Is the universe truly expanding?

[tressure]

If you're in space and you pull your hands apart, there doesn't have to be something coming in between. Space is just separation between things. It's nothing but "distance" (Except if you want to talk about photons, cosmic particles, virtual particles etc.)

Space is expanding at an accelerating speed, what you are saying now is: galaxies are moving apart, which isn't what physicist are speculating about.

 

[guywithdoubts]

Ii thought of somethig today ... after all the research i did online ...it makes sense to me that some matter is getting eaten by space, that is why it appears to be growing/ expanding. Then the big question would be: if this is true, which matter is it? Is it ev en possible for a matter to transform into nothing?

How could matter be eaten by space? What do you mean? Matter cannot transform into nothing as not even the nothing you think of (the absolute absence of everything else) really exists in our Universe. Particles can decay into other particles, but overall quantities in the event are conserved.

Space is expanding at an accelerating speed, what you are saying now is: galaxies are moving apart, which isn't what physicist are speculating about.

Physicists say that expansion = moving apart. Space expanding at an accelerating rate = galaxies moving apart at an accelerating rate. If the Universe consisted of two objects, then the two objects would simply "drift away" from each other. Both, at the same time, would measure the other object to be getting farther and farther away. That is all. Replace "objects" by "distant galaxies" and that's our Universe.

 

[tressure]

Okay, i assume you know about multiverse, there should be a boundary, that bounds everything in our universe. If the universe is not expanding and its contants are being spread out, don't you think they would by now have spread outside of the universe?

 

[guywithdoubts]

Okay, i assume you know about multiverse, there should be a boundary, that bounds everything in our universe. If the universe is not expanding and its contants are being spread out, don't you think they would by now have spread outside of the universe?

The idea of a multiverse is highly hypothetical. By that I mean we have absolutely no proof it is even a feasible concept. It may or may not exist. Anything you attempt to deduce from it is meaningless.
For the hundredth time: the universe is expanding because its contents are spreading out. That is what expansion means: for its contents to spread out, to get farther away, to move apart. In cosmology they are all synonymous. So yes, the Universe is expanding and its contents are spreading out. And yes, objects (galaxies) are constantly disappearing beyond the cosmological horizon, due to the accelerating rate of expansion. That does not mean they are disappearing into some strange, magical and unexplainable realm—they are simply so far away now that we cannot detect them anymore. They are still in the Universe, but not in the observable Universe. There is no need to invoke multiverses to understand this.

 

[Drakkith]

Ii thought of somethig today ... after all the research i did online ...it makes sense to me that some matter is getting eaten by space, that is why it appears to be growing/ expanding. Then the big question would be: if this is true, which matter is it? Is it ev en possible for a matter to transform into nothing?

No, it is not possible. Please stop speculating.

Okay, i assume you know about multiverse, there should be a boundary, that bounds everything in our universe. If the universe is not expanding and its contants are being spread out, don't you think they would by now have spread outside of the universe?

The details of multiverse theories are beyond the scope of mainstream science at this time. At best we have vague guesses backed up with math and theories that are highly speculative and almost certainly wrong. As such, there is no answer to your question. While the possibility exists that there is a boundary, the prevailing belief is that the universe is either infinite and without a boundary, or finite, in which case it wraps back onto itself and also has no boundary.

What we do know is that objects which are not bound together through gravity or one of the other fundamental forces of nature are moving apart over time, with the recession velocity increasing linearly as the distance between the objects grows. This is exactly what expansion is, whether it's cosmological expansion or the expansion of a rubber band as it is stretched. We also know that the rate of this expansion was slowing over time until recently, when it began to increase once more. Hence we say that the expansion is accelerating.

What happens at the 'edge' of the universe, if one exists, is unknown and any guesses would be pure speculation and against PF rules unless backed up with a proper reference.

If you want to learn what we know about the universe then feel free to ask, but if you want to make wild guesses on speculative topics then I will close this thread. I understand that it can be hard to tell when you're overstepping the boundary between mainstream and speculation, so if you have any questions about it feel free to message myself or another mentor.

 

[tressure]

Thank you i will have a look at it.

i am reading the document, and so far it is making me even more confused, because what's said there is the opposite of what everyone is saying here. they say that galaxies are static, only space between them is getting bigger. where as you guys are saying galaxies are moving apart, whose telling the truth here?

 

[tressure]

i apologise for my speculations, i guess i just got a bit carried away.

Charles H and Tamara M.Davis in Scientific America INC wrote that galaxies are static, only that space between them is getting bigger. (obtained from diogenesNY's post is this document http://astronomy.case.edu/heather/us211.07/misconceptions.pdf ) is where i obtained this information.

now who is right and who is wrong?

 

[Drakkith]

They both mean the same thing. Galaxies are not under a force that would accelerate them and be able to be measured by an accelerometer, so in that sense they are static. Yet they are indeed moving apart, so it is common to say that space is what is expanding. However, space is not a physical object. To measure the properties of space we have to observe how objects within space act. So saying that galaxies are receding from each other and saying that space expands mean the same thing in regards to what we observe. In any case, the theory itself only says one thing, its just difficult to convey what a highly mathematical-based theory says in its math in everyday language.

 

[AshUchiha]

Tressure, Space is expanding true, very true. And eventually accelerating at a high pace. Scientists still aren't much sure of the reason but they say it's due to the Dark Matter, or maybe the Dark Energy. Hope this answered you

 

[mfb]

but they say it's due to the Dark Matter

No, certainly not. Dark matter is slowing expansion in the same way regular matter does.
Dark energy is accelerating it, and in our current universe dark energy wins.

 

[AshUchiha]

Thats why I said "or maybe the Dark Energy" please read what I said before quoting

 

[mfb]

Following this logic, you would not object to the statement "scientists say the moon is made out of cheese, or maybe rock"?

 

[AshUchiha]

Okay, my fault, but cheese and rock are two completely different things. But not Dark Matter and Dark Energy aren't that much different

 

[mfb]

Dark matter and dark energy are completely different things. The only common things are one half of their English names, and that we cannot observe them in labs (yet?). Cheese and rock are much more similar.

 

[AshUchiha]

Inbox please. But I guess the 'topic starter' would have got his answer by now.

 

[Naturestan]

As an complete armature I think its misdirected to think our Universe is self contained when it is probably exposed to whatever is outside of our universe - it is interacting with our neutrinios as its anti matter collides with them, extinguishing the anti matter (as usual) and creating more Space. Neutrinos go in all directions so Space is expanding in all directions. Simple. Wish I could do the math to see if I'm right or wrong though.

 

[Drakkith]

As an complete armature I think its misdirected to think our Universe is self contained

The question of whether the universe is self-contained or whether it exists within a multiverse is not a simple one and there is no way to resolve it at this time. There may never be a way to resolve it. Since we are observing our own universe, and have zero evidence for a multiverse, I think it makes sense to take the stand of a single universe at this time. It's certainly the right thing for modern cosmology to do at this time.

it is interacting with our neutrinios as its anti matter collides with them, extinguishing the anti matter (as usual) and creating more Space.

None of this makes any sense in terms of real science. Please avoid giving personal opinions and theories, especially when you're unfamiliar with the physics involved.

Wish I could do the math to see if I'm right or wrong though.

Sorry that this is blunt, but it's not that you're wrong, its that you haven't even made a logical, coherent claim that makes any sense. We know how anti-matter and neutrinos work. We know much about the expansion of space. Neither of them work like you're imagining.

 

[tressure]

No, certainly not. Dark matter is slowing expansion in the same way regular matter does.
Dark energy is accelerating it, and in our current universe dark energy wins.

at ashuchiha and everyone:
no, that doesn't answer my quest. i need to know how can nothing grow in size, is there any matter that is getting taken out of our universe, i just struggle to making sense that how can nothing grow at an accelerating rate.

imagine vacuum in bottle for instance, for there to be more of it (vacuum) in that bottle, more air has to be sucked out. which is why i suspect that there could be some matter large in size, and somehow is disappearing.

 

[AshUchiha]

E=mc^2 I guess this could help you ? http://en.wikipedia.org/wiki/Mass–energy_equivalence . If there is a vacuum formed it means there is no air right? Then why more air needs to be sucked out? Vacuum is a space entirely devoid of matter {By wiki}. So I don't need it needs to suck out more air unless/until there is another external force acting on it which may put a hole in it letting the air inside it or any other circumstances that would lead to the pathway of Air to that bottle

 

[nitsuj]

at ashuchiha and everyone:
no, that doesn't answer my quest. i need to know how can nothing grow in size, is there any matter that is getting taken out of our universe, i just struggle to making sense that how can nothing grow at an accelerating rate.

imagine vacuum in bottle for instance, for there to be more of it (vacuum) in that bottle, more air has to be sucked out. which is why i suspect that there could be some matter large in size, and somehow is disappearing.

I didn't see anyone say it explicitly, but what is being created is more distance...that is the meaursed difference.

 

[Bandersnatch]

i need to know how can nothing grow in size

You know how distance can grow? You've got a car, or a plane or whatever moving away from you, and this thing called distance grows. Ask yourself what is distance? Is it a physical thing? Does it matter if there's air or vacuum in-between you and the receding object for the distance to grow?

Space is like distance - a measure of separation between objects - only in three dimensions. Where objects are relative to each other. It can grow or shrink in the same way distance can, but it does not imply in any way that it is a material thing.

(you were faster, nitsuj )

 

[earnric]

Space is vaccum, does this vacuum expand? Where does it come from? if we measure it to be 15 today, and tomorrow it is 20 where did the extra 5 come from?

Space(-time) is a "thing" ... it has dimensions and (from our measurements of the expansion) a negative pressure. The more space-time you have, the more negative pressure. Hence the 'expansion' of space accelerates. This is what we are measuring.

We don't yet have a good handle on the source of the negative pressure other than to say it is intristic to space time. It is what we call dark energy.

What we 'measure' is that more space-time is being created constantly.

 

[Labyrinth]

Say the universe was 1 dimensional, with a seemingly endless number of objects each perfectly separated by 1 unit of distance strung along the 'line'.

If each object moves away from the other, without getting closer to any other, does that not imply that the 1 dimensional line is expanding?

If so, it seems intuitive then to consider the 'line' to be made of some substance, a substance that is either uniformly increasing its size, or stretching without noticeable changes in the properties of the 'line', or is this a fundamentally flawed intuition?

 

[earnric]

Say the universe was 1 dimensional, with a seemingly endless number of objects each perfectly separated by 1 unit of distance strung along the 'line'.

If each object moves away from the other, without getting closer to any other, does that not imply that the 1 dimensional line is expanding?

If so, it seems intuitive then to consider the 'line' to be made of some substance, a substance that is either uniformly increasing its size, or stretching without noticeable changes in the properties of the 'line', or is this a fundamentally flawed intuition?

If you consider the "line" to be space-time itself, you have the idea.

You can easily extend this idea to 2D by considering the surface of a balloon. Blow it up a little, use a marker to create dots on the surface... Blow it up more: you will notice that every dot moves away from every other dot on the surface. There is no 2D center of expansion... More surface is "being created" (actually stretched in this case) everywhere simultaneously.

This is what's happening to space-time. At every point in the universe, more space-time is being 'created'. Only the electromagnetic forces between atoms in your body keep you from being 'stretched' apart. Just as gravity keeps the solar system together (overcoming the expansion) ... as it does for our galaxy, etc. Only on the largest cosmological scales do things 'move apart' like the dots on the surface of the balloon.

 

[earnric]

at ashuchiha and everyone:
no, that doesn't answer my quest. i need to know how can nothing grow in size, is there any matter that is getting taken out of our universe, i just struggle to making sense that how can nothing grow at an accelerating rate.

imagine vacuum in bottle for instance, for there to be more of it (vacuum) in that bottle, more air has to be sucked out. which is why i suspect that there could be some matter large in size, and somehow is disappearing.

space-time is not "nothing" ... space-time is a stage on which matter, energy and time play out... Why it has negative pressure and 'expands' is still unknown: but we can say we observe that this is a characteristic of space-time.

I think that's about as far as physics will take you.

 

[Loren]

ARe you saying that this boundary is not fixed?

This is no boundary as such.

It's easy to think that way because in a classical sense your brain is hardwired to think that way, but it's not how it happens. The universe is not expanding into anything and as such there can not be a boundary.

Now, if you want to postulate about multiple universes or M-Theory and branes floating in a bulk, that's one thing and it's also a pretty wild theory at that.

There are arguments that the universe has a bounded size or an infinite size. Infinite is one thing as you can imagine the sum mass and energy of the universe spreading out into that infinite abyss.

If the universe is finite in size, then it is a little harder to wrap one's brain around because you naturally want to think it must be getting bigger into something or worse yet, that if you could theoretically travel at a straight vector you would reach a boundary, but you would not because what is straight will ultimately lead you back to where you started.

Finally, another misnomer is that because the universe is expanding then the space between all mass is also expanding. Not so. Gravity plays a role in keeping things together, so the Milky way is the same size, even though space is expanding and the universe is getting larger, just as the distance between your two ears remains constant.

 

[microtech]

Intriguing... What new physical force is it that "glues" the galaxies to this "space" thing, so they get "dragged along" as the "space thing" expands? It has to be way stronger than the gravity holding the galaxies in place to begin with... A second question that screams for an answer is: Where is all the energy coming from, that must fill the newly created (expanding) "space thing"? And as this energy (the "vacuum energy," a.k.a. the "zero point field") constitutes "information" (of sorts), it cannot possibly fill the newly created (expanding "space thing") faster that light... Intriguing, indeed.

 

[Drakkith]

Intriguing... What new physical force is it that "glues" the galaxies to this "space" thing, so they get "dragged along" as the "space thing" expands? It has to be way stronger than the gravity holding the galaxies in place to begin with...

There is no such force holding things in place. In General Relativity, this expansion is a result of the geometry of the universe, not because something is 'pinning' galaxies to space. This is kind of like how if you have two rockets, one heading one way and the other heading 45 degrees in another direction, the distance between them grows over time.

 

[microtech]

two rockets, one heading one way and the other heading 45 degrees in another direction, the distance between them grows over time

Of course: the rockets ar moving -- just how is that "rocket analogy" relating to galaxies (with (usually) very small "peculiar motion")? It would also be nice if you (or someone) could point me to the relativity equations that "predict" that "expansion at light speed" is taking place to begin with...

For the distance between two objects (in free space or whereever) to increase, one or both objects must be moving. If an object (like a galaxy) is not moving (zero peculiar motion), "expanding space" would maybe expand some imaginary "space bubble" containing that galaxy, but nothing in SR or GR says anything about matter "hanging on" to space.

And what about the much needed (according to QM) ZPF (vacuum energy)?

 

[Drakkith]

Of course: the rockets ar moving -- just how is that "rocket analogy" relating to galaxies (with (usually) very small "peculiar motion")?

It's just an example of geometry at work. Perhaps a poor example.

It would also be nice if you (or someone) could point me to the relativity equations that "predict" that "expansion at light speed" is taking place to begin with...

Sure. I believe what you want is the FLRW metic, the Friedmann equations, and the scale factor. You can look at Einstein's Field Equations too if you'd like.

For the distance between two objects (in free space or whereever) to increase, one or both objects must be moving. If an object (like a galaxy) is not moving (zero peculiar motion), "expanding space" would maybe expand some imaginary "space bubble" containing that galaxy, but nothing in SR or GR says anything about matter "hanging on" to space.

They are moving. Indeed, they are actually accelerating over time. But there is no force being applied to accelerate these objects. By force, I mean a force that an accelerometer could measure. Just like how accelerating in free falling under gravity cannot be measured with an accelerometer, neither can expansion. Both are the result of the geometry of spacetime. When we say that 'space is expanding', the actual mathematical effect is that the scale factor of the Friedmann equations is changing, which then affects the rest of the math accordingly.

And what about the much needed (according to QM) ZPF (vacuum energy)?

What about it?