Is the universe finite or infinite?

Ace Modder said:
If the universe was a weird paradox which looped on itself - would that be classed of infinite or finite - the space has a max dimensional size to it if you start measuring at from one end of the loop to the other - but then you could travel infinitely in a single line???
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How would that be a paradox? Take a ball and draw a line around the circumference. You'll find that your pen will end up back where it started – shock, horror!
 
DAnDan said:
Not true. Shine a torch from close up, you'll see it, shine the same torch from further away, you won't. Light follows the inverse square law, basically stating that the further away you get, the dimmer the light gets, to the point where it is too dim for us (as in people) to see. Hence why cameras/telescopes/etc can see more stars than we can.
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Except if you shine an infinite number of torches, the inverse square law wouldn't matter. The reason the entire night sky isn't bright is because the universe is of a finite age.
 
lord filbuster said:
Except if you shine an infinite number of torches, the inverse square law wouldn't matter. The reason the entire night sky isn't bright is because the universe is of a finite age.
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Why would it not matter? If you have two torches instead of 1, it just starts twice as bright, and then follows the same law.
 
The universe did not "begin" imo, as for that to happen you have to put a definite date and time for when that happened.

i think the main problem with humans is that we perceive things apparently starting and ultimately finishing and we place markers in our memory as to this happening. These events are always something we can comprehend in the scale we live our lives.

However, if, for example, you take the life of a human, we see the point when we are born as its start and the point when we die as its end, but that simply isn't the case, it certainly is for the complex set of interactions we call a consciousness, but it isn't for the chemicals and compounds that made that consciousness a possibility.

We are born of star-dust and ultimately all we now are will, in some form, end back up as star dust. The universe is not just unending, it is impossible to apply any form of measurement to it. At no point did it go from being to not being, it has simply altered its state. There is no reason for this to have begun at a designated point in time (note: this does not discount something like the big bang occurring, in the same way as it does not discount the birth of a new life) and there is no reason it will ever end, only change.
 
Ah, I love it when GD solves problems that have baffled scientists for such a long time!

Join us next week for GD talks about stuff it knows nothing about : mavity - what's that all about then, eh?
 
Space = infinite
Universe (as we know it) = finite.

The universe is expanding and for something to expand/grow it must have a measureable end point. Just because we don't have the technology to define this measurement does not mean it isn't so. Space, like time is infinite as it has no measureable end.
 
DAnDan said:
Why would it not matter? If you have two torches instead of 1, it just starts twice as bright, and then follows the same law.
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The luminosity of an object is the Flux=F divided by 4*pi*r^2. Since the combined flux from an infinite number of stars is infinity, the equation becomes infinity/4*pi*r^2. Therefore the luminosity is infinite, regardless of the value of r.
 
lord filbuster said:
The luminosity of an object is the Flux=F divided by 4*pi*r^2. Since the combined flux from an infinite number of stars is infinity, the equation becomes infinity/4*pi*r^2. Therefore the luminosity is infinite, regardless of the value of r.
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But there's isn't an infinite number of stars, so that doesn't apply.

Also, are you not just calculating the light at the source, not taking into account the distance from the object to the point of observation, as you have no distance term in that equation?
 
DAnDan said:
But there's isn't an infinite number of stars, so that doesn't apply.

Also, are you not just calculating the light at the source, not taking into account the distance from the object to the point of observation, as you have no distance term in that equation?
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The r is the distance term, it is the radius of a sphere that is centred on the object, with the edge touching your retina/lux meter. The total flux from all the stars would just be L1/4*pi*r1^2 + L2/4*pi*r2^2 + .... .
There may be an infinite number of stars, it could be that the light from them hasn't reached us yet, but it may also be that there are a finite number of stars. Either case could be true.
 
Ask again when we define the universe and everything in it :D

It's like asking, why did Torres move from Liverpool to Chelsea without having a concept of cash..
 
lord filbuster said:
The r is the distance term, it is the radius of a sphere that is centred on the object, with the edge touching your retina/lux meter. The total flux from all the stars would just be L1/4*pi*r1^2 + L2/4*pi*r2^2 + .... .
There may be an infinite number of stars, it could be that the light from them hasn't reached us yet, but it may also be that there are a finite number of stars. Either case could be true.
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You've still not considered the distance between the object and the observation point though. Obviously if your retina is touching the light source you don't consider it, but we're talking about over very large distances here.

So no matter how much light each star puts out, it will fade inversely with distance squared.
 
DAnDan said:
You've still not considered the distance between the object and the observation point though. Obviously if your retina is touching the light source you don't consider it, but we're talking about over very large distances here.

So no matter how much light each star puts out, it will fade inversely with distance squared.
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The r isn't the radius of the object, it is the distance from the object to your eye, the star itself can be considered a point source. The reason you calculate the distance as a sphere is to account for the fact that the object radiates in all directions. An object of infinite flux would appear infinitely bright regardless of distance.
 
The observable universe is finite, the universe is sufficiently bigger than that so as not to leave a mark on the observable universe. I believe the closest to a consensus view is that the universe is finite but curved back on itself so that you can travel continuously in any direction without reaching any edge.

Me, I think its infinite.

Oh, and it's not expanding "into" anything. That completely misunderstands the expansion of the universe.
 
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