Where is the edge of the universe

[Randomtask94]

I'm currently taking an Astronomy class (I'm a high school senior so it's not a very in-depth class) and this question comes up a lot. After thinking about the "edge of the universe" for a while, I came to a conclusion and "answer" that makes logical sense to me (although my teacher seems confused when I try to explain it to him). I personally don't understand the confusion but I will share my view on the "edge" problem... Again I'm no Physicist so please don't assume that I'm giving (or trying to give) the "correct" answer. The "correct answer" I feel could never really be found (at least not for many lifetimes) due to the distance and speed one would have to travel to find (or not find) an "edge". Anywho, here it goes;

Imagine a central point in the middle of a piece of paper. The piece of paper representing all of spacetime and this "central point" will be the "singularity" that is the big bang before expansion. At the point of expansion (the expansion of the matter and energy inside of the singularity), the matter and energy will begin to move across spacetime (time starts here) and keep moving forever or until the expansion rate slows enough for gravity to bring it all back in on itself. Now, you draw a circle (doesn't necessarily matter how large or small because this is purely a visual to make sense of it) around the "central point". This circle represents the current expansion in age and in space (how far the expansion has moved across spacetime). Outside of that circle is the future and therefore we can only reach it when the expansion has reached it. You cannot "go over" that "edge" unless you go into the future. I personally think that the Science-Fiction idea of "jumping into the future (or the past)" is silly, but that is debatable and isn't the point of my example so I digress. As far as the present goes, what is on the other side of the "edge" (besides the future) doesn't matter because you will never reach it outside of waiting until the future is here. Unless you could go faster than the expansion rate and faster than light, but that just isn't possible... as far as we know any who, but I like to think that Einstein was correct. If you try to vision an "edge" that is purely physical (does not include time in the "spacetime"), you will find yourself confused and frustrated trying to understand it. This is because the other side of that edge must be "nothing" otherwise it would be included in the "universe", and "nothing" doesn't make sense to current-human logic. For this reason, I find that one should include the "time" in "spacetime" to make more sense of it. Of course, there are multiple ways to think about the "edge" problem so, just accept the one that makes the most sense to you (even if someone claims that it "makes no sense" or is "wrong").

If I did not make myself clear, feel free to ask questions. Again, this is just my thought on the whole shibang so don't quote me as claiming to have the perfect answer or any of that jazz... I am not a Physicist, and I like to think that I'm not that arrogant.

 

[mfb]

but I like to think that Einstein was correct.

I don't think your model is possible in General Relativity.

 

[MathJakob]

Just throwing this out there, but is it not logical to think that the big bang would have projected matter out in all directions? Creating a 360 degree universe? Also is it not logical to think that the universe is a sphere but it's just so so big that even with our most poweful telescopes we can not see the horizon... Because the universe is expanding faster than the speed of light, light can not make a full circle and come back to us.

If the universe was not expanding, eventually light would complete a full circle. I think the curve is just so small and the universe is expanding faster than the speed of light so we can never see the horizon. It's just getting further away with every passing second.

 

[Boy@n]

I think the curve is just so small and the universe is expanding faster than the speed of light so we can never see the horizon. It's just getting further away with every passing second.

Others more knowledgeable can answer this well. I'd just like to say that if expansion stops all light will eventually reach us (later than sooner I guess) and (future) we might see birth of Universe :-)

 

[phinds]

Just throwing this out there, but is it not logical to think that the big bang would have projected matter out in all directions? Creating a 360 degree universe? Also is it not logical to think that the universe is a sphere but it's just so so big that even with our most poweful telescopes we can not see the horizon... Because the universe is expanding faster than the speed of light, light can not make a full circle and come back to us.

You apparently believe that the big bang happened at a point. That is the first misconception that is thrown out in cosmology 101. I suggest you read some actual cosmology before you start postulating things that don't make sense.

 

[phinds]

Others more knowledgeable can answer this well. I'd just like to say that if expansion stops all light will eventually reach us (later than sooner I guess) and (future) we might see birth of Universe :-)

We ALREADY see as far back as we are ever going to see in the visible spectrum. Google "surface of last scattering".

 

[julcab12]

Imagine a central point in the middle of a piece of paper. The piece of paper representing all of spacetime and this "central point" will be the "singularity" that is the big bang before expansion. At the point of expansion (the expansion of the matter and energy inside of the singularity), .

To get a better picture. I would suggest that you crumple the paper(spacetime) instead of having a dot and compressed it as much as possible until you create a condensed ball of paper of some sort. What you have now is a GUP but before that. Imagine that weird condensed ball appear from 'something'.(Quantum Fluctuation). We move 2 step forward. That ball of condensed paper rapidly inflate and after that at some point gradually expands.

We can't identify any edge since we only have the paper as everything so far(not some paper within a given space/room/table and so on, etc).^^

 

[Adrian07]

I have been contemplating the expanding universe theory with regard to the edge of the universe. As far as I am aware this theory resulted in the fact that if all motion in the universe was reversed then all would come together at a single point somewhere, which at that time would have been the whole universe.
If all started at a single point, and assuming time is imagonary i.e. just the rate of change, then the edge would now be 13.7blys away from that point. Using a simple diagram you can see that the oldest part of the universe would be at the center with age reducing as you move outwards. There are 2 problems with this picture 1 unless viewed from the center the universe would appear lop-sided regarding the age of what is seen 2 the furthest you could see would be half the age of the universe in light years. This picture puts everything inside an expanding circle looking towards the edge. This is what we appear to see but we do not see a lop-sided universe and we can see further than 7blys.
If time is real, being discussed in another thread, then a universe expanding in time and space should produce something closer to what we actually see, the universe would look the same in all directions and we would be able to see almost to the beginning, but would put us on the edge of the circle looking in which would put the edge of the universe not in space but just in front of us in time, strange as that might sound.
Of course if what I have read regarding the expansion of the universe from its beginning is incorrect then I will have to think again.

 

[skydivephil]

I think it is possible to see the birth of the unvierse in the futre, but it won't be via light or by the universe's expansion for the reason phinds pointed out. But there are two types of radiation that can penetrate the surface of last scattering.
1 neutrinos , these could take us back to about 2 seconds after the big bang.
2 gravity waves, these could go even earlier and some have suggested even before the big bang itself.

The technology needed for this is not going to happen in the next fw years in my opiion, it's somewhat scifi but it is not impossible.

 

[phinds]

I have been contemplating the expanding universe theory with regard to the edge of the universe. As far as I am aware this theory resulted in the fact that if all motion in the universe was reversed then all would come together at a single point somewhere, which at that time would have been the whole universe.

As I believe has been pointed out to you in other threads, this is complete nonsense and is most emphatically NOT believed by any serious cosmologist.

 

[phinds]

To get a better picture. I would suggest that you crumple the paper(spacetime) instead of having a dot and compressed it as much as possible until you create a condensed ball of paper of some sort. What you have now is a GUP but before that. Imagine that weird condensed ball appear from 'something'.(Quantum Fluctuation). We move 2 step forward. That ball of condensed paper rapidly inflate and after that at some point gradually expands.

We can't identify any edge since we only have the paper as everything so far(not some paper within a given space/room/table and so on, etc).^^

AAARRRRRHHHH ... I understand what you are saying and I am NOT saying it is wrong, I just find it unfortunate that because of your wording it is possible to interpret what you have said as being that you support the point of view that the big bang was an explosion from a single point in space.

I am NOT saying that that's what you said (I see that it isn't), I'm just pointing out how you've left it open to misinterpretation.

 

[Mordred]

AAARRRRRHHHH ... I understand what you are saying and I am NOT saying it is wrong, I just find it unfortunate that because of your wording it is possible to interpret what you have said as being that you support the point of view that the big bang was an explosion from a single point in space.

I am NOT saying that that's what you said (I see that it isn't), I'm just pointing out how you've left it open to misinterpretation.

Don't you love the singularity misconceptions Phinds? To be serious the size of the universe at the beginning is an unknown size, the singularity in this case is simply a point where the maths no longer work.

 

[Mordred]

I have been contemplating the expanding universe theory with regard to the edge of the universe. As far as I am aware this theory resulted in the fact that if all motion in the universe was reversed then all would come together at a single point somewhere, which at that time would have been the whole universe.
If all started at a single point, and assuming time is imagonary i.e. just the rate of change, then the edge would now be 13.7blys away from that point. Using a simple diagram you can see that the oldest part of the universe would be at the center with age reducing as you move outwards. There are 2 problems with this picture 1 unless viewed from the center the universe would appear lop-sided regarding the age of what is seen 2 the furthest you could see would be half the age of the universe in light years. This picture puts everything inside an expanding circle looking towards the edge. This is what we appear to see but we do not see a lop-sided universe and we can see further than 7blys.
If time is real, being discussed in another thread, then a universe expanding in time and space should produce something closer to what we actually see, the universe would look the same in all directions and we would be able to see almost to the beginning, but would put us on the edge of the circle looking in which would put the edge of the universe not in space but just in front of us in time, strange as that might sound.
Of course if what I have read regarding the expansion of the universe from its beginning is incorrect then I will have to think again.

Sorry if your analogy were true we would have a preferred direction, that preferred direction would be towards the center. Expansion would have different rates depending on which direction we look. Large scale structures would form at different points depending on which direction we look.
None of this occurs, there is no preferred direction. Expansion occurs the same regardless of which direction we look. This discounts the possibility of expansion radiating outward from a central point regardless of the size of that central point.

 

[phinds]

Don't you love the singularity misconceptions Phinds?

Yeah ... I had the same problem when I started looking at cosmology, so it doesn't bother me that others have that misconception, what BOTHERS me is that some of them just hang on to it and hang on to it and hang on to it ...

So anything that helps them hang on to it also bothers me, thus my response to julcab12 who made a perfectly valid analogy that just had the unfortunate problem of being overly susceptible to misunderstanding.

 

[Mordred]

Part of the problem there is there is tons of pop media you-tube videos etc that describe it in just that manner. Some of the worse is the ones that imply some form of "God particle (used to represent GUT). Those are the ones I truly hate. Especially considering You tube is a popular source of information for those wishing to learn cosmology

 

[julcab12]

AAARRRRRHHHH ... I understand what you are saying and I am NOT saying it is wrong, I just find it unfortunate that because of your wording it is possible to interpret what you have said as being that you support the point of view that the big bang was an explosion from a single point in space.

I am NOT saying that that's what you said (I see that it isn't), I'm just pointing out how you've left it open to misinterpretation.

Haha. Well. I failed, should have used better wording. Dilemma of oversimplification.

 

[sukini3]

Has anybody brought up the bubble theory within the multiverse theory? How about the 11-dimensions creating the possibility of all possibilities within eleven dimensions? That would assume infinite space and time, if not in our three dimensional universe.

 

[phinds]

Has anybody brought up the bubble theory within the multiverse theory? How about the 11-dimensions creating the possibility of all possibilities within eleven dimensions? That would assume infinite space and time, if not in our three dimensional universe.

I suspect that no one has brought those up because this forum is for the discussion of actual science, not totally unproven speculation.

 

[sukini3]

I suspect that no one has brought those up because this forum is for the discussion of actual science, not totally unproven speculation.

That's mostly fair, and I CERTAINLY won't argue the bubble universe, but I believe that the 11- dimensions come from the mathematical models from the string theory? Again, I know very little about this topic and I apologize for the pseudo-science

 

[phinds]

That's mostly fair, and I CERTAINLY won't argue the bubble universe, but I believe that the 11- dimensions come from the mathematical models from the string theory? Again, I know very little about this topic and I apologize for the pseudo-science

String theory holds HUGE promise but there are two problems.

1) It has held that promise for over 20 years and has gone nowhere. LOTS of very smart people have spent huge amounts of time on it, because of the potential, but it has gone nowhere.
2) There is exactly zero empirical evidence for it.

EDIT: by the way, I don't mean to imply that string theory is not a valid topic for this forum but extending it to cosmology as you did is WAY premature.

 

[timmdeeg]

It is assumed that the big bang wasn't a pointlike singularity, rather the size which represented the observable universe at that time was in the order of the Planck scale.
Now, going back in time things get closer together and each point in today's observable universe will be represented by its respective worldline. However, arriving at Planck scale the density of the worldlines would be << Planck length. Do we thus have to think of an "no worldline epoch"? Sorry for this weird question.

 

[Boy@n]

I think it is possible to see the birth of the unvierse in the futre, but it won't be via light or by the universe's expansion for the reason phinds pointed out. But there are two types of radiation that can penetrate the surface of last scattering.
1 neutrinos , these could take us back to about 2 seconds after the big bang.
2 gravity waves, these could go even earlier and some have suggested even before the big bang itself.

The technology needed for this is not going to happen in the next fw years in my opiion, it's somewhat scifi but it is not impossible.

Sounds probable to be true...

Phinds, Mordred?

 

[phinds]

Sounds probable to be true...

Phinds, Mordred?

Yes, there have been several proposed ways that we will be able to see past the surface of last scattering and those are two of them. I'm sure there are others but I don't recall what.

 

[Mordred]

The neutrino measutements holds the best promise of seeing further. However the second option is also viable. Technology still has a ways to go however.

 

[Mordred]

That's mostly fair, and I CERTAINLY won't argue the bubble universe, but I believe that the 11- dimensions come from the mathematical models from the string theory? Again, I know very little about this topic and I apologize for the pseudo-science

thats essentially correct. String theory isn't something I am too familiar with however

 

[Adrian07]

phinds re post 80. I am not hanging onto misconceptions only repeating what others have written, if what is written is incorrect then that is not my fault but the fault of the academics that have come up with these ideas, I have no personal preference and do not actually think the BB theory is correct.
Perhaps you could give a short explanation of what you believe to be true, including where inflation fits in and how things could have started from a quantum fluctuation and which does not include starting from a point.

 

[phinds]

phinds re post 80. I am not hanging onto misconceptions only repeating what others have written, if what is written is incorrect then that is not my fault but the fault of the academics that have come up with these ideas, I have no personal preference and do not actually think the BB theory is correct.
Perhaps you could give a short explanation of what you believe to be true, including where inflation fits in and how things could have started from a quantum fluctuation and which does not include starting from a point.

No serious academic promotes the idea of everything starting from a point. For one thing it would imply a lack of the isotropy which is so clearly evidenced. If you think the BB theory is incorrect, I'd say that's likely because you don't understand it. The BB theory says NOTHING about how everything started, quantum fluctuation or otherwise. It is about everything that has happened from about one Plank time after the singularity (whatever THAT was) and NOT about how it started.

Early inflation is a contentious subject and not proven. It does solve some problems but still is not proven or totally accepted.

 

[Mordred]

First let's clarify the BB model.

The BB model does not start from a point. The singularity described as mentioned numerous times is simply where the math no longer works.
The early inflationary models utilize the quantum fluctuations. False vacuum is now called old inflation.
There are over 100 models dealing just with the inflationary era. Some use the Higgs field. Some the inflaton field. Some use other mechanisms.
The inflationary era is still poorly understood.
The BB model has its sucesses however its also important to realize that in actuality its a collective of good fit to observational data models.
The current concordance model. Which is a term for the standard model (not necessarily the most popular) is tha lamddaCDM model.

Inflation era is sometime in the first second. Depending on which inflationary model your using. Commonly though its at the beginning of the ekectroweak epoch

 

[Mordred]

If you truly want to understand the LCDM or $\Lambda$CDM model and what we have learned compared to observational data I would suggest reading this review. Its written in an easy to understand format that doesn't require a lot of previous knowledge.

http://arxiv.org/abs/1304.4446

however its not designed to teach the model, its only designed to provide a descriptive and comparison to observational data

 

[Adrian07]

I thought we were talking about what happened after it started I.e how it got to where it is now from where it started. Either it expanded from a very small space into what we see now or is there another explanation. Are you saying that if the expansion we see was reversed then it would not end up at a single point. I am trying to understand expansion that does not expand out from a central point unless the expansion is from many central points i.e. there was more than one starting point. Forget how it started and explain expansion from the one plank time or from where it was say the size of a pea or melon where it would have had an obvious edge at least to an outside observer.

 

[phinds]

...Are you saying that if the expansion we see was reversed then it would not end up at a single point...

YES ... good, you are finally getting the point (no pun intended)

I am trying to understand expansion that does not expand out from a central point unless the expansion is from many central points i.e. there was more than one starting point. Forget how it started and explain expansion from the one plank time or from where it was say the size of a pea or melon where it would have had an obvious edge at least to an outside observer.

The expansion did not HAVE an "outside edge". The expansion was of everything there is. If there had been something "outside" of it, that would have been part of everything there is and thus would have been part of the expansion. The expansion did not happen INTO something.

 

[timmdeeg]

I thought we were talking about what happened after it started I.e how it got to where it is now from where it started. Either it expanded from a very small space into what we see now or is there another explanation. Are you saying that if the expansion we see was reversed then it would not end up at a single point. I am trying to understand expansion that does not expand out from a central point unless the expansion is from many central points i.e. there was more than one starting point. Forget how it started and explain expansion from the one plank time or from where it was say the size of a pea or melon where it would have had an obvious edge at least to an outside observer.

The universe started at Planck scale, at least according to present mainstream. At that time, as today, it obeyed the cosmological principle which means each point looks the same, there is no center and no edge.

 

[phinds]

The universe started at Planck scale, at least according to present mainstream. At that time, as today, it obeyed the cosmological principle which means each point looks the same, there is no center and no edge.

I would disagree that the universe started at the Plank time. What I would say is that our understanding of the universe, as expressed in the Big Bang Theory, started at the plank time. What happened before the Plank time is what we call the singularity (meaning we don't know WHAT it was) but IT was the start of the universe.

 

[timmdeeg]

I would disagree that the universe started at the Plank time. What I would say is that our understanding of the universe, as expressed in the Big Bang Theory, started at the plank time. What happened before the Plank time is what we call the singularity (meaning we don't know WHAT it was) but IT was the start of the universe.

Well, it depends on what you call universe. The earliest period from which the Lambda-CDM model starts is the Planck epoch. What is the physical meaning of before Planck time? Should there have existed something - a quantum fluctuation perhaps - was is part, just cause or both, related to the universe?

 

[julcab12]

In addition to shy away from enigma of analogy.

In theory(Model), At the very moment of the big bang(not a bang) all the points(let's just say its a point for now) in the universe were at 'infinitesimal distances' from each other; that's what is meant by calling it a "singularity". In mathematical term, immeasurable or its variable limit rest and break @ 0 or in common language, "It doesn't make sense". But on top of it all. It is not really known whether or not the universe started(uncertain/temporal start) from a singularity or not. So what they did. They catalog it as a series of events not mainly the start of the universe but a start of an EVENT.
The cosmos at the start of the big bang are mostly unproved conjecture. And yet we have to deal with it somehow.BTW QP is doing a nice job.^^