If the Universe is Expanding...

reply to post by CLPrime

Some of the physics you mention is actually a bit off, but your point is valid. In fact, I'm inclined to agree with your conclusion.

Why thank you, I was expecting more criticism. Actually I am interested in reading why you think my physics are off. I do like to learn when it comes to physics and astronomy.

Originally posted by smithjustinb
Maybe it is expanding at the same rate locally, but non-locally we are able to observe the expansion because it is expanding at a faster rate then the rate we expand. Thus my theory remains in tact just altered.

If the Universe is expanding at a constant rate everywhere (ubiquitous) then I think that we would be unable to determine this supposed expansion. If, however, there are differing levels of expansion (local and non-local areas) then this would indicate other outside forces altering the universal rate of expansion. At this point we should focus on these other forces and forget the idea of a constant universal expansion since we would most likely be unable to measure that anyway.

I am following your idea and I think I understand the concept of universal expansion. This reminds me of a book I read some years ago detailing the idea of an atomic expansion which sounded plausible until it got to the point of space expanding as well. There is a fundamental problem when we label space as an absolute void and then determine that this void is expanding. It's synonymous to the equation 0x0=?.


reply to post by Arbitrageur

There's a ton of evdence for the hubble constant and while it appears to be relatively constant in space at an instant in time like the present, we also know that it's NOT constant over time,

Time and distance are relative, I feel you might be presenting an unknown value that arbitrarily adjusts the equation to get the desired results. Could you post some highlights of all this evidence of the Hubble being constant in a form that I might be able to understand? I know a red shift of light is measured from distant galaxies and this does indicate an acceleration as one possible explanation for this red shift. Can there be another reason for this observed red shift?

Now if I understand the rest of your reply I see that the Hubble constant is proven to not be constant? I would concur with this description yet why are we still using this as a constant? Clearly there exists a problem here.

reply to post by CLPrime

Exactly. Specifically, in a survey of several supernovae up to a redshift of z=1 (when the universe was about half its current size), it was found that these stars are further away than predicted by a uniformly expanding universe

So this is evidence against the universal expansion theory, correct? I see this as yet another discrepancy with the Hubble constant.

reply to post by CLPrime

The space between them is expanding, galaxies are not moving away from each other.

This is where I have a problem in understanding this theory. Define space. Is it an absolute void, empty and absent of all matter? Or is it a measurable medium full of matter and energy? We should not cherry pick here but rather define space as one or the other. To state that space as an absolute void devoid of all matter expands is beyond reason.

If we are measuring the amount of red shift of each galaxy how can we determine its distance using the same measurement that determines its acceleration? If the Hubble is a constant and can be relied on than I'm wrong in my assertions here. But if it is not a constant, as is indicated several times in the thread, how would we ever know? We are using an arbitrarily adjustable tool to try and measure an unknown. What is needed here is an independent way of measuring distance to either confirm or deny the supposed expansion of space. Even if we do determine that space itself is expanding then the question is what is the cause, certainly not some theorized long ago big bang.

reply to post by Maslo

I feel the need to ask, and I can't quite put this into proper perspective, but is dark energy and/or dark matter the same as the theory of a luminiferous Aether?

Originally posted by Devino
reply to post by Maslo

 

I feel the need to ask, and I can't quite put this into proper perspective, but is dark energy and/or dark matter the same as the theory of a luminiferous Aether?

No, it is not the same. Dark matter is simply matter that is transparent to lighť and other forces, except gravity. Dark energy is a force pushing all things apart proportionally to the distance. Luminiferous aether is a disproven concept of a medium for transmission of light waves. These are all separate ideas.

reply to post by Maslo
Correct, except I think the transparency to light part isn't entirely correct. Some scientists claim to have found the dark matter within galaxies and at least that matter may be baryonic meaning not transparent to light, if they're right. Some dark matter may be transparent to light but some dark matter isn't like MACHOS (Massive Compact Halo Objects), as astronomers call them:

www.spitzer.caltech.edu...

scientists use the term "dark matter" as an umbrella definition for all the material in the Universe that can't be seen. They believe that there are two components to dark matter. A large fraction of dark matter is made up of exotic materials, different from the ordinary particles that make up the familiar world around us. Meanwhile, some dark matter may consist of dark celestial bodies like brown dwarfs, which do not produce optical light and are too faint to visibly detect from Earth.

One guess on dark energy is that it's possibly related to vacuum energy and Einstein's cosmological constant in relativity, which basically says that vacuum space has a small amount of energy or pressure which pushes things apart, and we can calculate the exact amount of energy, but we don't really understand it, that's why we still call it dark.

And yeah, the idea of luminiferous aether is dead.

If the universe is expanding, then it is not a closed system, is it? therefore, is the second law of thermodynamics valid, which requires a closed system?

Originally posted by masterp
If the universe is expanding, then it is not a closed system, is it?

Unknown.
en.wikipedia.org...
Wikipedia calls it an "Isolated system" rather than a "closed system" and I suppose something that's expanding could be isolated if the isolated expanded state is compared to the pre-expanded isolated state. If the observations of "dark flow" indicate the transfer of matter from our universe to another universe, that would tend to confirm it's not an isolated system, but wikipedia claims that it is isolated, and that could possibly be correct, though I'd argue we aren't 100% sure about that:

According to the second law the entropy of any isolated system, such as the entire universe, never decreases

is the second law of thermodynamics valid, which requires a closed system?

George Box said, "all models are wrong, some are useful". I'm not sure how useful it is to try to apply the second law to the entire universe. We aren't sure how big the universe is, but we suspect the universe is larger than the observable universe, and since we can't see what's outside the observable universe, that's a matter of speculation.

So the question is really moot since there's no way to even observe what's outside the observable universe to see if the 2nd law applies in totality or not. Going back to Box's quote, it appears it's not very useful to worry about whether the 2nd law applies to the entire universe, if we can't observe the entire universe.

Originally posted by Devino
reply to post by CLPrime

 

Some of the physics you mention is actually a bit off, but your point is valid. In fact, I'm inclined to agree with your conclusion.

Why thank you, I was expecting more criticism. Actually I am interested in reading why you think my physics are off. I do like to learn when it comes to physics and astronomy.

You said...

For example we have ways of measuring the distance of objects in space to a certain point (parallax, Cepheid variables and light magnitudes of stellar clusters) which is not very far away cosmologically. From then on we use the Hubble "constant" to measure distance by the amount of speed this object is supposedly moving away from us at.

First of all, this might just be a matter of semantics, but objects are not "moving away from us" at any proper velocity. The space is expanding between us and those objects. This is a mistake made even by physicists (especially those not deeply versed in cosmology), but to say that redshift is a measure of an object's velocity is inaccurate. A small amount of redshift is due to the velocity of these objects - the rest is a measure of how much "space" (which I'll define later in this reply) has been stretched in the time the light from the object has been travelling. If the universe has expanded twice the size in the time the light travels from a galaxy to us, then that light will exhibit a redshift of z=1 (that is, twice the wavelength it was when it was emitted).

Also, you said that the last of the measuring techniques (light magnitudes of stellar clusters) doesn't extend very far away, cosmologically. In fact, this method accurately determines distances out to 75% of the radius of the observable universe (about 10 billion light-years). It is only beyond this that the Hubble "constant" is used.

reply to post by Arbitrageur

 

There's a ton of evdence for the hubble constant and while it appears to be relatively constant in space at an instant in time like the present, we also know that it's NOT constant over time,

Time and distance are relative, I feel you might be presenting an unknown value that arbitrarily adjusts the equation to get the desired results. Could you post some highlights of all this evidence of the Hubble being constant in a form that I might be able to understand? I know a red shift of light is measured from distant galaxies and this does indicate an acceleration as one possible explanation for this red shift. Can there be another reason for this observed red shift?

Now if I understand the rest of your reply I see that the Hubble constant is proven to not be constant? I would concur with this description yet why are we still using this as a constant? Clearly there exists a problem here.

The Hubble "constant" is most certainly not constant. By analyzing the magnitudes of supernovae out to a magnitude of z=1, we know that the expansion of the universe has been accelerating for the past 5 billion years. This means the Hubble "constant" has been increasing over the past 5 billion years.

reply to post by CLPrime

 

Exactly. Specifically, in a survey of several supernovae up to a redshift of z=1 (when the universe was about half its current size), it was found that these stars are further away than predicted by a uniformly expanding universe

So this is evidence against the universal expansion theory, correct? I see this as yet another discrepancy with the Hubble constant.

No, it's evidence that the expansion of the universe has been accelerating for 5 billion years. Remember, where seeing these supernovae as they were up to 5 billion years ago, but the light coming from them is (up to 25%) dimmer than it should be. This means they are further away than they should be, which means the expansion of the universe has been increasing since the light was emitted.

reply to post by CLPrime

 

The space between them is expanding, galaxies are not moving away from each other.

This is where I have a problem in understanding this theory. Define space. Is it an absolute void, empty and absent of all matter? Or is it a measurable medium full of matter and energy? We should not cherry pick here but rather define space as one or the other. To state that space as an absolute void devoid of all matter expands is beyond reason.

Finally, I will define "space". I typically try to avoid it, 'cause it's where cosmology and astrophysics melds with quantum mechanics, but, if I must...
Empty space (specifically, the "vacuum") is defined as being at the zero-point energy level. I don't know how much you know about quantum mechanics, but, even though it's called the "zero-point", it is far from empty. A vacuum is full of energy embodied by virtual particles, which "pop" in and out of existence (allowed by the Heisenberg Uncertainty Principle). "Zero-point" energy is merely the lowest energy state of region - it is NOT a region of zero energy (it is, however, a region void of matter).
Now, it is possible for a region at zero-point to spontaneously collapse to a lower energy level, releasing A LOT of energy in the process (what people typically call "free energy"), but, theoretically, this hasn't happened since the Inflation Epoch, almost 14 billion years ago. In fact, it's theorized that it was this massive release of energy through the collapse of the primordial zero-point vacuum that led to the early rapid inflation of the universe.

If any of that is unclear, or if you have any questions, feel free to ask. I just wanted to briefly address some things - I can certainly get deeper into things if you want.

So CLPrime, do you reside with the concept that the 'Big Bang' singularity was a point in space, or more like a point in time?

reply to post by Illustronic


Theoretically, I would say both. The "Big Bang" represents the creation of space-time, so it would have started as a momentary singularity of both time and space. Prior to the so-called Big Bang, neither time nor space existed.
The Big Bang, then, represents the creation of space and time, as well as its subsequent rapid inflation caused by the collapse of the initial zero-point vacuum.

reply to post by CLPrime


I rather suspected an answer like that but in at least my head, that answer is a bit evasive in describing the massive scale of distances theoretically observed in the time frame also theoretically postulated without, say for instance, light speed being exceeded in expansion (by mass) from a point in space to the distances observed today. That's where I have a problem with a point in location, and not just brushing away the idea of everything in one location by advancing the idea of space and time creation, and everything before is inconsequential.

I find the descriptions you summarized on what space is very interesting as a teaser, and I understand a little about the space between mass in particle physics but I just cannot wrap my head around everything compressed to a point of location observed today in that amount of finite space without creation from nothing along the expansion way. So to keep my head from exploding I view singularity as a point in time and not location in space. I think its rather presumptuous for us to say 13.8 (or whatever it is) light years away is the furthest we can see (in any direction) would by logic place our observation point in the Universe at the center. That's a rather Godly idea to propose, don't you think?

Or did the Hubble just happen to image the only correct point in space that just happens to be the furthest from us?

Somewhere in all of this Relativity has been violated.

BTW, I appreciate what you offer here to us novices, CLPrime.

[reply to post by Illustronic

I rather suspected an answer like that but in at least my head, that answer is a bit evasive in describing the massive scale of distances theoretically observed in the time frame also theoretically postulated without, say for instance, light speed being exceeded in expansion (by mass) from a point in space to the distances observed today. That's where I have a problem with a point in location, and not just brushing away the idea of everything in one location by advancing the idea of space and time creation, and everything before is inconsequential.

Alrighty...let's get down to some real physics.
Special Relativity, as you know, concludes that nothing with real mass at rest can have a velocity greater than the speed of light. However, this conclusion has a limit. Consider why no massive object can travel faster than the speed of light: as velocity increases, so does mass, which, in turn, increases the amount of force needed to accelerate that mass... and, at the speed of light, mass becomes infinite, requiring an infinite force to accelerate that mass to the speed of light, which, of course, is impossible. But, now, consider the expansion of the universe. Is the matter in the universe (galaxies, stars, whatever) really travelling with a true velocity (proper motion)? Short answer: nope. As far as expansion is concerned, no force is causing objects in the universe to move. It is space, itself, which is stretching. This stretching, then, can give distant objects an apparent velocity greater than the speed of light (actually, there's something interesting about this, which I'll get to in a sec), but the objects, themselves, are not being moved.
A decent (and well-known) illustration of this is two dots on a balloon. When you blow up the balloon, the dots move further away from each other, but neither dot is actually moving... if they were, their positions on the balloon would change. They do not. There is no proper motion - only apparent motion. Apparent motion can exceed the speed of light, but proper motion cannot.

Now, what's "interesting about this" is, sometimes, people will say, "The speed at which objects are moving away from us increases with distances, so that, beyond a certain distance, objects appear to be moving away faster than the speed of light." This is wrong. First of all, like I just said, the objects aren't really moving away from us - the space between us and the objects is stretching. Second, and the thing I really want to point out, the edge of the observable universe is the point where the apparent speed of those objects is almost equal to the speed of light. Nothing that we can see even appears to be moving away from us at faster than the speed of light. This should actually be obvious. If an object appears to be moving away at a velocity of or greater than the speed of light, then the light it emits will never reach us. At the edge of the observable universe, the apparent motion of the objects we see approaches, but never reaches, the speed of light.

I find the descriptions you summarized on what space is very interesting as a teaser, and I understand a little about the space between mass in particle physics but I just cannot wrap my head around everything compressed to a point of location observed today in that amount of finite space without creation from nothing along the expansion way. So to keep my head from exploding I view singularity as a point in time and not location in space. I think its rather presumptuous for us to say 13.8 (or whatever it is) light years away is the furthest we can see (in any direction) would by logic place our observation point in the Universe at the center. That's a rather Godly idea to propose, don't you think?

As I explained above, there is a reason that what we see is called the "observable universe." Objects beyond the edge of what we see have an apparent motion greater than the speed of light, so the light from them never reaches us and we never see them. What we see is not the whole universe... we only see our little sphere of it. You could be on one of those supernovae 10 billion light-years away and, if you were to look out in all direction, you would see the exact same expansion we see from Earth. This is another point that the balloon analogy helps to illustrate...
Let's say you had a balloon covered with equally-spaced dots, and you pick one of those dots to represent Earth. As you inflate the balloon, the dots closest to "Earth" are going to move away from Earth slowly, while dots further from Earth are going to move away faster. This is exactly what we see - objects close to us barely seem to move at all, while, at the edge of the observable universe, objects seem to be flying away from us at near the speed of light.
Now, what would happen if you picked another dot to represent Earth? The observation would be the same, wouldn't it? In the same way, no matter where you are in the universe, the expansion looks the same - it appears to increase with distance. And this is what the Hubble "constant" measures, the rate at which the expansion of the universe appears to increase with distance (currently measured at around 72 km/s for every million parsecs).

Also, no matter where you are in the universe, the furthest out you can (currently) see is about 13.75 billion light-years (the distance light can cover in the time since the universe formed - about 13.75 billion years). So, for an object 20 billion light-years away, the Earth is outside of its "observable universe" - they can't see us, and we can't see them.

Now, I want to cover the inflation (the early rapid expansion) of the universe a little more. You also mentioned the creation of matter out of nothing. This should answer that, as well.
I've already said that, according to the current theory, LCDM Cosmology, that sudden inflation was a result of the energy released by the collapse of the original zero-point vacuum. But, I never went into any detail. This is me going into detail...

Within the tiniest fraction of a second after the "singularity" formed, the simplest way to picture it might very well be as an empty ball - no matter, no energy. It was pure space-time with nothing occupying it. However, there's a funny thing about a quantum vacuum. Classically, a vacuum is void of all matter and energy. And, this is basically true in Quantum Mechanics, as well. But, in QM, a vacuum also hides a form of energy called zero-point energy (or, colloquially, "free energy"). To illustrate this, imagine standing on the ground. It's solid, and is effectively the lowest you can go. This is the quantum definition of a vacuum - it is the lowest energy level a region of space can obtain. But, now, back to you on the ground... suppose you're walking along, and, suddenly, you fall through into an old mineshaft. The ground had been the lowest you could go, but, now, you find yourself even lower. This can also happen with a vacuum. The zero-point energy can spontaneously collapse, falling to an even lower energy level and releasing energy (zero-point energy) in the process.
This is what cosmologists believe happened to trigger the early rapid inflation of the universe. The "singularity" was a vacuum having a high zero-point energy which spontaneously collapsed to a much lower level, releasing an immense amount of energy. This energy was what powered that period of inflation.
This also explain where matter came from. That energy "condensed" to form real particles, which, as the universe matured, became the matter we see today. And, over the past 13.75 billion years, that matter has gravitationally collected to form galaxies, stars, planets, and so on.

Now, the only question left to answer is where the "singularity" came from. What created it?

Fascinating, you just explained those video illustrations we all have seen and love, of this explosion and after the light from the blast (I know that the light was for illustration purposes only, because it took much longer for there to be light in the early Universe) but continuing on to the video, we suddenly start to see ourselves in the mist of sparkling lights a far as one can imaging growing coalescing into stars and then galaxies in very little time (again for illustration purposes). But now I have a better understanding of expanding space (at least) that for the time being will keep my head from exploding.

So thanks for that, you may have saved a life.

reply to post by Illustronic


Anytime.
Though, what I'm about to say may make your head explode anyway...

I said I agreed with your earlier conclusion, which was...

If you were to ask me... The big bang never happened, the Universe is not expanding as we think it is (I favor a more static like Universe-to put is simply), the Universe is far bigger and older than cosmologists believe it to be. We have A LOT yet to learn and I find it completely preposterous for anyone to have the audacity to give the Universe an age given how little we do know.

I'm currently on the fence, concerning an expanding versus static universe. I like two very different theories, and I'm not sure which one has the upper-hand.

The first isn't a formalized theory, it's more of a local hypothesis (and, by "local", I mean local to ATS). I can't remember who at the moment, but one member here believes that solar systems, galaxies, etc., are surrounding by something akin to a bubble, which leads to a lensing effect. This lensing redshifts light being emitted from the system inside it. In addition to this, it also redshifts light that happens to pass through it from other systems, causing light to exhibit a greater redshift at greater distances. This, then, leads to the redshifting we see, as well as the linear increase we see in that redshifting with distance, without the need of an expanding universe.

On the other hand (and this is the part that might explode your head), the second is a formal theory in astrophysics known as Scalar-Tensor-Vector Gravity (STVG). While the rest of astrophysics is looking for the existence of dark matter, its effects are just as readily described by a simple tweaking of General Relativity. This "tweak" of GR is STVG. Unfortunately, "simple" isn't quite as simple as it might sound.
In General Relativity, Einstein's field equations, which are used to calculate the gravitational field strength and its effects on space-time, come from something called the Einstein-Hilbert Lagrangian, which is a measure of the energy dynamics of the universe (embodied by gravity). Gravity, along with the 3 other fundamental forces, are called vector fields - that is, they are fields that exert a directional force within a given region.
Now, we all "know" that there are 4 fundamental forces, corresponding to 4 distinct vector fields.... but, STVG introduces a fifth vector field, represented by the Maxwell-Proca Lagrangian (you can find this all on Wikipedia, if you'd like - just look up STVG. That's actually why I'm going over all of this... the last time I mentioned STVG, the person looked it up on Wikipedia, saw all the math, and ran away). Interestingly enough, STVG also "promotes" the Gravitational constant, and two other constants, to the status of scalar fields (a field that assigns a magnitude to every point in space, but no direction... sorta like a force that doesn't really do anything). This introduces a third Lagrangian, defining the dynamics of those scalar fields. There's also a fourth Lagrangian, which defines the energy dynamics of the matter contained within the universe.
Now, finally, when you put this all together, you get a somewhat more complex picture of the universe, but, interestingly enough, a much more accurate one. And, the "simple" part of all this is that, in reality, all STVG has done is introduce a fifth force - the fifth vector field. But what effect does that fifth force have, you ask?
If you do the math (go ahead...I'll wait ), you find that STVG actually predicts that gravity is only Newtonian within, say, the size of the solar system, because this is the scale at which the fifth force acts. This force is repulsive, and it counteracts gravity at relatively small scales. Once you get beyond solar-system size, however, the fifth vector field becomes a background anomaly, and gravity becomes stronger than both Newtonian physics and standard General Relativity predict. This accounts perfectly for all observations that have necessitated the theory of dark matter (so, it makes dark matter obsolete), and it also explains why the expansion of the universe appears to be "recently" accelerating, as well as several other cosmological anomalies.

You can probably tell, I have a personal bias towards STVG, and not so much for the first static universe/bubble solar system theory, but that doesn't help me decide which is more likely to be right. Hmm...maybe you can decide for me. Which do you prefer?

reply to post by CLPrime


LOL CLPrime, I am a terminal Right Brainer and cannot possibly be of any mathematical assistance. I'll reside with the comfort of knowing somehow in the matter/antimatter conflict that it was matter that ultimately calculated to a number greater than zero.

Maybe a bit off-topic but while adding ingredients to a tossed salad last night, (carrots, celery, green onions, orange supremes and apple slices–green peppers, tomato slices, hot yellow pepper rings on the side for me), with lots of green leaf lettuce, in fact the whole head, I exclaimed to my wife that a salad should include a primary abundance of lettuce, otherwise I would not have ordered a salad to begin with, I'd have ordered something else.

The very imbalance from zero allows us to converse.

So finding the forces of nature that 'work' in the micro as well as the macro we always have this unknown 'exotic' force of undetermined origin, that in with the very same subatomic particles allows our salad to be much more than just lettuce, (but intentionally mostly lettuce), as well as carbon briquette grilled steak, and fermented berries.

So you see I was not entirely honest before, I don't believe I use the left side of my brain enough to equalize a construct of zero, thus, annihilation and balance of the matter/antimatter equation, could not occur in MY head.

In conclusion, have yourself a nice salad today CLPrime! At least knowingly one can at least approach a greater balance of diet.

(OK Illustronic now set down that glass of wine and fix that friggin dryer or something constructive!) The dryer checks out, I'm simply not getting enough voltage to power the heating element.

Excuse me for wasting your time with a rant, I'm feeling a little bit 'chippy' today. Apologies.

Originally posted by miniatus
I think it just means the space within the universe is expanding.. not the objects within the space.. just space itself.. A lot of scientists think of the universe not as infinite but as a bubble, and so imagine the bubble as getting larger, not the molecules inside the bubble.

Not expanding in a 3 dimensional sense. The Universe (according to Einstein) has 4 geometrical dimensions. (That's right 4 geometrical dimensions not time as the 4th dimension) The expansion is 4 dimensional and the shape of the universe is a 4th dimensional bubble. This mean that If you travel in a 3D linear direction in a straight line you will eventually return to the point of origin.

With a 4 dimensional expansion it also follows that the 3d dimension space also becomes larger. I.E the distance to circumnavigate the 4th dimension universe becomes longer.

I have my doubts about the validity of the big bang theory but that is another discussion.

reply to post by smithjustinb


We can observe galaxies that are, according to our current scientific understanding, about 13 billion light years away.

I have a problem with this. If the universe was created a little more than 13 billion years ago there would be no 13 billion year trajectory for that light to travel the distance if the universe is expanding from a singularity that arose just a few million years prior.

Lets move back lets say about 6 billion years.
The object we observe must according to current theory be a lot closer at that time but that leave us with another problem which is that the light from the object that reaches us now if it has travelled 13 billion years to reach us the object itself must currently be much farther away than the expected 13 billion years if following a constant or accelerating speed.


The universe must at some distant past have expanded well in excess of the speed of light for all this to add up, which of cause raises a whole new set of paradoxes.

Originally posted by Clavicula
reply to post by smithjustinb

 

The universe must at some distant past have expanded well in excess of the speed of light for all this to add up, which of cause raises a whole new set of paradoxes.

Nope, no paradox. Read this post of mine... the first half of it. The universe is free to expand as fast as it wants without violating any speed limits.

Originally posted by Clavicula

The Universe (according to Einstein) has 4 geometrical dimensions. (That's right 4 geometrical dimensions not time as the 4th dimension) The expansion is 4 dimensional and the shape of the universe is a 4th dimensional bubble. This mean that If you travel in a 3D linear direction in a straight line you will eventually return to the point of origin.

Not even a little bit. Einstein said nothing of the universe having 4 geometric dimensions... his physics is based entire in a 4-dimensional space-time having 3 spatial dimension and 1 temporal dimension. The only place higher dimensions come into play is in string theory, and these are baseless mathematical artifacts.
Cosmology does consider something akin to a 4th dimension, but your thinking seems to be somewhat out-dated. There is no current theory claiming that, if you keep going in any direction, you will eventually return to where you started. This was one of several possible geometries of the universe back in the 90s, called a "closed universe." The other possibilities were a "flat universe" and an "open universe". The current evidence shows that the universe is a "flat" 3-dimensional generally-Euclidean space (though, locally, within gravitational fields, space is curved/Riemannian) - it does not curve back on itself either spherically ("closed", as you appear to be describing) or hyperbolically ("open").

reply to post by Illustronic


Hmm...I seem to be both right- and left-brained. I guess that's why I love salad.
Now I'm hungry.

reply to post by Clavicula


13.75 billion years ago is different than just 13 billion years ago. That .75 billion years is more than enough time for matter to form and thus early 1st generation stars, and the collection into early chaotic galaxies by gravity (and that exotic force(s)).

It also allows the photons of light to reach us well before the space expansion accelerated to the degree it is now. Thus, that galaxy 13 billion lys away is actually much further away now, its photons got a head start so to speak.