Can you actually say the universe is expanding? I'm not too sure but I think when we say universe we mean everything that exists anywhere. So for the universe to expand there needs to be space (or something) somewhere.

But then isn't this space supposed to be part of the universe?

:confused:

As an anology, imagine the whole universe is the surface of the Earth. Take some objects and locate them at different points on the Earth's surface. Now, suppose the Earth expands. All of the objects move further apart from each other, as measured along the surface. However, no "new" surface has been created - the surface has simply stretched.

This is the kind of thing which is happening to the space in our actual universe.

I find it funny how we can say "this is what's happening" so authoritatively. Reality's so dodgy.

As an anology, imagine the whole universe is the surface of the Earth. Take some objects and locate them at different points on the Earth's surface. Now, suppose the Earth expands. All of the objects move further apart from each other, as measured along the surface. However, no "new" surface has been created - the surface has simply stretched.


If the Earth (Universe) is stretching doesn't it need space (or something) outside of it's "boundaries" and isn't whatever it is that is outside this "boundary" part of the universe too?

Someone correct me if i'm wrong. We don't know what's outside of 'space', but we do everything is moving away from each other. In billions of years there will be no more stars in our sky, well in theory.

rug:

In my analogy, the Earth's surface is supposed to represent the entire universe. The centre of the Earth, in this picture, is not part of the universe, and neither is anything which is "above" the ground. The picture is of a 2-dimensional universe. The expansion can be pictured as having that 2-D surface embedded in a 3-D space, but the 3-D space isn't part of the actual universe.

The analogy is supposed to be easier to visualise than our real universe, but you can start to imagine what the real situation is like by bumping everything up by 1 dimension. Then you can consider our 3-D universe as embedded in a 4-D (unvisualisable) space. When our universe expands, all distances in 3-D increase equally. The 3-D space stretches, but not into additional 3-D space. It only stretches into additional 4-D space, if you're using that picture, and the 4-D space is not really part of the universe.

rug:

In my analogy, the Earth's surface is supposed to represent the entire universe. The centre of the Earth, in this picture, is not part of the universe, and neither is anything which is "above" the ground. The picture is of a 2-dimensional universe. The expansion can be pictured as having that 2-D surface embedded in a 3-D space, but the 3-D space isn't part of the actual universe.

The analogy is supposed to be easier to visualise than our real universe, but you can start to imagine what the real situation is like by bumping everything up by 1 dimension. Then you can consider our 3-D universe as embedded in a 4-D (unvisualisable) space. When our universe expands, all distances in 3-D increase equally. The 3-D space stretches, but not into additional 3-D space. It only stretches into additional 4-D space, if you're using that picture, and the 4-D space is not really part of the universe.
that's exactly how it is. once you get the idea of a sphere in your head, just imagine adding another dimension. you could say the surface of the sphere is the present, inside the sphere is the past, and outside the sphere is the future. the sphere is expanding, so the surface area is getting larger (the space between objects in the universe is increasing) but then that would make the spacial universe 2 dimensions. so to make it accurate to our universe, you just add another dimension. its just really hard to visualize it because we have only ever conceived of 3 dimensions on a normal basis.

JamesR and RoyLennigan, I think I see what you mean. It's stretching in hyperspace.

Would I be correct if I deduce that the universe is actually infinite but space is stretching thus causing galaxies to move away from each other?

Yes.

Thanks for clearing that up.

Ok, wait...

If the universe is infinite, and we're just a part of an expanding 3-D type sphere of space within that infinite universe, then it's possible that there are other (perhaps even an infinite amount of!) expanding 3-D type spheres of space like our own, yes?


(I would have started a new thread with this question, but it's so dependent on this one that I decided against it...)

Yes, it's possible, allisone. However, if other such universes exist, then they can't communicate with out universe or affect it in any way, since there is no point at which the spacetimes of the two universes can connect to each other.

The Bubbles Universes theory doesn't work in my mind. What would be between the Universes? Am I correct in saying that space-time does not exist between the Universes.

Yes, as far as I understand it (basically from what I've read in this thread), space-time would not exist between multiple universes. They would coexist in the 4 dimensional space, right?

In response to the thread question-

When scientists say that "the universe is expanding" they are reffering to the big bang theory.

When the big bang occured there was an immense expolsion (obviously), and, as everyone knows when an explosion occurs, the fragments/matter are blow outwards i.e. when a frag grenade explodes.

The same happend in our solar system, and i suppose in others, the force of the big bang is still pushing the universe outwards, making the universe 'expand'. Thats what i picked up in Gcse physics anyways. :D

I invite anyone to correct me if im wrong, which admittedly is a fairly high possibility! :) :m:

Does matter displace space? Each and every particle needs room. Matter must occupy an equivalent volume of space. The introduction of matter into spacetime resulted in a less dense spacetime making room for it. Perhaps the expansion is merely matter making room for itself. Something has to give way. If there is finite matter then expansion will stop eventually, no? In the beginning it may have been very difficult to move space but over the years space gradually weakens its position allowing matter to speed up the settling in. Spacetime and matter are like oil and water.

Nobody knows but I think it important to put stuff out there that others can read, laugh at or take seriously and run with. Sometimes innocent remarks stimulate the genius of fellow human beings. Not that mine will.

If matter were to displace spacetime would that mean that time doesn't exist within matter. Can't think logically how that would work?
But I guess one can view Einsteins classic theory of relativity as matter displacing/bending spacetime directly proportional to its mass.
Am I wrong in saying so?

As an anology, imagine the whole universe is the surface of the Earth. Take some objects and locate them at different points on the Earth's surface. Now, suppose the Earth expands. All of the objects move further apart from each other, as measured along the surface. However, no "new" surface has been created - the surface has simply stretched.

This is the kind of thing which is happening to the space in our actual universe.

Sorry to dredge up an old thread, but I just have a question regarding this:

As space-time expands, do the objects on it's surface (ie, in your analogue, the objects on the earth) stretch and get bigger too? Like, if you draw a dot on a piece of rubber then stretch it, the dot too gets bigger.

As space-time expands, do the objects on it's surface (ie, in your analogue, the objects on the earth) stretch and get bigger too? Like, if you draw a dot on a piece of rubber then stretch it, the dot too gets bigger.

Yes, they do. So, as space expands, the atoms in your body try to get further apart. However, gravity is not the only force which acts on your body. Electromagnetic forces are much stronger on that scale. So, the expansion of space "tries" to pull the molecules in your body further apart, but electromagnetic forces pull them back together. The overall effect is that galaxies move apart from each other (because the electromagnetic forces between them are insignificant compared to gravity) but the atoms in your body stay close together.

Can you actually say the universe is expanding? I'm not too sure but I think when we say universe we mean everything that exists anywhere. So for the universe to expand there needs to be space (or something) somewhere.

But then isn't this space supposed to be part of the universe?

:confused:

They mean that distance scales increase over time (in the reference frame of the universe). Forget all those analogies about balloons and rubber sheets; you don't need them when you consider length contraction in different reference frames in special relativity, you shouldn't need them here.

Thanks James R.

The Bubbles Universes theory doesn't work in my mind. What would be between the Universes? Am I correct in saying that space-time does not exist between the Universes.

What's between two blood cells that travel through your vein? Do those two cells know what it is? Does time exist for those two blood cells?

Do two fish know that water is between them and all around them? Do two monkeys know that air seperates them?

So who knows what's between the universes. Maybe we'll know, maybe we'll never know. Perhaps only those above us humans know just as only those above two blood cells, above two fish, or above two monkeys, which would only be err, us (that we know of), know what's between them. ;)

I personally like theories like that as it makes things kinda relative. What's between two planets? Atoms, cells, planets, universes.. all the same. I wonder if the scale is the same too. Is the size of an atom to a cell, the same as a cell to a planet, the exact size between a planet and our universe? And is the size between a planet and our solar system, the solar system to the universe, the universe to the multiverse?

- N

There is NO EVIDENSE THAT SPACE IS DOING ANYTHING.. let alone expanding.

the only evidense is the RED SHIFT of the spectrums from distant stars..

the spectrum from our sun is... as it is....

but the spectrum of light from distant stars is... all shifted to the right.

I.e.. in the spectrum there are obsorbtion lines... black lines in the colors of the rainbow... in the stars which are distant.. the spectrum we see.. shows that the position of every line... all of them... are shifted to the red...

meaninging whatever happens to the light traveling from distant stars... it affects all photons of all frequencies....

thus... this is the source of the expansion idea... since one way to explain this occurance.. is to say space is expanding.. and as it does so, it expands all photons....
but they must travel great distances to be noticable...

as space (based on this data..) expands something like 78 miles per parsec of space...

but... again... that isnt proof that space is expanding at all... it only suggest expansion as a possibility to expain it...

the entire idea of expanding space... is an ASSUPTION.. not a fact.

and you know what happens when you assume. dont you?

-MT

you make an ass out of you and me?

exactly....
-MT

I always suspected that Einstein & Hubble were asses. Now I know for sure.

I didnt say, or mean that... but assumption is common place in humanity.
-MT

The question is: how do you explain the red-shift observations if not by the expansion of space-time? Do you really think other explanations haven't been considered by scientists?

http://img96.imageshack.us/img96/8094/time22piec4yf.th.jpg (http://img96.imageshack.us/my.php?image=time22piec4yf.jpg)

it only looks like space is expanding... but its only moving.

-MT

MT, your hypothesis fails because you state the photons from ALL stars are shifted to the red end of the spectrum. You state this red shift is due to the photons 'expanding' due to factors associated with the ether as they travel through space. The spectrum is not shifted to red from all stars, an example being Wolf 1106. The spectrum from Wolf 1106 is blue shifted, it is approaching our sun at 260 km/s. The star is 78.2 lyrs distant. There are many stars with a blue shift in their spectrums.

Another example of blue shift is seen in the spectrum of the accretion disks of black holes. There is a suspected black hole in M87. How did they arrive at this hypothesis? Because the spectrum of the disk is shifted to the blue on one side indicating material on that side of the disk is approaching us at 550 km/s. Light from the other side of the disk is red shifted, indicating material on that side of the disk is receeding from us at 550 km/s. Galactic clusters, containing thousands of galaxies, are also converging to single points because their gravitational attraction overcomes the expansion of the universe at scales up into the millions of light years. Our own Milky Way galaxy is being drawn towards the area known as the great attractor, along with thousands of other galaxies.

No, some photons are red shifted, some are blue shifted and some don't exibit any shift at all. A coordinate frame of reference known as the International Celestial Reference Frame catalogs many stars and galaxies with no Doppler Shift as a reference system so velocities, vectors of motion, and rotations of distant objects can be determined on a common format relative to our sun.

...the spectrum of the disk is shifted to the blue on one side indicating material on that side of the disk is approaching us at 550 km/s. ...I certainly am not going to argue with experimental facts, but find this strange and hope someone will explain to me where I am thinking incorrectly.

As something falls towards a gravity source, it gains kinetic energy equal to the change in its gravitational potential. Thus, it can be acquiring increased speed relative to you if the velocity vector has a component in your direction. (Let us assume the total velocity is directed towards you.)

There is a gravitational red shift, so the net color shift will be the blue Doppler shift minus the red gravitational shift. For a particle in circular orbit I seem to recall that it is bound because the depth of the "gravitational well" is twice the kinetic energy. Lets make a numerical example in units where the gravity well is -8 and the KE = 4. The velocity is related to the root of the KE, so perhaps in a suitable scale it is 2.

Now admittedly the mass falling radially inward has more than the orbital velocity, in fact, it has he "escape velocity" for its current location, but I would think that the red shift when the photon climbs out of the gravity field would always exceed the blue shift of the escape velocity.

I know there is a simple relation between the escape velocity and the gravitational potential at the point where the escape velocity is defined. However, I cannot remember it, or easily derive it now. Can any one help understand why my intuition is wrong? I.e. how & why the blue shift of a radial infall exceeds the red shift of the gravity well?

I would have to look up the exact mechanism, but here are my thoughts from logic and understanding, which may be incorrect.

If I understand you correctly, you seem to be thinking the blue shift comes from matter on the opposite side of a black hole as it is accelerated in our direction. I may not have been clear in my above post, but the accretion disk of a rotating supermassive Kerr black hole can extend for light years from the event horizon. The blue shift and red shift from the opposite sides (think left side and right side) of the disk comes from objects in orbit around the black hole. My understanding is that objects CAN have stable orbits around black holes unless there is a change in the mass of the black hole due to it 'feeding' actively. A change in mass due to feeding would increase the gravitational attraction of the black hole, leading to orbiting objects gradually being drawn towards the event horizon, or an increase in their orbital velocity to maintain stable orbit. I have read a new paper where they detected NEW stars being formed in the accretion disk! The dust and gas was able to accumulate while inside the accretion disk and form new stars, so it is now thought that the accretion disks are not as chaotic as once believed. I don't remember the link to the news, but I can probably find it if you are interested. Meanwhile, here is a link to the SWIFT satellite website that gives real-time news on the detection of gamma-ray bursts, thought to indicate the formation of new black holes and the greater energy bursts of catastropic events concerning black holes. Thet believe they have witnessed a black hole 'eating' a neutron star recorded on Nov. 11, 2005. Scan down the tables until GRB 05111A is located, then click on the line to get a description of the event in the block to the right. This site is very interesting to me.
http://grb.sonoma.edu/

yeah, your probubly right.
-MT

...This site is very interesting to me.
http://grb.sonoma.edu/Yes me too, but I am confused why the most recent entry was observed on 16 MAY 2006 - THAT IS NOT 1 APRIL 06 - WHAT IS GOING ON?

Maybe someone was celebrating New Years when they made the typo. My observation was JULY 16, 2006 for the last two entries at the site.

James,

So, as space expands, the atoms in your body try to get further apart. Isn’t this just pure speculation?

However, gravity is not the only force which acts on your body. Electromagnetic forces are much stronger on that scale. So, the expansion of space "tries" to pull the molecules in your body further apart, but electromagnetic forces pull them back together.So if expansion were to exist then its effect locally would be nullified by EMF. Doesn’t that mean that expansion doesn’t exist because if we examine any point in the universe from its local perspective expansion there would also be null due to EMF. At what point in the universe could we say that expansion is occurring because EMF does not exist?

The overall effect is that galaxies move apart from each other (because the electromagnetic forces between them are insignificant compared to gravity) but the atoms in your body stay close together. So here is where I am confused. What is the difference between expanding space and gravitation? These are different phenomenon, right? Gravity we know but expanding space is only baseless speculation, right?

Can you actually say the universe is expanding? I'm not too sure but I think when we say universe we mean everything that exists anywhere. So for the universe to expand there needs to be space (or something) somewhere.

But then isn't this space supposed to be part of the universe?

:co
nfused:

Dear Readers:
Excuse my absence over the last few months. To answer your question, I will simply say the universe respirates i.e. breaths.Depending if we are in an exhalation or inhalation period the cosmos will appear to either be increeasing or enlarging or decreasing.The universe as our planet is a living entity, all of which comes from the mind of the creater.

Sincerly: Machiaventa @ Machiavent2@yahoo.com

Mach,

The universe as our planet is a living entity, all of which comes from the mind of the creater.Oh give me break. There's a forum for religious crap. Just stick with science here please.

Originally Posted by rug
Can you actually say the universe is expanding? I'm not too sure but I think when we say universe we mean everything that exists anywhere. So for the universe to expand there needs to be space (or something) somewhere.

But then isn't this space supposed to be part of the universe?

:confused:

well according to the big bang theory from the event that caused it it is causing an outward expansion like the shockwave from a implostion or somthing of that sort it basically keeps expaning in a sphere its very hard to explain but imagin a balloon the event of you blowing air in it cause's it to expand

Cris,

So, as space expands, the atoms in your body try to get further apart.

Isn’t this just pure speculation?

It can't be directly tested, but it is consistent with everything else we know. If expansion of space happens at all, it makes much more sense that it happens everywhere - not just on "large" scales. Don't you think?

So if expansion were to exist then its effect locally would be nullified by EMF.

Only where the density of electrically charged matter is large enough.

At what point in the universe could we say that expansion is occurring because EMF does not exist?

At the point where the separation between charged particles is sufficiently large that the expansion of spacetime is a larger effect than electromagnetic attraction or local gravitational attractions. In practice, this mostly means between galaxies.

And it's not that EM forces don't exist. They just aren't strong enough. Moreover, most large-scale objects are electrically neutral, so there is no net electrical attraction between large-scale objects like human beings or planets.

What is the difference between expanding space and gravitation? These are different phenomenon, right? Gravity we know but expanding space is only baseless speculation, right?

According to Einstein, gravity is an apparent "force" which is actually a manifestation of the structure of space and time. So the expansion of space is a gravitational phenomenon, by definition. Expansion of space is about how spacetime curves on very large scales. Locally (on a human or planetary or solar system scale), this curvature is completely swamped by local curvature effects rather than global effects.

Mach,

Oh give me break. There's a forum for religious crap. Just stick with science here please.

Cris:
If the universe was not made by the creator, just who or what do you think created all that we see and exist in.I am not a religious person at all.I think science is a way of explaining what we may call God or whatever. I try to think out of the box whenever possible, do you? :cool:

If the universe was not made by the creator, just who or what do you think created all that we see and exist in.

If God created the universe, who created God?

If God created the universe, who created God?
Cecil B. DeMille?

I AM THAT I AM...

If God created the universe, who created God?It's a self assembly job. God creates the Universe, which through a series of evolutionary steps (in the broadest sense of the word) increases in complexity until it is God, who then returns through time (he is omnipotent, after all) and creates the Universe.

If God created the universe, who created God?

Probably George Burns. :D