so every object in the Universe feels the gravity of every other and therefore it isn't until two objects are far enough away from each other for the force of Universal expansion to "outweigh" gravity and allow them to move apart.
It seems that because the expansion is speeding up, that eventually it will overtake gravity even on a local level.

dublin_daveyboy

cheers for the help lads and link,how gravity can make two objects so far apart interact is just crazy and the universe is expanding into nothing,so what is this nothing and how did the nothingness come into being id love to know but never will.:(

Cú Giobach

dublin_daveyboy wrote: »

cheers for the help lads and link,how gravity can make two objects so far apart interact is just crazy and the universe is expanding into nothing,so what is this nothing and how did the nothingness come into being id love to know but never will.:(

If you could answer the question "What is this nothing?" then it would be something and nothing can't come into being, it just "isn't".
So if there is nothing outside this universe then even the questions above are redundant.
Though "stacks" of extra dimensional universes is easier on the brain cells.

riffmongous

What exactly do we mean when we say the universe is infinite? As in, it already is spatially infinite? Or do we mean that it will last forever and hence 'become' infinite?

I know it's related to the geometry of the universe, which I think helps make sense of it in the non-infinite case.

Calibos

As you recall, the balloon analogy is often used to explain to people how it is that everywhere feels like the centre of the universe because nearly everything else in the universe seems to be moving away from you no matter what direction you look. ie. Imagine the 3D universe is the 2D outer surface of a balloon. Draw lots of dots on the surface of the balloon. Blow it up. Every dot gets further away from every other dot not so much because the dots are moving but that the latex/space between the dots/galaxies is expanding.

However Galaxies do have real motion within the universe. Now imagine that we didn't draw dots on the balloon but placed ants on the balloon instead. The andromeda ant can walk fast enough towards the Milkyway ant that he is still closing in on us despite the space between us stretching. However, the IC46231846 ant despite the fact that he is also walking towards us as fast as he can from half way across the surface of the balloon is still getting further and further away from us. There is just so much more stretching space between him and us that is real motion towards us is swamped by the universal expansion.

Its a similar kind of idea with black holes afaik. its not that black holes pull photons of light into themselves per se, its that black holes pull the fabric of space into themselves along which the photons are travelling. The event horizon of a black hole is the point at which the black hole is pulling in the fabric of space faster than light can traverse that space.

Rubecula

As regards gravity, and I may have the actual figure wrong here, but if you double the distance you do not halve the force of gravity, you quarter it.

(for example only:

at a distance of ten miles the g is strength twelve g.

at twenty miles it is not 6 g but three g.

at forty miles it would be 0.75 g

and so on.

I just used these numbers as an example they are not actual.)

Gravity never actually vanishes, but eventually distance makes it so negligable that momentum overcomes it. The local group's gravities are strong enough to overcome momentum due to their proximity to each other. As the universe continues to expand however, the momentum of the expansion is theorised to eventually be so strong that all matter will weaken the power to attract. (Not lose, just not be strong enough to have an effect)

One idea that matter itself will eventually come apart down to sub atomic level when the universe becomes big enough.

Make of that what you will, we have no actual proof of this last bit, just theories.

user1842

We just dont know. Remember there is no such thing as a law, only theories. The biggest problem in physics is the perception of being right. This confines thoughts into a box with current theories as boundaries. Most people channeling these theories are mocked and ridiculed. Its just who we are. The Earth was once fully "proven" to be flat but now we know that the people who thought that were ignorant. The problem is, we are just as ignorant as them but are unable to realize it.

slade_x

dmclean1842 wrote: »

We just dont know. Remember there is no such thing as a law, only theories. The biggest problem in physics is the perception of being right.

I think that statement needs a little refinement. If we didnt have laws that prove our observations and experiments you wouldn't be typing on a forum via a computer while possibly looking at a flat screen monitor. Our world as it is today would not exist if not for consistent reliable proven observations or the laws of physics as we understand them to be. On our planet physics behave themselves so much so that we have such laws.

Theoretical physics is mostly just theory however, which is probably what you meant?.

user1842

It was a general statement on the evolution of knowledge and how we approach new and unique thinking.

A professor who spends their whole life working on a theory will be unopen to that the fact that their theory can be wrong,

I believe that we should embrace questioning out of the scope of what we currently believe/theorise.

We tend to try and make observation fit into current theory, we resist change, starting from fresh. Example dark energy, dark matter, convenient constructs that fit with current theory but almost impossible to prove.

I suppose I am talking more about theoretical physics and im worried that this type of thinking boarders more on the religious than the scientific. Rigidly sticking to unprovable theories and not letting anybody with a fresh perspective through to make their point.

glenbrook

dmclean1842 wrote: »

It was a general statement on the evolution of knowledge and how we approach new and unique thinking.

A professor who spends their whole life working on a theory will be unopen to that the fact that their theory can be wrong,

I believe that we should embrace questioning out of the scope of what we currently believe/theorise.

We tend to try and make observation fit into current theory, we resist change, starting from fresh. Example dark energy, dark matter, convenient constructs that fit with current theory but almost impossible to prove.

I suppose I am talking more about theoretical physics and im worried that this type of thinking boarders more on the religious than the scientific. Rigidly sticking to unprovable theories and not letting anybody with a fresh perspective through to make their point.

True there are theories now which seem utterly unproveable, untestable such as string theory, but it has been continually criticised for this very reason.

Those that stick to beautiful theories that contradict experiment tend not to prosper in as hard a science as physics. Theoretical Physics in particular is a rarified discipline which is utterly impenetrable unless you have extra-ordinary abilities in mathematics. Since Einstein, cutting edge physics has moved out of the realm of ordinary mortals like you and me. Without sufficient understanding of the math, it's not possible to meaningfully participate in a discussion. But this does not mean that it's not impractical or untestable.

Without the theories developed by Einstein, Planck and others, computers, GPS, mobile phones, CD players all would be impossible. The need for these theories arose because certain experiments showed things that did not fit with the beautiful theories of the day. Newtonian mechanics is great, works really well, except at the margins and ignores the frame of reference. Similarly present physics works very well for our purposes but we know there are margins where it breaks down. Singularities, black holes, the big bang, these are places where modern physics cannot take us.

You mention dark energy and dark matter - good examples of "things that don't fit". They are not convenient things made up to fit a theory, they are names for parts of the system that do not work, which is why they are interesting to the scientists that study them. The difficulty is testing these and other things at the margins of physics tends to require enormous resources, such as the billions needed for Large Hadron Collider.

The LHC will prove or disprove the standard model the and the scientists that run it know that it would be a far more interesting result if the Higgs Boson was not found or better yet, proven not to exist. The LHC is also designed to probe dark matter. Despite a lot of trying, dark matter has been shown to be not like ordinary matter, composed of protons and neutrons.

There are those who, like you, see dark energy/dark matter as a failing of modern physics. The problem is that no-one has found any theory that fits the evidence better. There is nothing the operators of the LHC would like better than to crack open the current consensus and open a new chapter in physics.

user1842

Well said

perch

We nearly know everything is the message that comes across to every school kid, but the truth is somewhat less reassuring.

It may be very impressive to spend billions on a project like the LHC and the very scale of the project may give it credibility with theory first and evidence sought later. Of course all scientific progress is based on the evidence to support theory.

However more often the evidence proceeds the theory, and the theory only emerges in the light of the evidence. We are very good at ignoring evidence collected in more humble ways.

I give the example of the work of your local boards prodigy calling himself "M.T.Cranium" who is active on the weather forum. He has used the very planet Earth itself as an instrument for scientific discovery. He has gathered simple readings of temperature, pressure, etc from weather stations over more than thirty years, and used his skill at statistics to extract correlations with the movements of certain planets and stars and has evidence to demonstrate non-Newtonian correlations. He is very highly regarded over there as a weatherman, but he should be even more highly rated as a scientist, and is possibly in the Nobel prize league.

You would think that the scientific community would jump on this data and either demonstrate that there is a fallacy in the argument, or take it aboard into mainstream science, and use it as a basis for the support of theories. However there is a deadly silence. It seems to me that mainstream science is more interested in fashion and respectability than in chasing the truth. A little humility would go a long way in the process of science.

dublin_daveyboy

Lots of interesting posts lads.ive actually heard a theory on a documentary that the whole universe itself could be inside a black hole,

*head explodes*

glenbrook

perch wrote: »

We nearly know everything is the message that comes across to every school kid, but the truth is somewhat less reassuring.

It may be very impressive to spend billions on a project like the LHC and the very scale of the project may give it credibility with theory first and evidence sought later. Of course all scientific progress is based on the evidence to support theory.

However more often the evidence proceeds the theory, and the theory only emerges in the light of the evidence. We are very good at ignoring evidence collected in more humble ways.

I give the example of the work of your local boards prodigy calling himself "M.T.Cranium" who is active on the weather forum. He has used the very planet Earth itself as an instrument for scientific discovery. He has gathered simple readings of temperature, pressure, etc from weather stations over more than thirty years, and used his skill at statistics to extract correlations with the movements of certain planets and stars and has evidence to demonstrate non-Newtonian correlations. He is very highly regarded over there as a weatherman, but he should be even more highly rated as a scientist, and is possibly in the Nobel prize league.

You would think that the scientific community would jump on this data and either demonstrate that there is a fallacy in the argument, or take it aboard into mainstream science, and use it as a basis for the support of theories. However there is a deadly silence. It seems to me that mainstream science is more interested in fashion and respectability than in chasing the truth. A little humility would go a long way in the process of science.

Some answers to your questions/observations:

"We nearly know everything" yes, well I agree that some schools might teach that sort of nonsense in science class, but not from my memory. The message I got was "We basically know very little compared to the vastness of space and time. However, this is what we do know and this is the experimental proof. We will never stop testing and learning new things" However schools vary - but lets not get dragged into a discussion of science teaching.

The LHC is not intended to give credibility to a theory, it is to test the theory in the most rigorous way possible. If the theory fails the test, the theory falls. I am sure many scientists will be disappointed if the Standard Model of particle physics is disproven, but many more will be delighted because it will offer up hope of a whole new chapter in physics research.

Regading humble ways etc. Western science is not based on humility, it is based on doubt and experiment. Evidence is evidence however humble its origins. E.g. 1) a amateur astronomer in Artane just discovered a new Supernova. e.g. 2) A bunch of UK primary school children just got a paper published in Biology Letters on problem solving in bees. It's on the net, it's a really clever experiment. That's a pretty humble origin.

I suggest your friend Mr Cranium submit his ideas to a peer-reviewed journal. Of course per Carl Sagan, if you have a claim which is extraordinary, you will need extraordinary evidence to get it accepted. This is how it should be, because as I say, science is founded on doubt.

glenbrook

dublin_daveyboy wrote: »

Lots of interesting posts lads.ive actually heard a theory on a documentary that the whole universe itself could be inside a black hole,

*head explodes*

The big bang theory is essentially just that - the whole universe started as a singularity, a black hole. But singularities don't actually make mathematical or physical sense. A singularity is when you try to plot a graph where you must divide one by zero.
Well there is a very interesting new idea from Roger Penrose. He starts by attacking the big fudge in the big bang theory - inflation. It has been known for a while that the measured cosmic microwave background radiation (CMB) is far too uniform to fit with the theory. Inflation fixes this by saying that at the very start of the big bang the universe jumped in size almost instantaneously, for reasons that can't be explained because current physics cannot describe the conditions of the first moments of big bang. Penrose's idea is that instead of this, the universe came from a previous incarnation. It goes like this, the universe is expanding and in fact accelerating. If every particle in the universe starts to lose mass as it accelerates eventually everything will tend toward zero mass and move closer the speed of light. At the speed of light apparent distance between particles tends towards zero, so the universe would look infinitely small which means a new big bang.

Best of all this theory can be tested, because the cosmic microwave background radiation should contain a faint memory of the previous universe. This is theorised to be faint concentric circles visible in the variations in the CMB.

The problem with this theory is that it has its own fudge. No mechanism is known for particles to lose mass in this way. On the other hand, no mechanism is known where particles can gain mass and this is a major problem in particle physics because the big bang theory requires it. The current theory is something called the Higgs mechanism but this requires a particle which has not been observed - you've guessed it - the Higgs Boson, which is what the LHC is set up to look for.

user1842

glenbrook wrote: »

It goes like this, the universe is expanding and in fact accelerating. If every particle in the universe starts to lose mass as it accelerates eventually everything will tend toward zero mass and move closer the speed of light. At the speed of light apparent distance between particles tends towards zero, so the universe would look infinitely small which means a new big bang.

That's a fascinating theory but where did the first Universe in the cycle come from? unless its a cyclical event sequence with no beginning or end.

glenbrook

dmclean1842 wrote: »

That's a fascinating theory but where did the first Universe in the cycle come from? unless its a cyclical event sequence with no beginning or end.

I think it requires that the universe is the latter, existing forever through endless cycles. Wheels within wheels...