Size and Age of the Universe

[GoBears]

I think many people assume that the BB took place in an infinite space, and that matter and energy expanded from a tiny point--a singularity--into an existing matrix of empty space, and continues to fill that space as it expands into infinity.

I have always thought of the BB as an actual expansion of space. In other words, the BB arose as a singularity in something other than the spacetime we (think we) know and that there is nothing (at least nothing it is possible for us to observe) outside our spacetime. I think we live in an 11 (or more) dimensional hypersphere with a diameter (for lack of a better word) of 14 billion or so LYs. It is simply not possible for us to know what is "outside" our hypersphere. I doubt if even God can know what is outside our hypersphere!

Early in the discussion, 50bmg asked about two galaxies, each 14 billion LYs in opposite directions from Earth. My guess is that, since we observe them as they were 14 billions years ago, they are actually quite close to one another on the opposite side (for lack of a better word) of the hypersphere from us.

If there were some magical way to "see" more than 14 billion LYs, we could probably look across the hypersphere and "see" ourselves 28++ billion LYs away. There is a phenomenon in radio where you can hear the echo of your own signal a fraction of a second later after it goes around the Earth. This phenomenon is a 3D analog to an 11D "look" across the hypersphere of spacetime.

[dougettinger]

So the geometry of the universe is or can expand faster than the speed of light?

Yes.

Isn't that expansion a measured quantity? Is that quantity less than c?

It is measured. Hubble's law tells us that the rate of separation between two points is a function of their separation. Get far enough apart, and those points will be separating faster than c. In fact, that's what defines the size of the observable Universe. Points outside the observable Universe (which is different for every point) are simply moving faster than c, and are therefore causally disconnected.

In fact, there is no physical law being broken by two objects moving apart faster than c. The rules only require that information can't be transferred between them in that case.

What you are saying is that matter somewhere in the non-observable universe can move faster the velocity of light, c. I always thought that very strange things occurred to matter if it traveled at or beyond the velocity of light.(?)

So an interesting question comes to mind. If humans are living in one of these galaxies traveling faster than the "c"; and since velocity has direction, then observers in these galaxies would only see other galaxies only in one direction or a 180 degree hemisphere. And as this galaxy went faster and faster, an observer would eventually only be able to see galaxies directly ahead in the path of travel. Is this thought experiment correct ? If one residing on one of these galaxies shines a flashlight in the same direction as this moving galaxy (faster than c) assuming all other velocity vectors are resolved, can the photons ever emit from the flashlight ?

Or perhaps photons are always accelerating by a small amount not measurable in our small part of the universe. Or perhaps a new time dimension has been entered.

Doug Ettinger
Pittsburgh, PA

[BMAONE23]

Old school math
Two Bullet trains are moving in opposite directions at 390 MPH. Relative to each other, the trains are separating at 780 MPH, faster than the speed of sound yet neither is breaking the sound barier.
Something like this?

[rstevenson]

So an interesting question comes to mind. If humans are living in one of these galaxies traveling faster than the "c"; and since velocity has direction, then observers in these galaxies would only see other galaxies only in one direction or a 180 degree hemisphere. And as this galaxy went faster and faster, an observer would eventually only be able to see galaxies directly ahead in the path of travel. Is this thought experiment correct ?

I don't think so. Think of it this way: our Milky Way galaxy is moving through its local space at a speed which is only a tiny fraction of c, yet it is separating from galaxies outside our observable Universe at c or even faster. "Separating" due to the expansion of space is not the same as "velocity" in the sense you're describing.

Rob

[Chris Peterson]

What you are saying is that matter somewhere in the non-observable universe can move faster the velocity of light, c. I always thought that very strange things occurred to matter if it traveled at or beyond the velocity of light.(?)

It doesn't mean anything to say that some bit of matter is moving faster than the velocity of light. There is no such thing as absolute velocity- it is a relative thing. So you can say that some bit of matter is moving faster than the velocity of light with respect to some location in the Universe, or with respect to some other bit of matter (which is, in fact, what I said in the post you quoted).

Nothing odd happens to matter when it moves at the speed of light with respect to something else. The strange things you are talking about involve how that fast moving bit of matter behaves as seen from some other reference frame. From its own reference frame, it might as well be at rest.

[dougettinger]

So an interesting question comes to mind. If humans are living in one of these galaxies traveling faster than the "c"; and since velocity has direction, then observers in these galaxies would only see other galaxies only in one direction or a 180 degree hemisphere. And as this galaxy went faster and faster, an observer would eventually only be able to see galaxies directly ahead in the path of travel. Is this thought experiment correct ?

I don't think so. Think of it this way: our Milky Way galaxy is moving through its local space at a speed which is only a tiny fraction of c, yet it is separating from galaxies outside our observable Universe at c or even faster. "Separating" due to the expansion of space is not the same as "velocity" in the sense you're describing.

Rob

So the velocity of separation of space and the velocity of things within a certain frame of reference are different. Our observable universe is one huge frame of reference where anything with respect to another thing cannot go faster than the speed of light. It makes sense to me.

Particles being created soon after the Big Bang could easily go faster than the speed of light with respect to the proposed singularity point, but once photons were created then the speed of light became the communication between particles. But why do the particles cease accelerating and slow to the velocities we see today ?

And how do astronomers measure the velocity of galaxies? What frame of reference is used?

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

So the velocity of separation of space and the velocity of things within a certain frame of reference are different. Our observable universe is one huge frame of reference where anything with respect to another thing cannot go faster than the speed of light.

Not quite. Our location defines a (not "the") frame of reference for the observable Universe that we find convenient for many purposes. There is no single frame of reference for the observable Universe- each point in it (and in the Universe as a whole) defines its own frame. Things in the observable Universe can go faster than the speed of light with respect to each other. But those things would be outside of visibility to each other, though not to us. That is, they might be within our observable Universe but not each others'.

Particles being created soon after the Big Bang could easily go faster than the speed of light with respect to the proposed singularity point, but once photons were created then the speed of light became the communication between particles. But why do the particles cease accelerating and slow to the velocities we see today ?

First, there is no "proposed singularity point", so you can't think of that as defining a reference frame. Second, remember that the speed of light isn't a physically useful concept. What matters is the universal constant c. It happens that c defines the maximum speed of a photon, but that's all. Before there were photons, c still existed (although it may not always have had the same value). Presumably, nothing ever went faster than c, meaning no information was ever transmitted faster than that. Particles haven't slowed down (or more precisely, some are faster and some are slower, depending on the forces that have acted on them) as the Universe aged. The evidence suggests that the Universe itself has not grown at a uniform rate.

And how do astronomers measure the velocity of galaxies? What frame of reference is used?

Normally, the velocity of everything we observe in the Universe is measured with respect to our own frame of reference. That is, we assume we are not moving. In some cases that frame may be adjusted for local motion that we understand physically: our orbit around the Sun, the Sun's orbit within the Milky Way, possibly the motion of the Milky Way in the Local Group.

It is a little tricky figuring out what the velocity of a galaxy really is. Most galaxies are at cosmological distances, meaning they exhibit significant cosmological redshift. That is often interpreted as a velocity, analogous to Doppler redshift, but really it is something different. Within a galaxy cluster, relative velocities can be measured using differences in redshift, but overall, there's really no way to tell how fast a galaxy is moving away or towards us, with respect to the region of space it is in.

[dougettinger]

I am gaining much more clarification about cosmoslogy. Thank you.

If a distant galaxy is measured as having one of the highest red shifts it means that the separation velocity is close to the velocity of light. However, if out galaxy is moving away in the opposite direction, then its own velocity should be substantially less. I hope my thinking is now correct.

If a photon leaves a spotlight in the same direction as it is traveling at half of "c" then why does not this photon go at 1 1/2 times "c"?

If a photon considered to be a massless particle or a wave, but nevertheless a particle, leaves a flashlight at the velocity of "c" (assuming a vaccum) why doesn't this particle have to accelerate first to achieve its maximum velocity ? My thought is that everything is expanding uniformly at the velocity of "c" - not just galaxies.

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

If a distant galaxy is measured as having one of the highest red shifts it means that the separation velocity is close to the velocity of light. However, if out galaxy is moving away in the opposite direction, then its own velocity should be substantially less. I hope my thinking is now correct.

Sort of. There is some natural confusion about what cosmological redshift actually means. It isn't the same as Doppler redshift. While the latter is the direct result of a recessional velocity, the former is the result of the expansion of the space the redshifted photon was traveling through during its trip from source to receiver.

What does it mean that "our galaxy is moving away in the opposite direction"? Again, velocity is relative. In our frame of reference, we are stationary and the distant galaxy is receding. In its frame of reference, we are moving. In some different frame, both are moving.

If a photon leaves a spotlight in the same direction as it is traveling at half of "c" then why does not this photon go at 1 1/2 times "c"?

This is fundamental to Special Relativity: a photon is always observed to have a velocity of c, regardless of the frame it is observed from. I don't know of any way to say "why" that is; it's just the way nature works.

If a photon considered to be a massless particle or a wave, but nevertheless a particle, leaves a flashlight at the velocity of "c" (assuming a vaccum) why doesn't this particle have to accelerate first to achieve its maximum velocity ?

This assumes that a photon can be at rest. It can't. (Nor is a photon massless.) A photon comes into existence with a velocity of c. Again, this is just the way nature works. Photons and other quantum particles behave differently than macroscopic objects. The rules are different.

My thought is that everything is expanding uniformly at the velocity of "c" - not just galaxies.

I don't really understand what you mean by that, but by any reasonable way I can interpret it, I'd say it's false.

[dougettinger]

I will ask a question to expose my last thought. Galaxies are receding/separating and/or space is expanding. Why don't stars recede from each other in a similar fashion because these stars reside in the same expanding space ?

Doug Ettinger

[Chris Peterson]

I will ask a question to expose my last thought. Galaxies are receding/separating and/or space is expanding. Why don't stars recede from each other in a similar fashion because these stars reside in the same expanding space ?

This is fundamental to GR. Space is held together by gravitational attraction. It is empty space that is expanding, not regions with strong gravitational fields.

[dougettinger]

Yes, that is a good simple answer. Lets compare the ratios of solar masses and light year distances for the Sun and its closest star, and the Milky Way Galaxy and its nearest large galaxy.

1 M / 4 ly = .25 verses 7.1 x 10(11) M / 2.5 x 10(6) ly = 2.8 x 10(5)

Indeed, there is quite a difference. So with clusters of galaxies there is still enough gravitational attraction to hold them together. In fact, I presume that Andromeda is moving toward the Milky Way due to gravitational attraction. In summary, Dark Energy is being opposed by the gravitational attraction of regular matter and Dark Matter. However, the expanding universe leads us to believe that Dark Energy is the more powerful entity.

I found your quote very intriguing. "A photon comes into existence with the velocity of "c". I just like to think outside the box when it strikes me. Just suppose all matter is expanding as witnessed by the galaxies. Inertia was supplied by the Big Bang to accelerate all particles radially outward. The present average velocity in our region is now "c". We can only notice this expansion due to acceleration of matter over very large expanses of separation such as the distance between galaxies. The distance changes between stars and planets is just too small to measure over mankind's span of time. And the velocity change measured in angstroms is too small to measure. Hence, it appears that no velocity change occurs, but this is why photons leave an object at the present speed of "c" without accelerating. All matter is expanding uniformly at the velocity of "c" throughout space. Different velocities can occur within this universal frame of reference as is witnessed by a growing animal cell, a moving car, or an orbiting planet. These velocities are so minute that there is no affect on the overall extremely large velocity of "c". Different velocities occurred because of discontinuties when energy was converted to mass via E = mc(2).

Perhaps the inertia of expansion of concentrated matter produces what we identify as gravity.

Please have patience with this drabble. Maybe you can shoot a hole in this thought experiment.

Doug Ettinger
01/11/2011

[rstevenson]

... Just suppose all matter is expanding as witnessed by the galaxies.

As Chris mentioned above, matter is not expanding; space is -- in particular it appears the extremely empty parts of space that make up the bubbles between the clusters and super-clusters of galaxies may be where the expansion is mostly taking place.

... Inertia was supplied by the Big Bang to accelerate all particles radially outward.

Particles that existed early in the universe were not accelerated by inertia supplied by the big bang; the space they were in expanded while the particles did whatever they needed to do -- that is, they would have remained in a state of rest or uniform motion unless acted upon by a force. (And the big bang is not, in that sense, a force.) As well, the concept of "radially outward" isn't going to work, as it implies an omnipotent viewpoint, as well as a center from which everything expanded.

It's hard to talk about this subject without using either Math or a metaphorical illustration. Not being competent to use the former (yet) I'll try the latter. I'll use the classic surface-of-a-balloon metaphor. Imagine beings on the surface of an expanding balloon. They can't get off the balloon because there is no "off" into which to get in their universe. They also can't get into or even see into the balloon, for the same reason. In fact, they have no concept of being on a 3D object at all; their universe is strictly 2D, being the surface of the sphere. As the balloon expands a being at one point on the surface sees all other points moving away from it. It does not see them moving outward from a central point, though we can easily see that happening from our omnipotent viewpoint. Similarly, we in our 3D universe can only see other points in our universe getting further away; we cannot see them moving radially out from the "center" of our 4D space-time continuem, just as we cannot see our universe expanding within something outside of itself.

Rob

[Chris Peterson]

I found your quote very intriguing. "A photon comes into existence with the velocity of "c". I just like to think outside the box when it strikes me. Just suppose all matter is expanding as witnessed by the galaxies. Inertia was supplied by the Big Bang to accelerate all particles radially outward. The present average velocity in our region is now "c". We can only notice this expansion due to acceleration of matter over very large expanses of separation such as the distance between galaxies. The distance changes between stars and planets is just too small to measure over mankind's span of time. And the velocity change measured in angstroms is too small to measure. Hence, it appears that no velocity change occurs, but this is why photons leave an object at the present speed of "c" without accelerating. All matter is expanding uniformly at the velocity of "c" throughout space. Different velocities can occur within this universal frame of reference as is witnessed by a growing animal cell, a moving car, or an orbiting planet. These velocities are so minute that there is no affect on the overall extremely large velocity of "c". Different velocities occurred because of discontinuties when energy was converted to mass via E = mc(2).

Perhaps the inertia of expansion of concentrated matter produces what we identify as gravity.

Please have patience with this drabble. Maybe you can shoot a hole in this thought experiment.

I don't understand your thought experiment well enough to shoot.

Note, however, that the idea of "inertia" probably doesn't apply to the expansion of space. Matter itself was not propelled anywhere by the Big Bang. And I don't know what it means to say that matter is expanding uniformly at any speed. Speed is relative; it must be measured with respect to something, and it is a matter of simple observation to determine that there is no uniform motion of matter, since if that were the case, we'd not observe any motion at all.

[dougettinger]

Thanks for the reply. You do bring forth another question. You state that matter itself was not propelled anywhere by the Big Bang. I always thought that during the epoch when enough cooling occurred that plasma was formed and then finally atoms. Would not these atoms be mattter that is being propelled outwardly in all directions ? Maybe I really do not understand the Big Bang.

Returning to my idea: You stated that if there is uniform motion of matter then no motion would be observed at all. In local space that would be correct. However, observing the galaxy redshift could be proof of this uniform motion because of the large expanses of time and distance. Just say that the Earth, Sun and other solar system bodies are expanding at "c" as well as their spatial distances, then we as humans would not observe this motion. But since matter has conglomerated over the eons, the relative motions between conglomerations can be observed by mankind because of the much smaller relative velocities. And this would, of course, apply to moving conglomerations of matter on the surface of Earth.

Can several different frames of motion be represented mathematically inside multiple overall encompassing frames of reference ? Venn diagramming might apply, but I do not know this. I am simply trying to explain for myself why light might come into existence at the velocity of "c" in our "neck of the woods". It might help explain Dark Energy, too.

Doug Ettinger
01/12/2011

[The Code]

Can several different frames of motion be represented mathematically inside multiple overall encompassing frames of reference ? Venn diagramming might apply, but I do not know this. I am simply trying to explain for myself why light might come into existence at the velocity of "c" in our "neck of the woods". It might help explain Dark Energy, too.

186 thousand miles per second, "c" is universal, not our "neck of the woods" How would it explain Dark Energy?

Explaining why Light Speed "c" is set at 186 thousand miles per second, is another story. Yet untold. Huh?
It does not Matter how many times you over lay, or take away, The Speed of light remains the same.

tc

[dougettinger]

I am not questioning that the speed of light remains the same and is proven by many well designed experiments. But no one yet knows if the speed of light is different beyond our "observable" universe. We can only think of such velocities. The "neck of the woods" I refer to is the "observable" universe. Dark Energy is needed to explain the expanding universe. I am just performing a "thought experiment". If the speed of light was accelerating by only a few angstrom units per year, it could not be detected within the limits of error of experiments that have been performed to date. But the thought of it accelerating could be a possible answer for Dark Energy. Again as I have already mentioned, I am trying to answer for myself why a photon comes into existence at the velocity of "c". It is usually dismissed at being the way of nature.

It is your choice to participate or not participate in this "thought experiment". I try to remain humble and bow to any dogma found in current science, But, of course, my brain keeps working.

Doug Ettinger
Pittsbugh, PA

[Chris Peterson]

I am not questioning that the speed of light remains the same and is proven by many well designed experiments. But no one yet knows if the speed of light is different beyond our "observable" universe.

There is nothing special about the observable Universe. It is simply a region of the Universe defined by expansion: anything outside it has simple reached a velocity greater than c with respect to us, and is therefore not capable of interacting with us anymore. Every point in the Universe has its own such observable sphere. There seems to be no reason to think that ours is somehow special, and that physical laws (or constants) are different outside it.

Dark Energy is needed to explain the expanding universe.

You are misunderstanding dark energy. It is not required to explain the expansion of the Universe. That was understood for a long time without any need to invoke dark energy. What changed was that there was a new observation: the rate the Universe is expanding is not constant or slowing, as expected, but is speeding up. It is that speeding up that requires dark energy, or something that behaves like it. Of course, it is still possible (although increasingly less likely) that the observation of increasing expansion rate is incorrect. But since dark energy fills in other holes in earlier theory, it is probably here to stay.

Again as I have already mentioned, I am trying to answer for myself why a photon comes into existence at the velocity of "c". It is usually dismissed at being the way of nature.

Ask yourself why a photon should not do this. It's an equally valid question.

[Céline Richard]

Dark energy is not required to explain the expansion of the Universe. That was understood for a long time without any need to invoke dark energy. What changed was that there was a new observation: the rate the Universe is expanding is not constant or slowing, as expected, but is speeding up. It is that speeding up that requires dark energy, or something that behaves like it.

So the rate the Universe is speeding up... How can it be possible: is it the consequence of any theory, or is it just an observation we still don't know how to explain? Is it new for the Universe, or has the Universe always been expanding while speeding up?
Do scientist have any idea about where do black energy come from ?

Céline

[Chris Peterson]

So the rate the Universe is speeding up...

The rate of expansion of the Universe is speeding up.

How can it be possible: is it the consequence of any theory, or is it just an observation we still don't know how to explain? Is it new for the Universe, or has the Universe always been expanding while speeding up?

The apparent increase in expansion rate is an observation. With that observation came the need to provide an explanation, which dark energy does. In addition, dark energy fits into other parts of cosmological theory, as well. The expansion history of the Universe is complex, as it behaved curiously at the very beginning. The actual rate of expansion is determined by different things: the "inertia" of the original expansion and the inflationary expansion, gravitational attraction, dark energy repulsion, and maybe more. I believe that the most popular current viewpoint is that after the inflationary period, the rate of expansion was decreasing, because gravity dominated dark energy. But once the Universe became sufficiently large, dark energy became the dominant "force", and the rate of expansion began to increase- a trend that will presumably continue forever.

Do scientist have any idea about where do black energy come from ?

It is a property of the Universe. It may not be meaningful to ask where it came from (or at least, no scientific answer may be possible).

[Céline Richard]

I believe that the most popular current viewpoint is that after the inflationary period, the rate of expansion was decreasing, because gravity dominated dark energy. But once the Universe became sufficiently large, dark energy became the dominant "force", and the rate of expansion began to increase- a trend that will presumably continue forever.

That's very interesting.

Do scientist have any idea about where do black energy come from ?

It is a property of the Universe. It may not be meaningful to ask where it came from (or at least, no scientific answer may be possible).

Yes, it is a property of the Universe. I am sorry to have expressed myself in a confuse way. To express better what i mean, maybe it would be good to make a comparison. A force happens because there is gravitation (involving bodies with different masses), or magnetism (involving electrically charged particles), for example. When a force occurs thanks to black energy, my new question is: does it mean black energy is like a fundamental interaction? Or is it more something, a kind of "body"? If it is like a fundamental interaction, maybe black energy could be related to a new theory, in the future. If it is just something, a kind of "body", perhaps we could seek how it has formed in the Universe (by wondering if it is a basic component, like atoms, or not, for example).

Céline

[dougettinger]

Thanks for the reply. You do bring forth another question. You state that matter itself was not propelled anywhere by the Big Bang. I always thought that during the epoch when enough cooling occurred that plasma was formed and then finally atoms. Would not these atoms be mattter that is being propelled outwardly in all directions ? Maybe I really do not understand the Big Bang.

I am anxiously awaiting some hopefully easy answer to the above question which has not arrrived yet. Perhaps Chris Peterson could answer this concern. Thanks.

Yes, you are correct. Dark Energy is required to address the increasing rate of expansion of interglaxalar space. And if photons or their velocity "c" is accelerating by a very small undectable amount ever since the inflationary period of the Big Bang then there would be a reason for the increasing rate of expansion of space.

Regarding a photon beginning its existence at the velocity of "c": I have a difficult time envisioning anything that does not start at rest when it is created unless it is starting from a moving object. I need some help making the jump from Newtonian to Quantum Mechanics.

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

Thanks for the reply. You do bring forth another question. You state that matter itself was not propelled anywhere by the Big Bang. I always thought that during the epoch when enough cooling occurred that plasma was formed and then finally atoms. Would not these atoms be mattter that is being propelled outwardly in all directions ? Maybe I really do not understand the Big Bang.

I am anxiously awaiting some hopefully easy answer to the above question which has not arrrived yet. Perhaps Chris Peterson could answer this concern. Thanks.

Let's go back to the balloon analogy. The universe is the surface of the balloon, so this is a 2D universe we are considering. You can stick little dots all over the surface to represent galaxies. As the balloon expands, these galaxies are getting farther apart. But are they moving? You could argue that they are not. If you were perched on one of those dots, you'd feel no forces in the plane of your universe. No acceleration, even if the expansion rate was not uniform. Of course, from our vantage point we understand that you'd feel a force in what we'd call the vertical or radial direction... but that direction isn't accessible to those living on the balloon, because they only perceive two dimensions. And if you look at what direction the dots are actually traveling, it isn't a direction along the surface, but is in a straight line away from the center of the balloon- a point that isn't even in that spatial universe.

Now, if you can, extend the analogy to our own Universe. We inhabit the 3D surface of a 4D universe. Distant objects aren't really moving with respect to each other (except in a minor, non-cosmological way). What's happening is that the Universe is expanding, and all these essentially stationary objects are staying in place. The only direction anything is moving is away from the 4D center of the Universe- the point where t=0. We are moving on the radial (time) axis of the Universe. We don't feel any forces on this axis. We can't see along this axis ("outward", the direction we are expanding, is the future; "inward", the direction we came from, is the past).

So, from the instant of the Big Bang to now, nothing is moving very much, nothing was propelled, nothing felt any forces from the BB.

[owlice]

Chris, great explanation; thank you.

[rstevenson]

Yes, much more complete than mine. I'll try to remember the balloon analogy that way.

Rob