Space Density

[Dook]

Each time we look deeper into space we find more stars and galaxies.

Perhaps the universe is much, much, larger than we believe.

If so, maybe the universe is more dense towards the center and light travels at a different speed?

 

[Ophiolite]

Which centre was that then? Since when did the Universe acquire a centre?

 

[russ_watters]

Large-scale surveys (such as Hubble Deep Field) show clusters and superclusters, but they are consistent with the idea that there is no center. Things like the microwave background imply that the density is relatively uniform.

 

[Phobos]

Perhaps the universe is much, much, larger than we believe.

Virtually everyone agrees that there is more universe out there than we can see. And many scientists believe the universe to be infinite.

If so, maybe the universe is more dense towards the center

As noted above, the universe has no center (or edge) in 3D space. The Big Bang was a rapid expansion of all space, not an explosion from some center into emptiness.

and light travels at a different speed?

Light speed is constant (see Einstein's Relativity)

 

[Dook]

Light speed is not constant through something more dense.

 

[Castlegate]

Large-scale surveys (such as Hubble Deep Field) show clusters and superclusters, but they are consistent with the idea that there is no center.Things like the microwave background imply that the density is relatively uniform.

Since when is this an implication that the universe has no center? Uniform density doesn't imply anything one way or the other. Perhaps you can explain your logic.

 

[Chronos]

SDSS, and other studies, show no statistically significant overdensities at large scales. In other words, matter is uniformly distributed in every direction no matter where you are located in the universe. No professional astrophysicist, to my knowledge, seriously entertains the idea of a 'center' to the universe. The very concept of a center requires edges to make it meaningful. While the universe is believed to have a temporal edge [i.e., the age of the universe], it is not absolute and differs depending upon your location in the universe. It is therefore not physically meaningful. The CMB reference merely points out there is no preferred direction in CMB, which would be expected in a universe with fixed spatial edges.

 

[Facial]

If I remember correctly, the average density of space is something on the order of one atom per cubic centimeter.

 

[Mariko]

My astronomy teacher explained it like, everything is equally close or far no matter where you are in space to the big bang..

 

[varsha]

Which centre was that then? Since when did the Universe acquire a centre?

have a look at http://www.umich.edu/~gs265/bigbang.htm"

At the point of this event all of the matter and energy of space was contained at one point

Another consequence is that the universe is expanding in every direction. This observation means that it has taken every galaxy the same amount of time to move from a common starting position to its current position.

common starting position to it's current position
doesn't this mean that the universe has a center?

 

[russ_watters]

Since when is this an implication that the universe has no center? Uniform density doesn't imply anything one way or the other. Perhaps you can explain your logic.

In order to have a center, it must also have an edge. Since no edge is visible: no center.

The consistency of expansion is also evidence of a lack of a center.

 

[russ_watters]

have a look at http://www.umich.edu/~gs265/bigbang.htm"

common starting position to it's current position
doesn't this mean that the universe has a center?

No, it doesn't. Imagine an expanding balloon - the surface of the balloon has no edge or center. If the balloon could shrink, it would end up as a single point, but the surface would never have a center.

 

[rtharbaugh1]

I would suggest that the problem has more to do with our representation of the big bang that with any actual observation of the universe. If one looks at the usual inflation diagram, it certainly does look as if there is a center, as well as edges. Even the most recent reports about the first trillionth of a second are shown as if there is a center. These representations are misleading.

Of course people who have studied futher realize that the diagrams are spacetime diagrams, not merely space diagrams, but that is not clear to the average reader. And they are flawed, IMO, even as spacetime diagrams, since they never seem to account for the compression of time at the so-called first instants. One would think that the measure of time is the same from beginning to end, but that is not so.

R

 

[Castlegate]

In order to have a center, it must also have an edge. Since no edge is visible: no center.

Seems like flawed logic to me. This is not to say the opposite is true, but that there is no preference.

The consistency of expansion is also evidence of a lack of a center.

How so? I could just as easily explain a model with a center, with consistency of expansion. Again I see no preference here.

 

[rtharbaugh1]

russ watter's logic seems ok to me. How will you define the center if there is no edge?

I would like to see the explanation of a model with a center and consistancy of expansion. I don't get any physical image from this choice of words.

R

 

[Castlegate]

russ watter's logic seems ok to me. How will you define the center if there is no edge?

Well if I take two guys and put em in the center a room with no light, where one guy says there are no walls, and the other guy says there are, wherein these two dudes can't take more than one step in a direction, and that step leaves them shy of finding out if there are any walls to be found. Do you accept the guys statement that there are no walls, or the one that says that there is?

Clearly the guy saying there are no walls would be making an educated guess, but in this particular scenerio he would be dead wrong, while the guy saying there is a wall has nothing to go on but pot luck.
In the case of the universe having no center ...The educated guess is that there is no center, but by no means do we have a slam dunk.

I would like to see the explanation of a model with a center and consistancy of expansion. I don't get any physical image from this choice of words.

R

Imagine a thousand black dots on a white screen monitor equally spaced, wherein all dots move away from the center dot on the screen, and imagine that the further away each of these dots are from the center dot ... the faster they move from the center dot. In this scenerio no matter which dot you choose ... all dots will be seen to be moving away from the dot you choose, and with a consistancy of expansion overall.

 

[russ_watters]

Seems like flawed logic to me. This is not to say the opposite is true, but that there is no preference.

Please explain: how can there be a center if there is no edge? I suppose there could be an edge that we can't see, but in science the default assumption is always that if you don't have any evidence to say that something exists, you must assume that it doesn't. Besides, there is also the next point...

How so? I could just as easily explain a model with a center, with consistency of expansion. Again I see no preference here.

I probably could have worded that a little more descriptively, but what I mean is that if there were a center, the motion of galaxies could be plotted in 3d and their directions extrapolated back to a central point. But in fact, if you tried this, every galaxy would appear to be the central point.

Ie, if you look at galaxies in the direction of the center, they'd be denser and moving slower. If you look at galaxies in the opposite direction of the center, they'd be less dense and moving faster. Like an explosion.

 

[russ_watters]

Well if I take two guys and put em in the center a room with no light, where one guy says there are no walls, and the other guy says there are, wherein these two dudes can't take more than one step in a direction, and that step leaves them shy of finding out if there are any walls to be found. Do you accept the guys statement that there are no walls, or the one that says that there is?

For the purpose of science, both are correct in that the hypotheses are supported by their observations. You cannot assume the existence of something for which there is no evidence.

Clearly the guy saying there are no walls would be making an educated guess, but in this particular scenerio he would be dead wrong, while the guy saying there is a wall has nothing to go on but pot luck.
In the case of the universe having no center ...The educated guess is that there is no center, but by no means do we have a slam dunk.

Well, with all the other evidence, yeah, it's pretty much a slam-dunk.

Imagine a thousand black dots on a white screen monitor equally spaced, wherein all dots move away from the center dot on the screen, and imagine that the further away each of these dots are from the center dot ... the faster they move from the center dot. In this scenerio no matter which dot you choose ... all dots will be seen to be moving away from the dot you choose, and with a consistancy of expansion overall.

No, that isn't correct. For a dot a little to the right of center, looking to the left it will find dots closer together and moving slower than when it looks to the right: just like in an explosion. (edit: not sure about the velocity distribution, but I am sure of what it does for density...I'll work on that, though)

 

[rtharbaugh1]

"in the center a room with no light"

My question to you was, how can you know there is a center if there is no edge? In fact you could generalize the argument, as you have here, and assume that there could be edges but you cannot detect them, but the question is not really about the edges, it is about how you know there is a center.

Your placing two guys in the center of a dark room starts out saying there already is a center, so your statement is like saying "I know there is a center because two guys are standing there." Of course it is likely that in an otherwise empty room, one of the two guys is you, and the other is me. Now we still have an argument. You say there is a center because you are standing on it. But I argue that I could just as well be the center, and in fact, moreso, that everywhere around us is equally likely to be center. Then since there is no place that is more likely to be the center than any other place, your statement is "I am the center of the universe", and my argument (well, I won't speak for russ waters, but maybe he would agree with me here) is that since I have no evidence of a center in any particular place I cannot say that any particular place is the center, not even the place where I myself stand. So your argument is that you are the center of the universe, and my argument is simply that you are not the center of the unverse. Neither of these arguments can be proven, but your claim to be some special being among all the other beings, being in the center of the universe, will require some substantial evidence if you are not to be, universally by everyone except yourself, thought to be mistaken.

Moreover, if you persist in your argument, you will come into contact eventually with someone else who also claims to be the center of the universe. Is it worth fighting over? Maybe both of you will think so and get in a fist fight. I wouldn't like to see that, but it is an amusing thought.

On the other hand, if russ waters and I happen to meet and discuss this or some other issue, the chance of our getting in a fist fight is rather small. I hope so any way. Both of us can easily agree that there is no detectable center.

Now you really must think about the density question carefully. No matter which direction we look in space, and no matter how far away to the limit of our ability to discriminate, the universe looks the same. That is a startling fact, and you are right to think that it seems very unlikely. But all the evidence says it is the same, no matter where you go, or how long ago, or, for all we know, how far you get to go into the future.

Richard

 

[russ_watters]

No, that isn't correct. For a dot a little to the right of center, looking to the left it will find dots closer together and moving slower than when it looks to the right: just like in an explosion. (edit: not sure about the velocity distribution, but I am sure of what it does for density...I'll work on that, though)

Ok, I was thinking about this more and yeah, I was right about the velocity distribution too. The reason is the overall gravitational field of the universe has a similar effect in the accepted model and in your explosion model: the expansion slows down with time. But in the accepted model, since the gravitational field is uniform, the slowdown is uniform. In the "explosion model", since the gravitational field has a center, objects closer to the center will be slowed more than objects further away and thus you will see different velocities for the same distance if you look toward and away from the center.

 

[rtharbaugh1]

I have two ways to look at the expanding universe question. Perhaps there is only a limited amount of matter in the universe, so as the universe expands the matter gets farther and farther apart. Or perhaps there is more matter made somehow to prevent the matter in the universe from getting thin.

Now in SR and QED, there is no preferred universal time. Instead, time is a count of interactions. Each interaction is a tick of the clock of the interacting objects. So two photons can be made in one single interaction, then have different histories of interactions with other particles as they radiate, and then at some later place they might meet up again, with one of them "older" than the other, even though they were made co-instantaneously in a single event. QED uses this kind of time relativity to explain the actions usually taught as Snell's law of refraction.

So, if the universe has a fixed amount of matter, it thins as it gets older and larger, and so particles will be less likely to tick each other off. We might expect to see particles in the thinner regions of the universe experiencing less time. However we do not see thinner regions of the unverse, beyond a certain scale. There are variations, but they turn out to be local. On a large scale, we can see that the universe is the same density in all directions.

So, again, we are left with a difficult choice. If the universe is expanding, but not getting less dense, then there must be some unexplained mechanism for producing new matter, not at anyone place or center, as in the hypothetical "white hole", but everywhere at once.

Here is a link showing the concentration of matter in the observable universe.

http://www.anzwers.org/free/universe/index.html

or

http://www.atlasoftheuniverse.com/

(they are moving the site to the second address)

R.

 

[Castlegate]

No, that isn't correct. For a dot a little to the right of center, looking to the left it will find dots closer together and moving slower than when it looks to the right: just like in an explosion. (edit: not sure about the velocity distribution, but I am sure of what it does for density...I'll work on that, though)

Ok, I was thinking about this more and yeah, I was right about the velocity distribution too. The reason is the overall gravitational field of the universe has a similar effect in the accepted model and in your explosion model: the expansion slows down with time. But in the accepted model, since the gravitational field is uniform, the slowdown is uniform. In the "explosion model", since the gravitational field has a center, objects closer to the center will be slowed more than objects further away and thus you will see different velocities for the same distance if you look toward and away from the center.

My mistake not to include some other information with the initial model. I should have said that the dots are not all made at the same time. The first dot made is the center one. Imagine the first dot being made. Let's put a circle around the first dot and call it the dot maker. Now expand that circle outward from the center dot at a steady pace. Let this circle dump off dots as it moves outward at a steady increment so as to leave dots pretty much equally spaced. Let all dots dropped off move away from the center dot at the same velocity. Let gravity do it's thing.

Dots closest to center will have a slower speed away from center than the dots farther from center (over time). Observation from any dot will see all dots moving away, but there will be a difference between a dot close to center and one that is furthest from center.

In our universe the Earth would be close to center, but this should be of no surprise, because all dots eventually are close to center over time in an ever expanding dot making circle.

 

[russ_watters]

My mistake not to include some other information with the initial model. I should have said that the dots are not all made at the same time. The first dot made is the center one. Imagine the first dot being made. Let's put a circle around the first dot and call it the dot maker. Now expand that circle outward from the center dot at a steady pace. Let this circle dump off dots as it moves outward at a steady increment so as to leave dots pretty much equally spaced. Let all dots dropped off move away from the center dot at the same velocity. Let gravity do it's thing.

Continuous creation of particles in the universe? Didn't we already cover what the scientific method has to say about assumptions for which there is no evidence? You aren't serious, are you?

Dots closest to center will have a slower speed away from center than the dots farther from center (over time). Observation from any dot will see all dots moving away, but there will be a difference between a dot close to center and one that is furthest from center.

Right: and that is not what is observed. when looking around, we see no difference in velocity or density, regardless of which direction we look. Therefore your model is not the way the universe really is.

Wouldn't it be easier to accept the existing model, since it works and fits the evidence we have, than to try to create a new model that satisfies your preconceptions? Isn't it possible that your preconceptions are wrong?

 

[Castlegate]

Continuous creation of particles in the universe? Didn't we already cover what the scientific method has to say about assumptions for which there is no evidence? You aren't serious, are you?

Quite serious. rtharbaugh1 asked for an explanation of the model with a center and consistancy of expansion. I posted it. It works in accordance with observation and that's that. If you don't understand it ... Perhaps my words weren't chosen all that carefully, and the fault is entirely mine, or you haven't given it the time of day and that would be your fault, and without saying to much - quite possibly your loss.

And why would continuous creation be harder to buy than the creation of all there is in one feld swoop.

Wouldn't it be easier to accept the existing model, since it works and fits the evidence we have, than to try to create a new model that satisfies your preconceptions? Isn't it possible that your preconceptions are wrong?

I could sit in a chair and wait for something to come along on a silver platter, but choose get up on my feet and look around. What else you going to do? Mull over what's been hashed over for decades on end? I could be completely wrong by which I would still be walking around looking for something else. Can't look under a rock if it's 50 feet from my chair now can I?

The Big Bang model is falling apart slowly but surely. Unexpected observations crop up on a regular basis. The farther we pierce into space the worse it gets. Five or ten years from now it's going to start to look like a bad dream. Twenty years from now it's going to get canned, and yes this is another assumption.

 

[Ophiolite]

common starting position to it's current position
doesn't this mean that the universe has a center?

You are missing the point: the point that the Universe emerged from in the Big Bang. It was everywhere. Everywhere is the centre. Wherever you observe from within the Universe it all looks pretty much the same. The centre is everywhere, which is another way of saying there is no centre.

Remember that it is space that is expanding in the Big Bang. It is not a bunch of matter and energy expanding into a pre-existing space.

 

[russ_watters]

Quite serious. rtharbaugh1 asked for an explanation of the model with a center and consistancy of expansion. I posted it. It works in accordance with observation and that's that. If you don't understand it ... Perhaps my words weren't chosen all that carefully, and the fault is entirely mine, or you haven't given it the time of day and that would be your fault, and without saying to much - quite possibly your loss.

I understand it just fine. The problem (as I've said several times) is it adds assumptions for which there is no evidence and is therefore invalid as a scientific theory.

And why would continuous creation be harder to buy than the creation of all there is in one feld swoop.

Simple: There is evidence for a single creation and there is no evidence for continuous creation. You are chasing idle speculation.

 

[Ophiolite]

Simple: There is evidence for a single creation and there is no evidence for continuous creation. You are chasing idle speculation.

It wasn't idle speculation fifty years ago.

 

[selfAdjoint]

It wasn't idle speculation fifty years ago.

It was speculation in the absence of a key piece of evidence; the CMB. When that was discovered, the main proponents of CC conceded. There were and are the determined die-hards, but you always have that, and they are always behiind the observational curve, see for example the latest WMAP results.

 

[Ophiolite]

I am objecting to you characterising the then standard, widely accepted Steady State comological model, with its attendant spontaneous creation, as speculation. It was not speculation prior to Penzias and Wilson, it became invalid as a consequence of Penzias and Wilson.

 

[SpaceTiger]

I am objecting to you characterising the then standard, widely accepted Steady State comological model, with its attendant spontaneous creation, as speculation. It was not speculation prior to Penzias and Wilson, it became invalid as a consequence of Penzias and Wilson.

It's true that steady state hasn't always been crackpot territory and some theory was developed for it back in the day. Some of the basic ideas behind it are still possible -- an infinite universe, multiple creations, an infinite timeline -- but we're sure at this point that the universe is expanding.

 

[russ_watters]

I'm an engineer, not a scientist, but my perspective on the scientific method is that when the evidence truly is thin (ie, when GR was just a baby), speculation is fine. When, say, the evidence only gives you 20% confidence in a new theory (allowing, in that 80%, room for other theories), then it is speculative and there isn't anything wrong with that if understand and accept the tentative nature of a theory. (examples: string theory, black holes 20 years ago) But if you discover more things that allow you to gain, say, 90% confidence in a theory (allowing only 10% room for other theories), then it becomes less acceptable to speculate on something that requires something that only exists in that 10%.

I think it is fair to say that most scientists have more than 90% confidence in the basic idea of the BBT.

 

[ray b]

if you go here
http://www.voanews.com/english/2006-03-17-voa16.cfm [Broken]
about the wmap data

there is a picture called "Time line of the Universe"

now that's a space time picture BUT
if it is real and is a slice thru the shaped like a ball universe
then SOMETHING is near an edge and something else in near the center
a one observer near the edge would see a blank space if they looked out ward [in to what I call the "NOT YET" beyond our current space]
while the observer in the near center would see a equal veiw to ours
there for we should be nearer the center then the edge
even if we can't see or get to that edge to there by find the center
that should be equidistant to all the edges
or there are a lot of smoke and mirrors
because everywhere can't be the center
and somewhere must be near an edge

 

[ray b]

and back to the thread point
in addition to the one atom
there should be 5 units of dark matter
and 14 of dark energy what ever they are

 

[Chronos]

Quite serious. rtharbaugh1 asked for an explanation of the model with a center and consistancy of expansion. I posted it. It works in accordance with observation and that's that. If you don't understand it ... Perhaps my words weren't chosen all that carefully, and the fault is entirely mine, or you haven't given it the time of day and that would be your fault, and without saying to much - quite possibly your loss.

And why would continuous creation be harder to buy than the creation of all there is in one feld swoop.

In the post big bang universe, the laws of thermodynamics are the supreme court of physics. Article I of the thermodynamics constitution states 'Matter cannot be created or destroyed, only transformed.' In other words matter can be converted to energy and vice-versa, but no loss or profit in this transaction is possible. There is not a shred of evidence suggesting this rule has ever been violated. The laws of thermodynamics cannot, however, be applied to the big bang itself. They, like the other laws of nature [e.g., gravity] were emergent - which is to say they came into being as a consequence of the big bang. To illustrate this point, we even have a very good idea regarding the order in which the laws of the universe emerged.

I could sit in a chair and wait for something to come along on a silver platter, but choose get up on my feet and look around. What else you going to do? Mull over what's been hashed over for decades on end? I could be completely wrong by which I would still be walking around looking for something else. Can't look under a rock if it's 50 feet from my chair now can I?

You could, but that is not how physics works. We routinely look under 'rocks' that are billions of light years away from our 'chairs'. Not like we see all that is possible to be seen, but enough to make very solid predictions about what is and is not likely to be seen.

The Big Bang model is falling apart slowly but surely. Unexpected observations crop up on a regular basis. The farther we pierce into space the worse it gets. Five or ten years from now it's going to start to look like a bad dream. Twenty years from now it's going to get canned, and yes this is another assumption.

Your agenda is showing here - BB bashing. The BB model has greatly strengthened over the years, not diminished. The 'rogue' observations that are occasionally reported are overwhelmed by the sheer number, and superior quality, of corroborating observations. For a recent example see:

Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
http://www.arxiv.org/abs/astro-ph/%200603449 [Broken]

 

[Castlegate]

In the post big bang universe, the laws of thermodynamics are the supreme court of physics. Article I of the thermodynamics constitution states 'Matter cannot be created or destroyed, only transformed.' In other words matter can be converted to energy and vice-versa, but no loss or profit in this transaction is possible. There is not a shred of evidence suggesting this rule has ever been violated. The laws of thermodynamics cannot, however, be applied to the big bang itself. They, like the other laws of nature [e.g., gravity] were emergent - which is to say they came into being as a consequence of the big bang. To illustrate this point, we even have a very good idea regarding the order in which the laws of the universe emerged.

I agree that this law will not be broken, however continuous creation in the model I was discribing... this law is an ( emergent), which is to say it came into being as a consequence of the continuous creation.

Your agenda is showing here - BB bashing.

Ya think?