dark energy ?

usemyillusion12

ok , i know there isn't much known about dark energy relating to the expansion of the universe but does anybody know anything about it ?

does it just exist between the galaxies ? as it seems to be as if it were uniform in the universe, we would all expand at the same rate and we couldnt detect it , and if this is the case , why is it only between galaxies?

if you were to travel into some , would you expand also ?

and also because it is causing the expansion of the universe to accelerate , then it must be constantly feeding energy into the universe to cause it to be accelerating , and would this mean that the total energy in the universe is not a constant but is increasing ? and perhaps the universe is not an isolated system ?

sorry if i didnt explain my points very well but thats the best way i could put it , im sure there must be some answers , ive looked around but couldnt find any answers

thanks

Kevster

Hi,

Dark Energy is a largely unknown area of cosmology. Well, it's known, but do we really know what it is? At the moment, it's just the energy that results from Einstein's relativity theories (the so-called 'Cosmological Constant'). It's not actually anything detectable and I don't think anyone has postulatd what type of particle it could be. Dark Matter - on the other hand - has been indirectly detected.

Your question are vague, but the one about us expanding is interesting! However - no - we wouldn't expand. We are single entities and our molecular structure is held tightly together. It is the 'fabric' of space that is being strectched. Everything else is 'self-contained', in a way. Think of it like this: You have two balls and the gap between them is space. That space is expanding (ie - the balls drift further apart), but the balls remain the same size.

Kevin

usemyillusion12

yes , but if the spacebetween our molecules is getting bigger , would we not get bigger overall ?

but the thing i am still wondering about is the way it is energy , where is this energy coming from ? , i was always told the mass-energy in the universe was constant , but it doesnt seem to be with this , and also , if extra energy is being fed into our universe , does that not mean that our universe is not an isolated system , and must be in contact with some other system also

Kevster

Hang on a second dude. We are 'self-contained' entities. Our molecules are neatly packed together and aren't affected by the Universe's expansion. Everything in the Universe isn't expanding - What's expanding is the gaps between them. People always think of a balloon inflating to highlight this expansion.

Why does it not 'seem' to you that the Universe's energy is constant? Energy is constantly being recycled here, there, and everywhere, and it's never 'just' created.

Kevin

usemyillusion12

yes , but there is always a gap between everything , no matter how small , due to the electromagnetic force ( the electrons in your hand repelling the ones on your keyboard and vice versa ) , thus you never touch anything , so there is always a small gap , and why does expansion not occur in this small gap ?

and energy is being constantly recycled , but this energy must be massive to be accelerating the galaxies away from each other , where could this energy be coming from ? , i know energy gets recycled , but this is a huge amount of energy , where could this possibly come from ?

Kevster

usemyillusion12 wrote: »

yes , but there is always a gap between everything , no matter how small , due to the electromagnetic force ( the electrons in your hand repelling the ones on your keyboard and vice versa ) , thus you never touch anything , so there is always a small gap , and why does expansion not occur in this small gap ?

and energy is being constantly recycled , but this energy must be massive to be accelerating the galaxies away from each other , where could this energy be coming from ? , i know energy gets recycled , but this is a huge amount of energy , where could this possibly come from ?

haha, I know that there's a gap between everything - I'm not dumb. However, you are forgetting that all of our molecules - and all of the molecules on Earth - are held together by the four fundamental forces: EM force; strong nuclear force; weak nuclear force; and gravity. So, the expansion of the Universe isn't strong enough to be tearing us apart, or our planet for that matter. Our solar system isn't getting bigger or smaller either, because the gravity of the Sun keeps everything together; just as the dense core of the Milky WAy keeps the entire milky way together.

There's no masssive amount of energy needed to be accelerating the gravities away from each other. If you go up into space and hit something in one direction, it will never stop moving until it collides with something. After the 'big bang', everything was set in motion to be moving away from each other, and this is what we observe today.

usemyillusion12

but thats not what we are observing , the universe is not moving away with constant motion , it is accelerating , and thus a force must be constantly acting on it which requires energy

i see what you mean about the other point now , i just couldnt see that , thanks

skinner2x

usemyillusion12 wrote: »

but thats not what we are observing , the universe is not moving away with constant motion , it is accelerating , and thus a force must be constantly acting on it which requires energy

i see what you mean about the other point now , i just couldnt see that , thanks

Yes , but is the rate of acceleration increasing or decreasing? (I can't remember, saw it somewhere in a documentary.). Its like a bullet being fired, its still accelerating for a while from the initial explosion .the big question is will gravity be able to haul the universe back in (the big crunch), or will the expansion keep increasing (the big freeze..).
I'm inclined to lean towards the big crunch theory, but that would be off topic.......

usemyillusion12

i think the acceleration is actualy increasing ,if i remember correctly , and i think the universe is actually heading for a big freeze also

Kevster

I think that it is accelerating too, actually, but I can explain it somewhat: If inflation occured, then perhaps this is what is still causing the acceleration. Inflation is the faster-than-light expansion of the Universe which happened moments after the Big Bang. Who's to say that inflation ever stopped? It has slowed down somewhat though, obviously. That's just a theory that isn't based on any solid facts though.

Is there any reason why you think there'll be a 'big freeze'?; and what's your interpretation of this 'big freeze'? I believe that the Universe is going through perpetual cycles of expansion and contraction. We are in an expansion phase right now, but it will begin to contract once more and then there will be another 'big bang' moment.

...what's going to cause everything to contract is beyond me though.

usemyillusion12

the universe will go into the big freeze , this is when the galaxies will be isolated from each other due to them travelling away fromeach other , the night sky will then have no other galaxies in it , and eventually the suns will burn out due to the hydrogen burning out , then there will be no light , no heat , thus a big freeze ,

there are 3 possible scenarios ,
1) the universe expands , then under the influence of gravity it collapses back onto itself ,
2) the universe expands just the right amount to counter gravity and then remains in a fixed equilibrium state of motion
3) the universe expansion is so great it overcomes gravity and continues expanding forever , due to observational data and math based solutions , the 3rd option is the most likely , i do have more info on it , but i gave most of my books away to a friend , i do believe it was an eastern european who discovered this , i think it was during world war 1 or 2 , but i wouldnt quote me on that !

Kevster

I knew the three scenarios that have been postulated, but I just wanted to hear what your interpretation of the 'big freeze' was. If it does go into this big freeze though, don't you think there is an opportunity for everything to slowly draaaaaag itself back together again? This might not happen for many trillions of years from now when all of the remnant black holes have evaporated into 'nothingness', but I think it's still feasible for everything to recollapse in the big freeze

Podge_irl

Kevster wrote: »

I knew the three scenarios that have been postulated, but I just wanted to hear what your interpretation of the 'big freeze' was. If it does go into this big freeze though, don't you think there is an opportunity for everything to slowly draaaaaag itself back together again? This might not happen for many trillions of years from now when all of the remnant black holes have evaporated into 'nothingness', but I think it's still feasible for everything to recollapse in the big freeze

By the definition of what is commonly called the Big Freeze the universe won't collapse back in on itself.

Hang on a second dude. We are 'self-contained' entities. Our molecules are neatly packed together and aren't affected by the Universe's expansion. Everything in the Universe isn't expanding - What's expanding is the gaps between them. People always think of a balloon inflating to highlight this expansion.

Our molecules are affected by the universe's expansion as much as the space between them is. Spacetime itself is expanding, it cares little whether there are particles there while it is doing so (at least on a large scale). Anything that is not truly a point particle will be stretched by the expansion of space.

bonkey

usemyillusion12 wrote: »

i think the acceleration is actualy increasing

I'm not sure...

Isn't redshift an indication that the further away things are from us, the faster they are moving away from us? Given that the further away we are looking, the further back in tie we are seeing (if something is X light years away, we are seeing it as it was X years ago), doesn't this suggest that the acceleration is slowing?

usemyillusion12

if everything is being strectched the same amount , then it would be impossible for us to know that there is indeed a stretch at all , as we would all stretch at the same rate

redshift doesnt indicate how far away things are , they tell you how fast they are travelling away from you. To get the distance of other galaxies , you have to use standard candles and it isnt very accurate.

The big freeze will mean that the universe will go cold and it wont collapse back onto itself. The suns will die out , there will be no sources of light or heat , and the overall temperature of the universe will drop to just above zero Kelvin

Podge_irl

usemyillusion12 wrote: »

if everything is being strectched the same amount , then it would be impossible for us to know that there is indeed a stretch at all , as we would all stretch at the same rate

We can detect the redshift of the light from the other galaxies expanding away from us. Also, the further away a galaxy is from us the faster its being stretched away from us, so the redshift is greater.

Isn't redshift an indication that the further away things are from us, the faster they are moving away from us? Given that the further away we are looking, the further back in tie we are seeing (if something is X light years away, we are seeing it as it was X years ago), doesn't this suggest that the acceleration is slowing?

No, though its an understandable confusion. You have to realise that the universe is not expanding away from a single point, there is no centre of the universe. If you are at any point in the universe then the expansion away from you will be greater the further away from that point you are - its just a property of the way the universe is expanding. If you stretch a sheet (or indeed blow up a balloon to give the usual analogy), then points that are closely spaced will stay close-ish, but points that are well separated will become a lot more separated.

I think the acceleration is in fact increasing, which is one of the sources of confusion at the moment.

Kevster

I still don't buy the notion that the Universe will just end with a 'big freeze'. I mean, my mind doesn't want to believe it to be true. I'm sure that - given how 'loose' cosmology is - I could probably develop a theory which would indicate that the Universe would in fact recollapse upon itself. That's the nature of the cosmology 'game': Much of our theories are just that - i.e. theories - and have not been proven. That's why people woth crazy ideas can put some math together and come up with things like multiple dimensions, worm-holes, etc.

Tell you what: We'll see how it turns out and then, if I'm wrong, I'll buy you each a drink. There can't be much longer to go, can there... ...?


Kevin

Kevster

Podge_irl wrote: »

Our molecules are affected by the universe's expansion as much as the space between them is. Spacetime itself is expanding, it cares little whether there are particles there while it is doing so (at least on a large scale). Anything that is not truly a point particle will be stretched by the expansion of space.

Please be honest with me, Podge_irl: Where did you read about this before? I'm not attacking you here - just genuinely curious.

Podge_irl

Kevster wrote: »

I still don't buy the notion that the Universe will just end with a 'big freeze'. I mean, my mind doesn't want to believe it to be true. I'm sure that - given how 'loose' cosmology is - I could probably develop a theory which would indicate that the Universe would in fact recollapse upon itself.

There is a theory that the universe collapses in on itself. More precisely there is a generally accepted theory at the moment that depends on several parameters (such as the energy density of "dark energy" and dark matter). The value of these parameters is what decides whether the universe collapses in on itself or expands forever. We currently don't have particularly accurate experimental figures for these parameters, but what values we do have tends to indicate that we will indeed enter a big freeze.

Kevster wrote: »

Much of our theories are just that - i.e. theories - and have not been proven. That's why people woth crazy ideas can put some math together and come up with things like multiple dimensions, worm-holes, etc.

There is a difference between an accepted scientific theory and wild speculation. And there is far far more to it then just putting some maths together. There are actually quite compelling reaons why there should be more than our 4 spacetime dimensions.

Please be honest with me, Podge_irl: Where did you read about this before? I'm not attacking you here - just genuinely curious.

I didn't read about it, I'm just extrapolating from my knowledge of physics.

Kevster

Podge_irl wrote: »

I didn't read about it, I'm just extrapolating from my knowledge of physics.

Well, based on my own knowledge, I disagree with you on this issue. In my own take on things, space-time isn't really expanding. The objects in the Universe are simply drifting further and further apart because that is how they were set in motion in the beginning. Space-time isn't inherently expanding and, thus, our molecules would remain neatly packed together 'forever' (ignoring things like atomic decay).

Kevin

Podge_irl

Kevster wrote: »

Well, based on my own knowledge, I disagree with you on this issue. In my own take on things, space-time isn't really expanding. The objects in the Universe are simply drifting further and further apart because that is how they were set in motion in the beginning. Space-time isn't inherently expanding and, thus, our molecules would remain neatly packed together 'forever' (ignoring things like atomic decay).

Well, I'm afraid all current indications are that you are wrong. Spacetime itself is expanding, and in fact measurably so. Short of the Earth being literally the centre of the universe (and we have no reason to think it is) all measurements imply that it is spacetime itself which is expanding and that is what all our current theories are based on.

Kevster

Podge_irl wrote: »

Well, I'm afraid all current indications are that you are wrong. Spacetime itself is expanding, and in fact measurably so. Short of the Earth being literally the centre of the universe (and we have no reason to think it is) all measurements imply that it is spacetime itself which is expanding and that is what all our current theories are based on.

:pac:... ...It is rigid - conforming - thinking like yours that is not needed for the progression of cosmology. Don't believe everything you read about dude. There is a lot of incompetence out there, even by people who have a 'Dr.' in their name. Look throughout history and you will see that the biggest advances have been made by non-rigid, open, and - sometimes - aloof thinking about life and everything in it.

Kevin

Podge_irl

Kevster wrote: »

Don't believe everything you read about dude.

I don't, though I do tend to believe experimental observations. There is a difference between being open-minded and ignoring experimental evidence.

thinking like yours that is not needed for the progression of cosmology

That's okay, I'm a particle physicist, not a cosmologist.

Hoovers

Hey Kevin,

Just wondering what your qualifications are?

Kevster

Sorry Podge dude, I was just in a bad mood last night. Hoovers, you are quite nosy but I will give you my qualifications: BSc [honours] Computer Science, Higher Cert Biology, BSc Biosciences, BSc [honours] Industrial Biology. I will be starting a PhD in IR spectroscopy and ElectroSpray Ionisation soon (but I'm also in consideration for a PhD in Astrophysics in England).

I don't need qualifications to have my own opinion on how everything in life and the Universe works though. Where there is uncertainty as to how things work, there is a chance to dream and an attempt to prove (such as things in the Universe are, currently).

I don't want this to develop into a bickering back and forth like most things on Boards.ie

Take care dudes and sorry again Podge!

Kevin

usemyillusion12

all good points , but it still doesnt explain why dark energy is only found between galaxies ,

if it were found around us , we would expand at the same rate as the galaxies and thus not notice the expansion , kinda like measuring the height of a person expanding using a stick which is also expanding , you simply would not know they were getting bigger

so that means that expansion is just between galaxies doesnt it ?

Podge_irl

usemyillusion12 wrote: »

all good points , but it still doesnt explain why dark energy is only found between galaxies ,

if it were found around us , we would expand at the same rate as the galaxies and thus not notice the expansion , kinda like measuring the height of a person expanding using a stick which is also expanding , you simply would not know they were getting bigger

Dark energy is everywhere, not just between galaxies. Its true that if we are all expanding at the same rate that it makes measurements of the expansion more difficult, but the key point is that with uniform expansion objects further away from us expand away at a quicker rate. Again with the balloon analogy, two points close together stay reasonably close together as you blow it up, but two points far apart become much further apart as its blown up. The redshift we see from galaxies does imply that those further away are expanding away at a greater rate.

Take care dudes and sorry again Podge!

No worries, it gave me something to do to avoid studying anyway!

usemyillusion12

Podge_irl wrote: »

No worries, it gave me something to do to avoid studying anyway!

i know how you feel , which brings me to another unsolved mystery i could never figure out , i am studying applied phyics in dcu , so why in gods name do i have to study programing ? what the hell has that got to do with physics if i wanted to do computers , i would have chose computer science

Podge_irl

Unfortunately next to nothing in physics can actually be solved analytically. Computational approaches are quite necessary so pragramming can come in quite handy.

usemyillusion12

and when it comes to writting a programe for it , id go to a guy who knows how to , i wouldnt trust my basic knowledge of it , so in reality , it is totaly pointless

Kevster

Indeed, the PhD in Astrophysics that I applied for is actually mainly going to involve programming. They have a huge set of IR data from analysing comets, and they need a programmer (hopefully me!) to join their team. I feel out of my depth now by the way. I know that you guys are more qualified in this area than me... I'm a mere biologist! We are typically scruffy people with long beards and brown suits that haven't been washed for decades.

Anyway, take care.
Kevin