Many scientists/astronomers say that the Universe is finite. I think what they mean to say is that the mass of the Universe is finite, or that the space occupied by the mass in the Universe is finite. However, I think this raises a series of appropriate questions:
1) What is "the Universe"?
2) Is the Universe finite?
3) If the Universe has a bound, what is on the other side of that bound?
This may be as philosophical as it is scientific in nature.
| benjmd wrote: |
Many scientists/astronomers say that the Universe is finite. I think what they mean to say is that the mass of the Universe is finite, or that the space occupied by the mass in the Universe is finite. However, I think this raises a series of appropriate questions:
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My own experience is that astronomers in particular, and scientists in general tend to be careful about statements like that and would normally either qualify it or, much more commonly, closely define what they meant in terms of spatial and temporal dimensions.
I think that trying to tell an astronomer what he means would be a tad impertinent for a non astronomer, but I'll give my view which I think is fairly mainstream and not likely to offend too many astronomers.
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1) What is "the Universe"?
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The Universe is the sum of matter/energy within spacetime, taken as a whole.
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2) Is the Universe finite?
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Don't know. Could be, likely not to be. Depends on the 'shape' or topography, the precise expansion and inflationary model used, and the presumptions made, if any, about t<0 at Big Bang.
I think that most astronomers would probably say that the universe is bounded in both spatial and temporal terms, but I qualify that with the warning that I am not an astronomer and not really qualified to speak for that body of science or scientists.
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3) If the Universe has a bound, what is on the other side of that bound?
This may be as philosophical as it is scientific in nature. |
Nothing. The problem is that you will very likely have a problem with the term nothing since I mean it to denote no spatial dimensions and no termporal dimension (no space and no time). Most people have a problem imagining what this means and this is normally the place where the discussion falls apart because of that.
Chris
PS - here is a paper I did on this a while ago which may be of interest.
http://camres.frih.net/resources/GeneralPhysics/universe-guide/universe-guide.htmWell, nothing is infinite. If it is, then let me know, because I can't think of anything.
We just happen to be such a small particle in relevance, that it could really go either way.
Think about it as the planet earth being an Ant, and the Milky Way Galaxy is the Universe. Ins not infinite, but in proportion, thats muy grande
Theres some interesting stuff in there, especially the shifts.
Okay, about the light from distant stars not reaching us yet, you are saying that when they do reach us, nighttime will have a pure white sky?? | benjmd wrote: |
Many scientists/astronomers say that the Universe is finite. I think what they mean to say is that the mass of the Universe is finite, or that the space occupied by the mass in the Universe is finite. However, I think this raises a series of appropriate questions:
1) What is "the Universe"?
2) Is the Universe finite?
3) If the Universe has a bound, what is on the other side of that bound?
This may be as philosophical as it is scientific in nature. |
These questions are really interesting indeed, but I'm afraid we have searched for answers several hundreds of years and we still haven't found anything really important. And our view on the universe is changing from day to day.[quote="Bikerman"] | benjmd wrote: |
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3) If the Universe has a bound, what is on the other side of that bound?
This may be as philosophical as it is scientific in nature. |
Nothing. The problem is that you will very likely have a problem with the term nothing since I mean it to denote no spatial dimensions and no termporal dimension (no space and no time). Most people have a problem imagining what this means and this is normally the place where the discussion falls apart because of that.
Chris
PS - here is a paper I did on this a while ago which may be of interest.
http://camres.frih.net/resources/GeneralPhysics/universe-guide/universe-guide.htm |
I am interested by your reply to #3 and it is precisely the reason why I remarked "This may be as philosophical as it is scientific in nature."
Dimensions only apply to things we can observe or measure. If "space" stretches for eternity without any occupying mass or energy, etc, there is no reference point from which to assign it a dimensional value. If we can't observe or measure it, let alone test theories about it that would require observation of measurement, it really goes beyond the realm of "science."
But that word "nothing" is, in fact, tricky. You're right that it is dimensionless, but I think (and this is a philosophical point, not a scientific one) that by the mere fact that you can assign it a descriptor of *any* sort, you prove that the dimensionlessness is *something.*
Through my torrid love affair with dictionary.com, I came on this appealing definition of "Universe": "the totality of known or supposed objects and phenomena throughout space" ...
I think I would agree that the Universe defined as such is finite. But what do we call the rest of that dimensionless space?? I think the universe is infinite.
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| 1) What is "the Universe"? |
The Universe is the physical system we live in.
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| 2) Is the Universe finite? |
What does finite mean in this context? I think the answer depends on your definition.
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| 3) If the Universe has a bound, what is on the other side of that bound? |
Nothing special. Suppose you find the boundary of the Universe. And then, you find something beyond that boundary. By virtue of the fact there is something beyond it, you can conclude that you have NOT found the boundary of the Universe.Finite: having bounds or limits; not infinite; measurable
I think your answer, "the physical system we live in," is interesting, but I would like to know what you mean by "physical system." I think you have just offered a different, slightly more explanatory name for "Universe."
What is the Universe? Some say it's everything that the world is composed. So is this finite or not? And what is this? I don't think that any scientist has the answer. One could ask about the human way of thought. Isn't it influenced by nowadays knowledge and ideas? Of course it is.
Scientist brains are measurably much more limited than the Universe.
Your questions, benjmd, are quite reasonable. Have you ever heard about string theory? The mathematical models of Universe (I still don't know what that is) may have a lot of new dimensions. And we are just counting with space and time. Remember when everybody thought that the Earth was the center of the world. This sounds familiar...
Hi people,
That´s a really really hard question.
I don´t know what to think.
How can be infinite - everything is finite - I guess. Should be some the end - maybe there are so many constelations, stars, etc, but should be the end some how.
| talonsmallville wrote: |
| How can be infinite - everything is finite |
There are plenty of abstract infinities. The velocity of a body in space is the derrivative of your position with respect to time. Finding the derrivative involves taking limits and taking limits involves resolving cases of infinity.As Tac-Tics says infinite concepts exist. Also finite concepts exist.
What about the Universe? I even don't know what that is, but let's try to guess a definition: it's everything that exist, will exist or existed in all of the forms possible.
When looking at the sky I see a 3D huge world: perhaps infinite. But look: even finite distances are crossed in infinite steps. Perhaps there's some mixure in concepts.
I'm guessing assuming this mechanical 3D concept based on my technological background...
With infinaty to us humans it is just a word (or equasion), can anyone imagen just going forever and ever and having no chance of reaching the end of nothing at all, weird 
Also with that i dont think the universe is infinate, if there was a big band, which i have noticed is the over riding thoery then there was in fact something that blew up, and something cannot expand to infinety.
Reddish Blue At currant technological state, at any technological stater, that is imposable to determine. Even if we found a way to travel anywhere in the universe instantaneously, even after trillions of years we'd still be exploring that galaxy's produced by the big bang.
| squirrelmaster wrote: |
Theres some interesting stuff in there, especially the shifts.
Okay, about the light from distant stars not reaching us yet, you are saying that when they do reach us, nighttime will have a pure white sky?? |
No. Expansion would seem to mean that it may never reach us, depending on the rate of expansion. Expansion can 'move' faster than c because the limits of relativity do not apply to spacetime itself, only to the contents of spacetime.
Also the 'white sky' presupposes an infinite universe which is not thought to be the case.
Chris.I think it really depends on what you mean by universe. Does universe refer to the emptyness, the "container", or does it refer to the contence. I will refer to the universe as the emptyness or space between, and cosmos as all "matter". The universe is emptyness with some matter spilled into it lol. I think the Universe is definately infinate, no doubt. Of course, the cosmos isnt .... then again, that depends on what theory you tend to like the most.
There should be no confusion. Our universe consists of space-time and everything in it..
I think it's too complex for people to understand this complexitiy. and people don't have the capacity to handel that kind of information. I think the 10th dimension is indeed all that we can handel Okay, I'm only a Sophomore in High School, but this is what I think about all this.
1). The Universe is the total amount of mass and energy that exists. Due to the laws of Conservation of Mass/Energy, there is a set amount of energy/mass which is constantly being changed between the two.
2). In regards to my above statement about a set amount of energy/mass I would say that the Universe would have to be finite.
3). This is the part that really confuses me when I think about this stuff. How can the Universe "end"? I think that there wouldn't actually be like a physical barrier of sorts, instead, there would simply be no more mass/energy. The gravity of all the mass would keep everything in a spherical area and outside that area would be absolute nothing. (We think of space as being "nothing", but it isn't entirely, there are tiny particles floating, different molecules, rocks, ect.) However, outside the spherical area, not even those would exist. It would be total nothingness.
Well this my opinion.We don't know. The expanding Universe theory says that the Universe could expand forever [that corresponds to a 'flat' Universe]. And that is probably the model of the Universe that we feel closest to now. But it could also be finite, because it could be that the Universe has a very large volume now, but finite, and that that volume will increase, so only in the infinite future will it actually be infinite.
Goodbye!
my idea is that the universe is infact finite, simply because there's enough evidence to conclude so.
But as for the other side of the boundry, that is open to speculation, my personal opinion is that on the otherside of the boundry is absolute nothingness, and you cannot penetrate or exist within nothingness because it is nothing.
It kind of hurts my head to think about for a long time though
| mastersedv wrote: |
| I think the universe is infinite. |
I believe the universe is infinite. Anyone who believes in a higher power should believe the same way. 
| Patsferpatrick wrote: |
my idea is that the universe is infact finite, simply because there's enough evidence to conclude so.
But as for the other side of the boundry, that is open to speculation, my personal opinion is that on the otherside of the boundry is absolute nothingness, and you cannot penetrate or exist within nothingness because it is nothing.
It kind of hurts my head to think about for a long time though |
okay, YES there is finite mass/energy of the universe, but there isn't a SET boundry where then there is nothing further than it. (the volume of the universe is like air, it expands and therefore is infinite)
The universe is expanding in the fact that galaxies are moving apart, but not in the sense of galaxies being created with new matter.
and also you could travel and exist in the "nothingness", because we can be in space, and it is almost identical except we don't have to worry about flying particles. | bluedragon wrote: |
| mastersedv wrote: | | I think the universe is infinite. |
I believe the universe is infinite. Anyone who believes in a higher power should believe the same way. |
Just as you suggest that believing in a higher power means that you should believe the Universe is infinite, I would clarify that I think believing that space (as discussed above, the term "Universe" might best be applied only to the matter and energy) is infinite should incline one to believe in a higher power. 
I think universe is infinte. there are many solar system within a universe... May be we can find ET's...
I think it's infinite.
"...and you just want to find the truth, but the truth is at the bottom of a bottomless pit." - A Civil Action
| benjmd wrote: |
Many scientists/astronomers say that the Universe is finite. I think what they mean to say is that the mass of the Universe is finite, or that the space occupied by the mass in the Universe is finite. However, I think this raises a series of appropriate questions:
What is "the Universe"?
2) Is the Universe finite?
3) If the Universe has a bound, what is on the other side of that bound?
This may be as philosophical as it is scientific in nature. |
1. Well in the simplest definition the universe is the invisible yet very real surroundings of every planet and every galaxy and every other matter out there.
2. Well I personally subscribe to more recent theory of Physics that the universe is infinite that it is ever expanding and that it is growing at an accelerating rate. As for whether or not I can proove that I can't and as flawed a logic as this may sound I just don't hear a very credible alternate theory. Then again who is to say who is right or wrong since nobody has ever actually tried to reach the end of the universe only to hit a wall or something (outside of futurama episodes 
) or to find that the universe just keeps expanding.
3. a parallel universe is possible, but thats only assuming there are parallel universes out there but then that raises even more questions like is that bound by a bigger super universe?
As for the last comment it is a matter of science vs. religion as we all know some people like copernicus or gallileo were literally lampooned for their radically different ideas on the universe (and where even given a mountain of evidence prooving what nutcases they were thought to be at the time) of course now we all know differently and todays truths may well become yesterday's lie.I'm not familiar with the 'more recent theory' quoted here. My understanding is that the Universe is finite but possibly unbounded. The distance to the cosmic dawn (correctly called the cosmic light horizon) is more than 13.8 billion light years (current estimates are between 45 billion and 75 billion depending on assumptions about the hubble constant). The universe age is currently set at 13.8 billion LY. The reason is expansion which means that the intergalactic space has expanded and thus the glalaxies appear much further apart than one might expect. The distance to the cosmic light horizon is the size of the observable universe. Outside this is beyond physics because unobservable phenomena are not in causal relationship with us and can be ignored.
Chris.
If the universe is infinite, then there are an infinite amount of copies of you all around the universe. You would not be unique.
| Bikerman wrote: |
I'm not familiar with the 'more recent theory' quoted here. My understanding is that the Universe is finite but possibly unbounded. The distance to the cosmic dawn (correctly called the cosmic light horizon) is more than 13.8 billion light years (current estimates are between 45 billion and 75 billion depending on assumptions about the hubble constant). The universe age is currently set at 13.8 billion LY. The reason is expansion which means that the intergalactic space has expanded and thus the glalaxies appear much further apart than one might expect. The distance to the cosmic light horizon is the size of the observable universe. Outside this is beyond physics because unobservable phenomena are not in causal relationship with us and can be ignored.
Chris. |
could you explain this 'cosmic light horizon' a little further, i think you mean the boundary where the universe stops?
i do get the last sentence though--what does knowing whether the universe is finite or not have anything to do with us humans?
(unless some kind of dimensional/time travel depends on it)Wow, this is one of the most interesting conversations I have seen on this site. I love everybody's input. Anyways, I have never studied Astronomy nor real Physics but I would love to believe that at the end it starts again. I don't know. Has anyone seen the end of Men in Black II (I think), when they see that the universe is just a little thing in a locker or something. I don't know. I liked that idea.
| squirrelmaster wrote: |
Chris.
could you explain this 'cosmic light horizon' a little further, i think you mean the boundary where the universe stops?
i do get the last sentence though--what does knowing whether the universe is finite or not have anything to do with us humans?
(unless some kind of dimensional/time travel depends on it) |
Sure,
the light horizon is the boundary where the universe WOULD have stopped if expansion were 0. Another way of putting it is that the CLH is the region of space which could have interaction with us (because it is within reach at speeds of c or less). Anything beyong the CLH is beyond the speed of light and therefore incapable of interaction with us and therefore unknowable and not worth considering.
The question of whether the universe is infinite is one of the big ones....what it has to do with humans is largely a question of what it is to be human. Humans seek answers and this is a big question.....
Chris.thx, i get it now.
And yes, humans are always thinking for answers the universe as per me is the biggest mystery in this universe.
we wouldnt find an answer for this mystery
even if we find we definitely wont be able to verify it.
this is only my opinion
| venom wrote: |
the universe as per me is the biggest mystery in this universe.
we wouldnt find an answer for this mystery
even if we find we definitely wont be able to verify it.
this is only my opinion |
Ermm....hmmm....the universe is the biggest mystery in the universe....hard to argue with that I guess...
Finding an answer is possible, though I personally doubt whether any scientific model can be 'exactly' desctiptive of reality (the map is never the territory). A model which is consistent, accurate, predictive and repeatable is the best we can hope for - and would be a very fine achievement indeed. Such a model is, I think, within the grasp of physics...
Chris.1) What is "the Universe"?
Everything you see and everything you don't.
2) Is the Universe finite?
Depends on your definition.
3) If the Universe has a bound, what is on the other side of that bound?
The universe. Considering that if there is a boundary, and there is something after the boundary, then since the universe is everything, it is part of the universe.
I m really in doubt. Finite or infinite!
I prefer infinite.Bcoz we hav no boundery. Everything is rushing through the deep space.
| Physicist wrote: |
I m really in doubt. Finite or infinite!
I prefer infinite.Bcoz we hav no boundery. Everything is rushing through the deep space. |
Infinite can be bounded.
The following summary is taken from Sec-Ware at the following :
http://antionline.com/showthread.php?t=274089&page=2
Simple question: How often do I have to throw a dice in order to be 100% sure to throw
at least once a "1".
Simple answer: 6 times....well, that's wrong.
Correct answer: infinitely many times.
The probability in one throw not to hit the "1" is 5/6. The probability in two throws not to hit the "1" is (5/6)^2 = 25/36, and in n-throws (5/6)^n. Thus, the probability to at least hit the "1" once in n-throws is 1-(5/6)^n. This probability now should be 100% = 1. Hence, in order to be 100% sure to hit the "1" at least once, one has to throw
n = log(1-1)/log(5/6)=log(0)/log(5/6)= infinity times....interesting, isn't it?
I tricked. Of course, because the question we face here is a different. There are two important ingredients to consider. First, does our system have a memory, second, is our system countable infinite, or uncountable infinite.
Remark: Human beings assume when playing Roulette that the wheel has a memory. It doesn't!!
definitions
Let me allow to draw the following picture:
- an "item" is represented by a dice with n-faces. E.g. n=6, the dice has 6 faces with labels 0,1,2,3,4,5. This is my "variance". If n < infinity, then the variance is finite, if n is infinite, then the variance is infinite (more precise: countable infinite).
- the "space" is completely filled with the dices, thus we have a "memory" (as opposed to the above calculation). If the number of dices is finite, space is finite, if the number of dices is countable finite, then space is countable finite, if the number of dices is uncountable finite, then space is uncountable finite.
- a "cluster" is a connected set of particular items. A finite set of items in a cluster makes it a finite cluster etc.
finite variance and finite space
Let's fix the ideas to n=6 (a dice). All calculations are feasible, because variance and space are finite.
Example: 100% probability to have at least one replicant: space must be of size 7 (7 dices).
Certainly, one can calculate the size of "space" needed to find at least two clusters consisting of two "1", three "1" etc. with 100% probability....so, what is the size of needed "space"? Right, countable infinite!
For example you can calculate the "space" needed to find two Francos...just do not forget to incorporate that an human-being friendly environment also is needed. Hence, in order to find two Francos, you need to find aan earth-like planet in a solar-system like environment...again, what is the size of needed "space"? Right, countable infinite.
infinite variance and finite space
It becomes trickier as you may imagine, since the probability to actually throw a "1" (remember: a memory is present) actually is lim(n -> infinity) 1/n = 0.
Thus, mathematicians assume for their calculations that n is finite - perform their calculations, and then let n go to infinity.
Does that make sense? yes, usually, it does. A simple example:
- n -> infinity
- n!=n*(n-1)*(n-2)*... -> infinity.
- However, n/n! -> 0 for n-> infinity. Why?
n!=n^2*(1-1/n)*(n-2)*...
n/n! = n/(n^2*(1-1/n)*(n-2)*...) = 1/(n*(1-1/n)*(n-2)*...) -> 0 for n -> infinity
In this way, the probabilistic calculations can be done. Anyway, while some numbers must be there, the probability to find a replicant if the variance is infinite is zero.
finite variance and infinite space
While it is intuitively true that every cluster has a replica of itself, it actually is only true depending on certain circumstances:
if the cluster-size is finite, then this is correct. I guess this is what the thread-starter meant.
if the cluster-size is countable infinite, then this is only correct of space is uncountable infinite. if the cluster-size is uncountable infinite, then I have no idea.
An example to illustrate this point:
- finite variance: 0,1,2,3,4,5,6,7,8,9
- an (ordered) cluster (of size 3) consisting of 2, 3 and 7 can be represented as a real number |R: 2.37.
Thus, the set of real numbers can represent clusters of any size.
- countable infinite space can be represented as integer number |N_0
-> Since the set of integer numbers |N_= is a null-set in the set of real numbers |R, you cannot guarantee for replicas!
-> However, how do you define a "replica". Here, I was extremely restrictive by demanding ordered cluster. Combinatorics allows for additional factor, which may change the result enormously (for simplicity, I
have not mentioned it above).
infinite variance and infinite space
This gets more and more complicated, but you have to throw in the limes-technique described above (probabilistic), combinatorics, plus the discussion about countable/uncountable infinite sets. I guess, myself I would now spend hours over hours to work it out - for the particular cases.
Regards
Chris
