View Full Version : What is space?
Philip7575
Nov16-11, 01:27 AM
I'm brand-new to this site, an English teacher, certainly not a physicist, but I'd sure appreciate some (gentle) help.
The short version of my question:
How can the universe expand into infinite space?
Are there two kinds of space? The first is the distances between galaxies in our universe, and the second, space, is something else?
Where did space come from? Was it there before the Big Bang?
If there is space and space, why isn't there time and time?
Tanelorn
Nov16-11, 09:43 AM
Hey Philip welcome to the Forum.
I have been full circle round this question here in this thread where I got lost on older Physics concepts such as the aether:
http://www.physicsforums.com/showthread.php?t=487911&highlight=properties+of+space
My conclusion is that space has no objective existence whatsoever in the same way that ponderable matter does. By itself it is just a measurement of the distance or the separation between two physical objects, similar to the separation between two points in time. It is also a framework in which ponderable matter can "hang". It is also a void through which force carriers can propagate, but it is the characteristics of the force carriers which determine the way in which they behave and interact with ponderable matter. I believe that this is the most modern view and it replaces the older concepts of space being an aether with properties of its own.
Philip7575
Nov16-11, 12:02 PM
I'm reading The Hidden Reality by Brian Greene. Here's his explanation (buried in a note at the bottom of p. 138): "If space were infinitely big, you might wonder what it means to say that the universe is larger now than it was in the past. The answer is 'larger' refers to the distances between galaxies today compared with the distances between those same galaxies in the past . . . . In the case of an infinite universe, 'larger' does not refer to the overall size of space, since once infinite always infinite. But for the ease of language, I will continue to refer to the changing size of the universe, even in the case of infinite space, with the understanding that I'm referring to changing distances between galaxies."
While physicists and cosmologists are usually precise, I can't grasp these two uses of the word space. One kind of space means one thing, and another space means something else.
Furthermore, I understand (I think) that if all matter and energy were removed from the universe, then time and space would vanish, too. But why wouldn't space disappear? And since General Relativity is about spacetime, why isn't there spacetime?
Tanelorn
Nov16-11, 12:16 PM
The distance between distant galaxies is increasing and accelerating due to dark energy. The universe is to al intents and purposes infinite, whilst the observable universe is finite and getting smaller all the time, due to expansion making the most distant parts no longer observable. I am not sure what you are confused about?
The distance between distant galaxies is increasing and accelerating due to dark energy. The universe is to al intents and purposes infinite, whilst the observable universe is finite and getting smaller all the time, due to expansion making the most distant parts no longer observable. I am not sure what you are confused about?
"to all intents and purposes" begs the question of IS it infinite or not, and that is a heavy discussion, not to be dismissed lightly even though you ARE right that it is irrelevant to our direct experiences.
I'm brand-new to this site, an English teacher, certainly not a physicist, but I'd sure appreciate some (gentle) help.
The short version of my question:
How can the universe expand into infinite space?
Are there two kinds of space? The first is the distances between galaxies in our universe, and the second, space, is something else?
Where did space come from? Was it there before the Big Bang?
If there is space and space, why isn't there time and time?
I don't think I could add anything to Tanelorn's excellent comments on space, I just wanted to add a note about the Big Bang. It is a highly controversial subject as to what, if anything, came before the big bang. The currently accepted model of cosmology basically says that we know a lot about what happened AFTER the singularity and absolutely nothing about the singularity itself or any possible "before" ("before" doesn't really exist in the standard cosmological model).
So you're next question HAS to be "how can something come out of nothing?". I can only suggest that you stock up heavily on headache pills and read about Quantum Mechanics.
Philip7575
Nov16-11, 05:12 PM
The--or maybe I should say "our"--universe is infinite? I'm paraphrasing from the Brian Green book, but one of the things we know pretty certainly is that the expansion of the universe is speeding up. That's what Perlmutter et al just got a Nobel Prize for.
Researchers have been able to calculate the cosmological constant--the amount of dark energy in the universe necessary to account for this expansion--by the simple algebra of flipping E=mc2 around to M=e/c2. The data from the faster-than-expected expansion requires a cosmological constant of just under 10-29 grams in every cubic centimeter of space.
The number of cubic centimeters in our universe is big, but it is not infinite.
The number of cubic centimeters in our universe is big, but it is not infinite.
You should not make definitive statements on this forum that you cannot back up with science. What you have stated is an unsupportable personal opinion. You MAY be right, but you may be wrong, and either way, you can't prove it, so stating it as fact is not a good idea.
Hi Philip7575
I can only suggest that you stock up heavily on headache pills and read about Quantum Mechanics.
Another way of getting a really good headache is to Google “Cosmic Topology.”
Philip7575
Nov16-11, 09:19 PM
phinds:
Jeez, I'm an English teacher. How could I possibly have a personal opinion about the cosmological constant or the size of the universe in cubic centimeters?
I'm paraphrasing Brian Greene's The Hidden Reality, p. 138 and p. 337 n. 8 and 9. Greene is a professor of physics and mathematics at Columbia University, and a well-respected populizer of tough science like this. His first book, The Elegant Universe, was a finalist for the Pulitizer Prize. And I'm getting that information from the book's dust jacket, so it's not "unsupportable personal opinion," either.
The point is that if researchers can calculate the cosmological constant by plugging the total amount of dark energy in the universe into that calculation, the total amount of dark energy must be finite. Put another way (and this is me, not Greene), if the universe were infinite, then the total amount of dark energy in it would also have to be infinite. Put still another way (me again, not Greene), if the universe were infinite how could it be expanding?
The point is that if researchers can calculate the cosmological constant by plugging the total amount of dark energy in the universe into that calculation, the total amount of dark energy must be finite. Put another way (and this is me, not Greene), if the universe were infinite, then the total amount of dark energy in it would also have to be infinite.
Makes sense to me.
Put still another way (me again, not Greene), if the universe were infinite how could it be expanding?
Not necessarily. 2 times infinite is still infinite.
Philip7575
Nov16-11, 11:11 PM
Imax: "2 times infinite is still infinite."
To cite Greene again, "In the case of an infinite universe, 'larger' does not refer to the overall size of space, since once infinite always infinite."
This is one of the things that led to my initial question. If the universe is infinitely large, then it can't get any bigger. So physicists talk about space in our finite universe at the same time they say our finite universe is expanding into infinite space.
It's these two uses, space vs. space that I don't understand.
[QUOTE=Philip7575;3620138]phinds:
Jeez, I'm an English teacher. How could I possibly have a personal opinion about the cosmological constant or the size of the universe in cubic centimeters?
QUOTE]
I would think an English teacher would understand that when you make a statement without quotes around it, folks will perceive you as being the author of the statement. You seem offended that I had that perception.
bill alsept
Nov17-11, 12:14 AM
How can the universe expand into infinite space?
Are there two kinds of space?
Where did space come from?
Was it there before the Big Bang?
Welcome to the forum Philip, I too am new at this and sometimes catch myself making factual statements that really need to be prefaced with "My Opinion is"
First of all there is only one kind of space. The space between galaxies is the same as the space inside atoms. There may be differences like temperature, density, fields etc. but space is space.
I believe the universe works in cycles so yes there would have been space before the Big Bang. Space from the last cycle would have condensed down to a singularity, during which time there would not have been any space.
I think the universe is formed from an finite number of extremely small particles. These particles may be condensed into matter as we know it or diffused to the point we can't see them. As they move in relation to each other they each form electromagnetic fields. I believe it is the combination of these fast moving particle and their fields that make space as we know it.
As for your first question, the universe is not expanding into space. Space IS what expands.
This is one of the things that led to my initial question. If the universe is infinitely large, then it can't get any bigger. So physicists talk about space in our finite universe at the same time they say our finite universe is expanding into infinite space.
It's these two uses, space vs. space that I don't understand.
There’s only one space. The space in our universe isn’t expanding into some other outside space. If the universe is finite, then travelling a straight line in any direction can bring you back to where you started. It’s just like here on Earth. The big difference is that space has 3 dimensions, whereas here on Earth, gravity restricts up and earth down.
Brian Greene gave a good description of expansion:
In the case of an infinite universe, 'larger' does not refer to the overall size of space, since once infinite always infinite. But for the ease of language, I will continue to refer to the changing size of the universe, even in the case of infinite space, with the understanding that I'm referring to changing distances between galaxies.
Mathematically, a finite space can expand, remain static, or contract. Our Universe seems to be expanding.
bill alsept
Nov17-11, 12:26 AM
Mathematically, a finite space can expand, remain static, or contract. Our Universe seems to be expanding.
I believe it expands and contracts but never static or the cycle would stop. And yes our universe does seem to be expanding but I wonder?
narrator
Nov17-11, 12:59 AM
Hi Philip, from one boffin to another, I'll give it a go at explaining. Not that long ago, I had a similar confusion.. what is expanding into what.. and I also ran into the "universe is infinite" conundrum. It eventually made sense to me, even though I haven't seen any of the math (and probably would struggle with it if I did).
What is finite? Our observable universe (OU) is finite. It is a spherical distance beyond which we cannot see. There are two reasons for this. The first is that the light from stars beyond that have not yet reached us. The second is (and this will be difficult, but more on it later) that the universe is expanding, faster than light, meaning that some of the light from beyond our OU will never reach us.
What is infinite? The whole universe, not just our OU, is believed to be infinite, according to the more popular models. As background to this, people also get confused with the Big Bang, thinking of it like an explosion that happened in one place and spread beyond that centre. The name, Big Bang, was given to it by one of its early detractors. The actual model says that when the BB occurred, it happened everywhere (infinitely), in the same instant.
What is expansion? Expansion, as has been said in this thread, is the growing distance between galaxies, but more specifically, between matter that is not bound by gravity to other matter. Just as our Moon is tied in orbit to us, and us in orbit to the Sun, so are galaxies tied to other galaxies. Expansion is putting more distance between galaxies that are not so bound.
An important intermediate point is to be understood about light speed (c). It is believed that nothing can travel faster than light, even galaxies relative to each other. Yet in this expansion, the distance between some galaxies is growing at faster than light speed. Sounds like a contradiction? I'll explain.
The distance between such distant matter is growing in two ways. The first way is their actual movement, relative to each other, a concept we readily understand from everyday experiences. The second way that the distance is growing is that dark energy is impacting on space-time in a way that effectively puts more distance between the two objects. Still confused? So was I.
The best way that cosmologists have attempted to represent, what is essentially a mathematical model, is by using a 2-dimensional analog of 3 dimensional space, by asking us to imagine that the universe is like a balloon. Travel anywhere on that balloon's surface and you will find no end point. Objects on the surface of the balloon will move relative to each other. Add air to that balloon, and the distance between objects grows, in part from their own movement and in part from the expansion of that balloon. So, add the slower than light movement of the objects, relative to each other, to the expansion, and you can see how the growth in distance can exceed the light speed limit.
As I say, this is my boffin explanation, much of which I've learned from the patient ones here. Our Earth-bound paradigms make it difficult to comprehend some of these ideas, but as they've rolled around in my head, I could see the logic.
Does that help at all?
Oops.. I just looked up boffin.. the online dictionary uses words like "scientist" and "expert". :blushing: I'm not a scientist, nor an expert - just someone who asks, listens and learns about this fascinating subject.
Narrator, that's a great explanation. Just to expand one point a little, it's VERY important to remember that the balloon analogy is JUST and analogy, and it's even more important to remember that you can only consider the surface of the balloon. People often look at the balloon analogy and start talking about the fact that it is a hollow shell with a center. In the analogy, you cannot consider the center; there IS no center, there is ONLY the surface.
I believe it expands and contracts but never static or the cycle would stop. And yes our universe does seem to be expanding but I wonder?
So you dispute the evidence that is believed by essentially all physicists? You might want to read up on the evidence a bit before you make such a cavalier statement.
Bread18
Nov17-11, 03:52 AM
I believe it expands and contracts but never static or the cycle would stop. And yes our universe does seem to be expanding but I wonder?
With the observation of the acceleration in the expansion of the universe, I don't see how it could slow down and contract, since this observation shows the exact opposite.
narrator
Nov17-11, 03:55 AM
With the observation of the acceleration in the expansion of the universe, I don't see how it could slow down and contract, since this observation shows the exact opposite.
As I understand it, it's still theoretically possible, though not so favoured a model, now that we know the expansion seems to be accelerating.
bill alsept
Nov17-11, 11:27 AM
So you dispute the evidence that is believed by essentially all physicists? You might want to read up on the evidence a bit before you make such a cavalier statement.
I'm not the first to wonder and hopefuly not the last.
bill alsept
Nov17-11, 11:31 AM
With the observation of the acceleration in the expansion of the universe, I don't see how it could slow down and contract, since this observation shows the exact opposite.
There was a time when no one could imagine the universe unless earth was at the center. There’s always other ways to interpret data.
Philip7575
Nov17-11, 12:27 PM
Some of these comments are getting off-track, but that's the nature of any blog.
To summarize (at least what's in my head):
Our universe is finite but expanding. The space in our universe, for example, the distance between galaxies, is also finite but expanding.
Our universe is expanding into something called infinite space.
And that's the ambiguity/imprecision: Space is used two different ways. No doubt, this is because of the limitations of language: There are many examples of phenomona, especially in quantum mechanics, that are impossible to visualize or grasp. This is another example.
Fair enough?
My conclusion is that space has no objective existence whatsoever in the same way that ponderable matter does. By itself it is just a measurement of the distance or the separation between two physical objects, similar to the separation between two points in time. It is also a framework in which ponderable matter can "hang". It is also a void through which force carriers can propagate, but it is the characteristics of the force carriers which determine the way in which they behave and interact with ponderable matter. I believe that this is the most modern view and it replaces the older concepts of space being an aether with properties of its own.
I am only a layman but my impression is that relativity says space can curve. And this has been verified by the fact that light from a distant star passing near a closer star will curve toward the closer star more than would be case in a "flat" space such as a Euclidian space as conceived by Newton. This is because the gravity of the intervening star is causing space to curve and light to follow its curved path. Space is therefore flexible and other than a simple void or a mere framework to hang things on. Also relativity says space is intimately linked with time in an entity properly called spacetime. Movement of an object through space quickly will slow that object's time down as compared with the passage of time on an object moving slower. This has also been verified by experiment with very accurate atomic clocks. Therefore it is difficult to speak of space at all without speaking also about time.
Tanelorn
Nov17-11, 03:25 PM
chaszz, yes I agree that the presence of large amounts of Matter (fermions) will interact with and bend light (photons). I think therefore that space appears curved to an observer, although there is no ponderable thing actually present in space which is being warped.
Also with the relativity experiment, I do not believe that anything present in space or space time is causing the effect, it is all a result of the effects of acceleration on the Fermions (matter) and Bosons (force carriers). I am saying all this in a rhetorical tone, I am just a old forgetful balding Engineer trying to rediscover Physics and learn about the latest theories of Cosmology :)
cephron
Nov17-11, 03:25 PM
Some of these comments are getting off-track, but that's the nature of any blog.
To summarize (at least what's in my head):
Our universe is finite but expanding. The space in our universe, for example, the distance between galaxies, is also finite but expanding.
Not quite...the "observable universe" - the tiny chunk of the universe that we can see - is finite. It's limited by how far light could have travelled in the amount of time that the universe has existed, with some extra complications thrown in by expansion. Basically, we can't see anything outside the observable universe because there hasn't been enough time for light from there to reach us. So the amount of the universe we can see is finite.
As for the actual whole of the universe? In a sentence, we don't know if it's finite or infinite. This has to do with the curvature of spacetime, and the current data isn't precise enough to pin down which it is. So we don't know right now, and people work with both models - sometimes right alongside each other. Better data in the future might give us a clear answer.
But yes - either way, finite or not, it is expanding.
And yes - the distance between any given galaxies is finite but expanding.
Our universe is expanding into something called infinite space.
And that's the ambiguity/imprecision: Space is used two different ways. No doubt, this is because of the limitations of language: There are many examples of phenomona, especially in quantum mechanics, that are impossible to visualize or grasp. This is another example.
Fair enough?
(Disclaimer: I am simply here transmitting conclusions which I understand to be true (from the FAQ, for example, which might help you), but have no knowledge of how to derive them)
No, there is no space outside the universe. The universe is not like a sphere, expanding at lightspeed into a bigger emptiness 'outside' of it. There is no 'outside' to the universe in the spacial sense. The universe, if it is infinite, has no edges. If it is finite, it also has no edges. This is similar to how the finite, 2d surface of the earth has no edges. Except in 3d, which is not as easy to visualize.
This much answers (I hope!) your questions. The wall of text below is more for fun.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(Disclaimer: now I am sharing an illustration I like to use, which is not based on data and is not accurate, but merely gives a sense of how a finite 3d space can have no boundaries/edges)
The way I like to visualize it is to imagine the universe as a cube filled with the stuff of the universe (superclusters of galaxies, filaments and voids, etc). You are in a transwarp spaceship inside of the cube (because you are in the universe). Pretend your spaceship goes as fast as you want, provided you clench your teeth and think really hard. ;)
So what happens if you fly out of the cube? Well, you don't, you simply come back in the other side. If you fly out the top side, you've just come up through the bottom side. If you fly out the east side, you've only just come in through the west, etc. So you can fly as far as you like any which way and you stay inside the universe.
Now, here's the cool part: you're not the only thing going out one side and coming in the other. The light (and gravity) radiated by all the stars, galaxies and whatnot also crosses sides in a similar way. So when you are approaching the east side of the cube, you are encountering the light that has just crossed the other way, going out the west side and coming in east. So you see ahead of you all the galaxies that are near the west side of the cube, even though you haven't left the east side yet. And when you actually cross out of the east side and come into the west, you are encoutering that same light. So when you "cross" from east to west, nothing changes visually. There is no jump or flicker in the image on your main screen. There wouldn't be any changes or brief interruptions in your ship's (or your body's) functioning. The transition would, if fact, be completely undetectable.
Crossing the "edges" of the universe is completely indistinguishable from not crossing them. Because of this, there is no way for you in your ship to map the "edges" of the universe, or find its center. In fact, you could pick any random point in the universe and arbitrarily define it to be the center, and figure out accordingly where the edges are, and it would work; you would have a functioning map. This is of course because, in fact, there are no edges - they are simply a useful device for us to visualize what we otherwise can't understand - that space just "wraps back in on itself". Mysteriously, as far as I'm concerned. ;) But there's math for people who want to get it.
Differences between this illustration and reality
I stress again that the above is only an illustration, and reality (even if we did have a spaceship that could fly as fast as we want) would behave differently. Here are some of the ways they differ...
1. In the illustration, space is geometrically what one would call a "3-torus", the 3d counterpart of the surface of a 2-torus, or doughnut shape. In reality, space is geometrically a 3-sphere, the 3d counterpart of the surface of a 2-sphere, or (basket-, soccer, tennis) ball shape. All the other differences listed are based on this difference. [PF veterans: if I screwed up any terminology here, please correct me!]
2. In the illustration, there are only six directions you can go that would bring you exactly back to where you started after "crossing the universe" once. That is, only if you go straight up, straight down, or straight north, south, east, or west. Visualize the cube: if you leave the center (works for any point, but take the center) going perfectly perpendicular to one set of faces of the cube, you will arrive exactly back at that point. If you leave the center going at a very slight angle instead, then you don't quite arrive back at the center after one lap. Depending on your angle, it could take an arbitrarily large number of laps to get back to the center. Not so with reality. Any direction you take will bring you back to your starting point with the same distance travelled.
To see the 2d analog of this, imagine a point on a doughnut's surface, say on the outer circumference. Only if you travel exactly around the outer circumference of the doughnut or exactly perpendicular to it will you end up back at your starting place. Travel any other angle, and you go crisscrossing all over the doughnut for who knows how long until you get back. Take a sphere, now, and select a point on its surface. From this point, you can travel any direction, and after 1 circumference-worth of travel, you end up back where you started.
3. (Directly following from 2.) In the illustration universe, there is actually something you could map by flying around, and that is the axes of the universe. A 3-torus universe would have 3 axes, which you could identify by finding out which directions, when flown, immediately bring you back to your starting point. In reality, there are no such axes, specifically because there is no difference in flying different directions.
[PF veterans: if you notice any other differences I missed, I'm curious to know what they are! Please do post them - thanks!]
chaszz, yes I agree that the presence of large amounts of Matter (fermions) will interact with and bend light (photons). I think therefore that space appears curved to an observer, although there is no ponderable thing actually present in space which is being warped.
Also with the relativity experiment, I do not believe that anything present in space or space time is causing the effect, it is all a result of the effects of acceleration on the Fermions (matter) and Bosons (force carriers). I am saying all this in a rhetorical tone, I am just a old forgetful balding Engineer trying to rediscover Physics and learn about the latest theories of Cosmology :)
Tanelorn, your interpretation of the facts is contrary to relativity, which is the currently accepted theory of space, time, acceleration and gravity. What you say in your first paragraph would lead to a Newtonian displacement of the light, which is considerably less than the Einsteinian (relativistic) displacement. General relativity predicted this and Eddington's landmark 1919 experiment confirmed the prediction to a high degree of accuracy.
The airplane experiment is another test which has supported relativity. This experiment uses constant speed in the airplane, not accelerated (increasing) speed, so your reference to acceleration is inaccurate.
Your theory using the fermions and bosons is interesting, but with all due respect I think you should remember that both the special and general theories of relativity have made predictions which have been borne out many, many times by experiments over the last hundred years or so. Many scientists have tried to prove these theories wrong but have not succeeded in doing so. This is whole orders of magnitude different from a private opinion unsupported by experimental proof.
THADONDARA
Nov18-11, 01:21 AM
Welcome philip Im also new to the forum and i'm so glad I found it. People here are nice and well informed and they know what they are talking about.
bill alsept
Nov18-11, 02:44 AM
Also with the relativity experiment, I do not believe that anything present in space or space time is causing the effect, it is all a result of the effects of acceleration on the Fermions (matter) and Bosons (force carriers).
What acceleration the fermions and bosons?
Tanelorn
Nov18-11, 09:23 AM
Bill and Chaszz, yes this is how I am interpreting what I have recently read. I could be mistaken in my interpretation, but when you remove all physical qualities and properties from the aether of space itself, all that is left is the characterisitics, properties, and interactions of the fermions and bosons themselves. Fermions and Bosons therefore ultimately have to be responsible for all observed phenonema. As I said before though, I need a professional Physicst to confirm this.
bill alsept
Nov18-11, 11:23 AM
Bill and Chaszz, yes this is how I am interpreting what I have recently read. I could be mistaken in my interpretation, but when you remove all physical qualities and properties from the aether of space itself, all that is left is the characterisitics, properties, and interactions of the fermions and bosons themselves. Fermions and Bosons therefore ultimately have to be responsible for all observed phenonema. As I said before though, I need a professional Physicst to confirm this.
My question was suppose to be
What accelerates the fermions and bosons?
Tanelorn
Nov18-11, 12:02 PM
A rocket ship is one possibility. You get angular acceleration just orbiting Earth.
G. E. Hunter
Nov18-11, 02:56 PM
Space is simply area. A location for matter and energy to be and travel. Air is different, it contains stuff - usually undetectably (not a word - i know) small for us to see. Please don't be rude if this doesn't help.
narrator
Nov18-11, 05:05 PM
Adding to Philip's question,
Is the expression "space-time" a bit of a misnomer? It brings with it a sense that space has some quality that acts upon matter. In discussions about expansion, the distinction between space and relative distance between bodies is always pointed out because space in and of itself has no quality that can act on matter. I'm not trying to be glib, but I'm guessing that perhaps because language is less precise than math, that expressions like space-time are more for the convenience of language than precision.
Matter, when in motion, acts on time. The faster some object goes relative to me, the slower its time elapses compared to my time. Protons fired near the speed of light in accelerators become more massive, heavier and harder to accelerate faster as they get closer to the speed of light. They are also flattened perpendicular to the direction of flight, so they become vertical ellipses, because their space is shortened in that direction. Particles called muons which have a known rate of decay, when fired in accelerators, take longer (in our time) to decay because their time slows down as they approach the speed of light. A large gravitational mass like the Earth bends the space around it, and also slows down time near it. These are some of the interdependent relativistic relationships of space, mass and time. They are why "spacetime" is more than a convenient way of expressing something about two unrelated entities. These relationships have been proven to exist many times in experiments of many different types. Before making generalizations about what space is and its relationship to time, I suggest you guys might want to read the stickies and the FAQ in the Relativity forum. I am a layman myself and know that it can be cutting to be spoken to this way, and I am sorry about it. But these forums are supposed to be places dealing with verified physical conclusions, not opinions.
narrator
Nov18-11, 09:35 PM
Before making generalizations about what space is
Mine is a "generalization" that has been repeated here many times in answer to questions. Space is nothing, has no effect on anything, and being nothing is not affected by anything, is basically the message. As one example, when talking about expansion, the oft repeated clarification is that expansion does not produce more space but more distance between objects, because space (being nothing) cannot be created.
But these forums are supposed to be places dealing with verified physical conclusions, not opinions.
Verified physical conclusion expressed within the bounds of language, which at times can be imprecise.
Tanelorn
Nov19-11, 09:56 AM
Space and Time are simply dimensions and Spacetime is the apparent warping of these dimensions as a result of the interactions of Bosons and Fermiions.
Space and Time are therefore not like ponderable matter, Space and Time are simply the total range of all possible locations.
According to the standard model of particle Physics all large scale, macro, physical phenomena, ultimately must be derived from the behaviour, characteristics and interactions of Bosons and Fermions.
The standard model of particle Physics is the fundermental heart of all of Physics which is itself the root from which all of science is derived.
I feel like a preacher of religion, but I really do mean this in a rhetorical tone. Also these views are still relatively young and so are still being tested.
Space is the area that matter occupies, we measure it by the yard and the second. Relative space-time we measure using a photon, our yard stick, and a clock, us.
juanrga
Nov19-11, 12:24 PM
I'm brand-new to this site, an English teacher, certainly not a physicist, but I'd sure appreciate some (gentle) help.
The short version of my question:
How can the universe expand into infinite space?
Are there two kinds of space? The first is the distances between galaxies in our universe, and the second, space, is something else?
Where did space come from? Was it there before the Big Bang?
If there is space and space, why isn't there time and time?
Universe is not expanding into infinite space.
There only a kind of space in the equations of the Big bang.
There are different speculations for what there was before the Big Bang, but none scientific hypothesis that can be tested.
Space and Time are simply dimensions and Spacetime is the apparent warping of these dimensions as a result of the interactions of Bosons and Fermiions.
Space and Time are therefore not like ponderable matter, Space and Time are simply the total range of all possible locations.
According to the standard model of particle Physics all large scale, macro, physical phenomena, ultimately must be derived from the behaviour, characteristics and interactions of Bosons and Fermions.
The standard model of particle Physics is the fundermental heart of all of Physics which is itself the root from which all of science is derived.
I feel like a preacher of religion, but I really do mean this in a rhetorical tone. Also these views are still relatively young and so are still being tested.
Relativity does not take its cues from the Standard Model of Particles or from Quantum Mechanics, nor do they take their cues from Relativity. These all may be regarded as fundamental theories though they cannot yet be reconciled with each other. This probably shows that all these theories are not yet fundamental enough and something better is waiting in the wings, for how long nobody knows. The String Theories are candidates, but so far without a shred of proof.
In the meantime, the Standard Model needs the Higgs boson to be found, which may happen in the Large Hadron Collider at CERN. If it is not found, there may be a lot of trouble in the Standard Model. So it is not quite fundamental in any sense as yet. Also many have remarked over the years at the large number of constants in nature that must be "just exactly so" for the Standard Model to work. It may, or may not be, showing cracks in its foundation.
Relativity also may have serious challenges presented to it in (1) The possible exceeding of the speed of light by neutrinos, and (2) quantum entanglement where communication between two particles appears to take place at faster-than-light speeds. So perhaps quantum mechanics, which has no such challenges currently, and is the most successful physical theory of all time, is winning the fundamental wars at this point. But it has little to say on space and time.
Perhaps we may agree to disagree here on the nature of space and time, whether they are real ponderable entities or not, since there are no true authorities to fall back on in "fundamental" theories that disagree with one another and cannot at this time be reconciled. I at any rate am willing to leave it there.
McCartney
Dec6-11, 01:05 PM
Bosons and Fermions:
Are they floating in space?
If space is expanding. Is there a dilution of Bosons and Fermions?
Is there a vacuum in space?
I would say that if there was a vacuum then space is nothing.
Can space expand into nothing?
Think of the Universe as having two possible shapes, infinite or finite. Imagine you’re on Earth and you’re going to travel the Universe in a space ship. You can start off in any direction but you have to travel in a straight line (i.e. a geodesic). If the Universe is infinite, then it doesn’t matter the direction you choose. You can never come back to where you started from. If the Universe is finite (i.e. compact), then you can choose a direction, following a space-like geodesic (i.e. straight line), and you will eventually come back to where you started from. Space doesn’t have to be expanding into nothing.
bill alsept
Dec7-11, 10:06 PM
Think of the Universe as having two possible shapes, infinite or finite. Imagine you’re on Earth and you’re going to travel the Universe in a space ship. You can start off in any direction but you have to travel in a straight line (i.e. a geodesic). If the Universe is infinite, then it doesn’t matter the direction you choose. You can never come back to where you started from. If the Universe is finite (i.e. compact), then you can choose a direction, following a space-like geodesic (i.e. straight line), and you will eventually come back to where you started from. Space doesn’t have to be expanding into nothing.
If the universe is finite then there is also the possibility that one would come to the edge of the universe. If this were possible then it could also be possible that the density out there would be low and time may be moving so fast out there that we or multiple generations could never live long enough to get there.
If the Universe is finite and forms a closed manifold, then it’s compact without boundaries. There doesn’t need to be an edge. The density of Bosons and Fermions can change locally, but their density could be globally homogeneous. If the Universe is finite and compact, then it could take a very, very long time to circumnavigate a closed space-like geodesic. Just because it could be closed does’nt mean that the Universe is small or static. It's possible that we or multiple generations could never live long enough to circumnavigate the Universe.
PatrickPowers
Dec8-11, 06:47 AM
I'm brand-new to this site, an English teacher, certainly not a physicist, but I'd sure appreciate some (gentle) help.
The short version of my question:
How can the universe expand into infinite space?
Are there two kinds of space? The first is the distances between galaxies in our universe, and the second, space, is something else?
Where did space come from? Was it there before the Big Bang?
If there is space and space, why isn't there time and time?
As far as anyone knows the Universe isn't expanding into anything. We don't know of anything outside of the Universe, more or less by definition.
When the Universe came into existence it was completely crammed with unthinkably dense stuff. Though for some reason it began to expand rapidly, there was no empty space whatsoever for quite some time.
According to Albert Einstein, time and space have no meaning unless there is matter and energy around. Matter and energy create time and space.
I believe that no one at this time has any idea what was there before the big bang.
McCartney
Dec8-11, 08:24 AM
As far as anyone knows the Universe isn't expanding into anything. We don't know of anything outside of the Universe, more or less by definition.
When the Universe came into existence it was completely crammed with unthinkably dense stuff. Though for some reason it began to expand rapidly, there was no empty space whatsoever for quite some time.
According to Albert Einstein, time and space have no meaning unless there is matter and energy around. Matter and energy create time and space.
I believe that no one at this time has any idea what was there before the big bang.
Einstein and Newton explained gravity; the former with more accuracy. However, I believe we really don't know what is gravity. We have read how mass bends the space, but we don't know how it happens. Sometimes it sounds like a fairy tale because it is hard to imagine such a thing.
Perhaps stars and planets in the universe are the equivalent of protons and electrons within an atom and they are somehow bound together by a force that we are trying to explain.
Sometimes it sounds like a fairy tale because it is hard to imagine such a thing.
Depends on your level of imagination.
Perhaps stars and planets in the universe are the equivalent of protons and electrons within an atom and they are somehow bound together by a force that we are trying to explain.
You are right that we don't know WHY gravity does what it does, but the mechanisms of WHAT it does are well understood and your "protons and electrons" analogy sounds like something from a 1930's science fiction story, not something from a science book.
McCartney
Dec8-11, 08:58 AM
Depends on your level of imagination.
You are right that we don't know WHY gravity does what it does, but the mechanisms of WHAT it does are well understood and your "protons and electrons" analogy sounds like something from a 1930's science fiction story, not something from a science book.
Is more than imagination when one can see the bending of light, however, all we have done is come up with an explanation and the explanation works very well.
LOL, at least it was the 1930s and not 1905. Thanks for your sarcasm:wink:.
The issue is we do not yet understand gravity.
PatrickPowers
Dec8-11, 09:16 PM
Einstein and Newton explained gravity; the former with more accuracy. However, I believe we really don't know what is gravity. We have read how mass bends the space, but we don't know how it happens. Sometimes it sounds like a fairy tale because it is hard to imagine such a thing.
I have read from reliable sources that General Relativity assumes inertia and derives gravity. At seems to be hard to say how this is derived, though.
Tanelorn
Dec9-11, 07:56 AM
My present understanding is that all macro forces and effects including gravity are as a result of the interactions of Bosons with Fermions and their residuals. The bending of space is simply an illusion because space itself has no objective existence. The same applies to spacetime and time.
McCartney
Dec9-11, 08:51 AM
My present understanding is that all macro forces and effects including gravity are as a result of the interactions of Bosons with Fermions and their residuals. The bending of space is simply an illusion because space itself has no objective existence. The same applies to spacetime and time.
One needs more than one area in space with mass to have gravity.
Gravity weakens with increased distance among objects. Do bosons and fermions behave differently when they are in close proximity to mass.
Is the boson and fermion network (or concentration) in the universe a constant?
Tanelorn
Dec9-11, 11:13 AM
McCartney please take a look at this page. It details the Fermions (matter) and Bosons (force carriers). This should help answer your questions.
http://en.wikipedia.org/wiki/Standard_Model
mgervasoni
Dec9-11, 06:16 PM
They say it's hard to imagine infinite space.. It could be a 4th dimension. BUT, if you did walk all the way to the edge of space and took one more step, you'd be right back where you started. It's like if someone couldn't grasp the concept of a 3 dimensional sphere. You'd put him on earth and he'd walk and walk and sooner or later he'd get right back where he started, bewildered. Thus may be our ability to conceive how we could get to the edge of space, and be right back where we were.
mgervasoni
Dec9-11, 06:19 PM
The protons and electrons acting like Solar Systems in the Bohr's atom model is what lead to all that science fiction in the 30's and after: universes within universes. Our modern concept of how atoms are and operate is very different from what you learned in highschool science.
They say it's hard to imagine infinite space.. It could be a 4th dimension. BUT, if you did walk all the way to the edge of space and took one more step, you'd be right back where you started. It's like if someone couldn't grasp the concept of a 3 dimensional sphere. You'd put him on earth and he'd walk and walk and sooner or later he'd get right back where he started, bewildered. Thus may be our ability to conceive how we could get to the edge of space, and be right back where we were.
I understand what you are saying but the "edge of space" is a very poor concept and should be avoided, since there isn't one.
There’s no need for an edge if the universe is finite or compact. It’s just like on Earth. You can travel in a straight line on Earth and you can come back to where you started from. The difference is that on Earth you’re limited to a 2D surface, but the Universe is 3D.
Bread18
Dec10-11, 05:26 AM
There’s no need for an edge if the universe is finite or compact. It’s just like on Earth. You can travel in a straight line on Earth and you can come back to where you started from. The difference is that on Earth you’re limited to a 2D surface, but the Universe is 3D.
That would happen if we lived in a closed universe and, as far as I know, there isn't any evidence for that.
mgervasoni
Dec10-11, 07:56 AM
I understand what you are saying but the "edge of space" is a very poor concept and should be avoided, since there isn't one.
Totally right Phinds, that was my point but perhaps poorly described. Just like there is no edge on earth, so is space/the universe... And again some people did think the Earth was flat/finite at one time which we just shake our heads at now.
And that's a very thought provoking statement that the Earth is 3D with a 2D surface, perhaps the universe is 4D with a 3D "surface"? (That's some string theory and other theories right?) Anyway, no need to speculate but it's a extremely interesting topic, and it's always good for our minds to think. :)
That would happen if we lived in a closed universe and, as far as I know, there isn't any evidence for that.
I’m trying to point out that there is no need for an edge, regardless of whether the Universe is finite or infinite. And, I agree with you. There is very little observable data indicating that it’s finite. Some models using Cosmic Microwave Background Radiation suggest that it may be finite, but I don’t think these are very conclusive. But, to quote Wiki (http://en.wikipedia.org/wiki/Big_Bang):
“According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly.”
How can you have rapid expansion in size if the Universe is infinite?
And that's a very thought provoking statement that the Earth is 3D with a 2D surface, perhaps the universe is 4D with a 3D "surface
It’s hard to imagine what a 3D Universe would look like embedded in 4D space.
.”
How can you have rapid expansion in size if the Universe is infinite?
Math involving infinity is NOT like normal math. If you double infinity what you get is EXACTLY the infinity that you started with.
Drakkith
Dec11-11, 06:03 AM
How can you have rapid expansion in size if the Universe is infinite?
The SIZE of the universe may or may not have increased. The distance between all objects in the universe did increase as a result of expansion. Is that easier to visualize? With an infinite universe, doubling the distance between all objects is exactly the same as in a finite universe.
The SIZE of the universe may or may not have increased. The distance between all objects in the universe did increase as a result of expansion.
The Big Bang theory postulates that the size of the Universe is increasing and it possibly starting from some kind of point singularity. The question is Space. Was Space finite or infinite near the time of the Big Bang event? Did the Universe start out in an infinite space with its entire mass confined in a very small volume, or did the big bang event itself create space?
I can’t help but think that the BB singularity had some properties similar to Black Holes, and Black Holes can bend space-time. It’s possible that space was compact near the Big Bang, with all the mass/energy of the Universe confined to a point singularity.
Drakkith
Dec13-11, 01:53 AM
The Big Bang theory postulates that the size of the Universe is increasing and it possibly starting from some kind of point singularity. The question is Space. Was Space finite or infinite near the time of the Big Bang event? Did the Universe start out in an infinite space with its entire mass confined in a very small volume, or did the big bang event itself create space?
To my knowledge the universe contains everything, including spacetime. Whether the size of the universe if finite or infinite is unknown.
I can’t help but think that the BB singularity had some properties similar to Black Holes, and Black Holes can bend space-time. It’s possible that space was compact near the Big Bang, with all the mass/energy of the Universe confined to a point singularity.
The Earth bends spacetime. So does my Dr. Pepper can sitting here on the desk next to me. A black hole only bends spacetime stronger than either of the former do. Also, as I have seen here on PF, supposedly most cosmologists don't believe an actual physical singularity existed, but that it is simply a consequence of having an incomplete theory.
The Big Bang theory postulates that the size of the Universe is increasing and it possibly starting from some kind of point singularity.
Absolutely not correct. There was NO "point" at which the BB happened, it happened everywhere. If there had been a point, the U would not exhibit the isotopy and homogeneity that are now observed.
I understand what you are saying but the "edge of space" is a very poor concept and should be avoided, since there isn't one.
Take a picture of any amount of time your camera will let you. We can make the illusion of photons going the opposite direction in time by making a negative. In this negative view the objects appear as holes and space the source of photons. Both pictures are of edges in my universe the edge is between inner space-time and outer space-time. Hope this helps.
Tanelorn
Dec16-11, 11:44 AM
Chalnoth, what are you thoughts on the following?
"If you were traveling at the speed of light and turned a flashlight on, what would happen to the light?
Relative to you, the light from your flashlight would still be moving at 3 x 10^8 m/s.
To allow this to happen, your perception of time slows down the faster you move and you gain more mass (E=mc^2)."
I believe the above is correct. So my question is, at the beginning of the BB when all particles were moving very fast, would time effects like the above example effect our estimates for the rate of inflation, or even our estimates for the age of the universe since particles were moving very fast for quite a while? I am very uncertain of which relativitic frames of reference apply in this case.
Thanks!
Take a picture of any amount of time your camera will let you. We can make the illusion of photons going the opposite direction in time by making a negative. In this negative view the objects appear as holes and space the source of photons. Both pictures are of edges in my universe the edge is between inner space-time and outer space-time. Hope this helps.
I do not wish to be rude, but this is just nonsense and has nothing to do with physics.
Chalnoth,
If you were traveling at the speed of light and turned a flashlight on, what would happen to the light?
Relative to you, the light from your flashlight would still be moving at 3 x 10^8 m/s.
Yep, that's right
To allow this to happen, your perception of time slows down the faster you move and you gain more mass (E=mc^2).
No, as you move faster, YOUR perception of time doesn't change at all, but an external observer sees your time as going slower [and you see theirs as going slower]
I believe the above is correct. So my question is, at the beginning of the BB when all particles were moving very fast, would time effects like the above example effect our estimates for the rate of inflation, or even our estimates for the age of the universe since particles were moving very fast for quite a while?
If it did, do you seriously believe that every physicist who has studied the early universe was to stupid that they overlooked it?
Tanelorn
Dec16-11, 12:12 PM
phnds, no need to be abrasive, I am not suggesting anyone overlooked anything or was being stupid!
Anyway I was hoping Chalnoth could give me his thoughts on this. thanks.
phnds, no need to be abrasive, I am not suggesting anyone overlooked anything or was being stupid!
Anyway I was hoping Chalnoth could give me his thoughts on this. thanks.
You're right ... I was snippy and I apologize. I'm always taken aback when someone comes up with an idea that just could not possibly have been overlooked and then rather than say something like "it seems to me that .... so why isn't that the case", they ask it as though they think no one has ever thought of it before.
Tanelorn
Dec16-11, 12:22 PM
I mostly expect to be completely wrong or missing a fundermental understanding when I ask these kind of questions, but at least I am still asking, which I think is a good thing.
I mostly expect to be completely wrong or missing a fundermental understanding when I ask these kind of questions, but at least I am still asking, which I think is a good thing.
I couldn't agree more that asking is a good thing, I was just put off by the particular way you asked, and again I apologize for being snippy.
Drakkith
Dec16-11, 02:22 PM
"If you were traveling at the speed of light and turned a flashlight on, what would happen to the light?
Relative to you, the light from your flashlight would still be moving at 3 x 10^8 m/s.
To allow this to happen, your perception of time slows down the faster you move and you gain more mass (E=mc^2)."
You cannot travel at the speed of light. Traveling arbitrarily close to c your perception of time would be vastly slower compared to "stationary" observers and distances would appear to you to be length contracted. However, you do not gain mass, you gain energy.
I believe the above is correct. So my question is, at the beginning of the BB when all particles were moving very fast, would time effects like the above example effect our estimates for the rate of inflation, or even our estimates for the age of the universe since particles were moving very fast for quite a while? I am very uncertain of which relativitic frames of reference apply in this case.
Thanks!
Are you referring to inflation? In that case I am unsure of the effects that expansion of space has with regards to relativity. Does time dilation apply between areas that are moving apart at .5c thanks to expansion or inflation?
If space was infinite before the Big Bang event and the entire mass/energy of the Universe was confined to a small volume and that volume expanded something like an explosion at the BB event, then it could be difficult to postulate a homogeneous and isotropic Universe. The outer regions of the Universe could see a very lower mass/energy density in the direction of expansion, as compared to a higher mass/energy density in the opposite direction. Given this scenario, it’s possible that the Universe wouldn’t be homogeneous and isotropic.
Seems to me that one way of having a homogeneous and isotropic Universe is if space is finite (i.e. compact).
If space was infinite before the Big Bang event and the entire mass/energy of the Universe was confined to a small volume
You can't have it both ways. Either space was infinite OR it was confined to a small volume.
If the U was infinite at its inception, that does NOT mean that it could not have expanded exactly as it did.
Drakkith
Dec18-11, 02:17 AM
If space was infinite before the Big Bang event and the entire mass/energy of the Universe was confined to a small volume and that volume expanded something like an explosion at the BB event, then it could be difficult to postulate a homogeneous and isotropic Universe. The outer regions of the Universe could see a very lower mass/energy density in the direction of expansion, as compared to a higher mass/energy density in the opposite direction. Given this scenario, it’s possible that the Universe wouldn’t be homogeneous and isotropic.
Seems to me that one way of having a homogeneous and isotropic Universe is if space is finite (i.e. compact).
The problem is that to the best of our knowledge the big bang was NOT an explosion like we normally think of. Whatever the size of the universe, infinite or finite, whatever, the big bang was the starting point. This includes spacetime.
Tanelorn
Dec19-11, 08:54 AM
In my earlier unanswered question I was asking if special relativity type effects have to be included in estimates for either the rate of inflation or even the age of the universe?
So I had a look around to see if photons which begin their journey in a higher density medium, with lower gravitational potential to a modern day lower density medium with higher gravitational potential, might undergo a red shift, and came up with the following:
Source: http://en.wikipedia.org/wiki/Self-creation_cosmology#Gravitational_red_shift
Gravitational red shift
The local conservation of energy, and the consequential variation in rest mass, demand that gravitational mass is treated under the de Broglie wave theory. Mass is defined by the DeBroglie frequency of that particle. The red shift caused by the curvature of space-time, a time dilation expressed by the metric component, is suffered not only by the photon but also by the atom with which it interacts and is thus undetectable. The red shift that is detectable is caused by the increase in rest mass that fundamental particles undergo when raised to the higher level. Gravitational red shift in this theory is interpreted not as a loss of gravitational potential energy by the photon but as a gain of gravitational potential energy by the apparatus measuring it. The red shift predicted is hence equal to the difference in Newtonian potential and thus identical with that of GR as confirmed in the Pound-Rebka experiment.
Firstly, I hope this is acceptable science and that it is ok to post this, I am finding that posting genuine science questions here is getting somewhat risky of terse replies.
So does this effect, if real, make any contribution to CMBR red shift and thus estimates for the age of the universe? Oh - and I am sure that if it does, that it has already been included.
I also saw at the end of the wikipedia article a section on Dark Matter which looked interesting. Is this view accepted science?
Tanelorn
Dec21-11, 11:50 AM
This page explains the concept of Gravitational Red Shift very well:
http://en.wikipedia.org/wiki/Gravitational_redshift
http://upload.wikimedia.org/wikipedia/commons/6/6d/Gravitational_red-shifting2.png
At the bottom there is also a discussion on gravitational time dilation:
Gravitational redshift versus gravitational time dilation
When using special relativity's relativistic Doppler relationships to calculate the change in energy and frequency (assuming no complicating route-dependent effects such as those caused by the frame-dragging of rotating black holes), then the Gravitational redshift and blueshift frequency ratios are the inverse of each other, suggesting that the "seen" frequency-change corresponds to the actual difference in underlying clockrate. Route-dependence due to frame-dragging may come into play, which would invalidate this idea and complicate the process of determining globally agreed differences in underlying clock rate.
While gravitational redshift refers to what is seen, gravitational time dilation refers to what is deduced to be "really" happening once observational effects are taken into account.
So is there anyone here who can speak to the level of contribution of gravitation red shift to the CMBR redshift and also the possible effect of gravitational time dilation on the estimated age of the Universe?
You can't have it both ways. Either space was infinite OR it was confined to a small volume.
It'is two different things. If you postulate that space is flat Euclidean and it can expand to infinity in all directions, it doesn’t preclude the possibility that the entire mass/energy of the U could occupy a finite volume near the Big Band event. What I’m trying to point out is that the BB event is unlikely to be something like an explosion, something you could expect from detonating dynamite. If this was the scenario, then it could be difficult to have a model of the U that was homogeneous and isotropic.
We are embedded within the BB event. A compact space model of the Universe can allow for closed space-like and closed light-like geodesics. A compact space model can explain a U that is homogeneous and isotropic.
And to all PF participates, Merry Christmas and Happy New year!
Drakkith
Dec22-11, 12:43 AM
It'is two different things. If you postulate that space is flat Euclidean and it can expand to infinity in all directions, it doesn’t preclude the possibility that the entire mass/energy of the U could occupy a finite volume near the Big Band event.
If I'm not mistaken, it isn't that it can expand to infinity, it's that it IS infinite. Or might be.
... it doesn’t preclude the possibility that the entire mass/energy of the U could occupy a finite volume near the Big Band event.
I contend that if it starts off not infiite it ends up not infinite. Do you disagree? How do you get from finite to infinite in a finite amount of time? Seems like a good trick to me
If I'm not mistaken, it isn't that it can expand to infinity, it's that it IS infinite. Or might be.
well, my point is more that it EITHER is or it isn't, and you can't have both. If it isn't at the start, then it isn't now and if it is now then it was at the start.
Drakkith
Dec22-11, 01:19 AM
well, my point is more that it EITHER is or it isn't, and you can't have both. If it isn't at the start, then it isn't now and if it is now then it was at the start.
Agreed.
I contend that if it starts off not infinite it ends up not infinite. Do you disagree?
No. Absent some kind of bizarre event, something like quantum symmetry breaking, then a U that was finite near the BB should be finite now. If space was infinite then, it should be infinite now.
My inclination is a U with a compact space (i.e. finite).
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