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Brandon-
climber
The Granite State.
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He may be the 'celebrity' physicist , but Brian Greene lays things out in a fairly understandable way.
Paging Ed.
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Mike Bolte
Trad climber
Planet Earth
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John G. - that is correct. The "expansion" of the Universe is the creation of spacetime.
LEB, at least get caught up to 1916. *Four* dimensions! You want to have an event in this Universe: say you and DMT are going to meet somewhere for coffee. You better specify the three spatial dimensions AND the time or your world lines won't intersect.
EDIT: by the way John, it is a pleasure to be posting on the same thread as you! I was completely inspired by Master of Rock. When I came face to face with some of your problems at the Needles and Vedauwoo, I realized there were other universes of rock climbing levels
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laughingman
Mountain climber
Seattle WA
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When you look into the night sky you are looking "back" in time. Observable light only came about (300,000?) years after the big bang.
That the reason composite pictures from WMAP only go back to 300,000 years after to big bang
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laughingman
Mountain climber
Seattle WA
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If it's finite, what's on the outside of it?
That is a conversation for philosophers and monks not scientist...
Due to the the fact we have no observable proof...
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Mike Bolte
Trad climber
Planet Earth
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hmmm laughingman I don't quite know what you are talking about - the cosmic microwave background and the hot and cool spots (only one part in 100,000) you can see in the WMAP image can be thought of as looking back in time to the "surface of last scattering". For the first 300,000 years after the Big Bang, the Universe was so hot that all the atoms were ionized. Photons have a short travel time in an ionized gas before they are scattered off of an electron. So, for the first 300,000 years the Universe was opaque or foggy. At around 300,000 years, electrons recombined into hydrogen and helium atoms and the Universe became transparent to radiation.
We can see that transition in the WMAP image. We can't see into the young (t<300,000 years) universe, only make inferences about what went on there.
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Ed Hartouni
Trad climber
Livermore, CA
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I can tell you all are experts at this space-time geometry thing... so I'm sure that you will have a lot of criticisms of the idea of what an "infinite" or "finite" universe is...
Recall the important observation of Edwin Hubble that every point in the observed universe is moving away from every other point, also known as the expansion of the universe, or, more technically the "metric expansion of space."
Einstein's Theory of General Relativity, which is about gravity, also provides the tools to understand the consequences of "metric expansion." One eventually comes to the Freidmann equation relating the rate of expansion to the curvature of space-time, in terms of the density of the universe.
In the "non-relativistic" limit, the only way a particle can escape the universe, i.e. to have a total energy greater than zero (which would take it to infinity), is if the curvature is negative, or zero. If the curvature is positive, the particle cannot "escape" and we call the universe finite.
The fact that there was a big-bang does not necessarily determine whether the universe is "finite" or "infinite."
Current cosmological prejudice is that the universe is flat, that is curvature of 0 where the kinetic energy balances the potential energy. So the universe could be infinite if K=0.
The same could be true for K=-1, infinite universe, but it is possible to construct finite spaces with K=0 or -1 which are consistent with observation.
K=+1 is a finite universe.
In this cosmological setting, the universe could be dominated by cold matter (like dust), hot matter (like radiation) or with vacuum energy. Each of these have different consequences. And what kind of matter dominates in what epoch could also change. That is the current direction of investigation, particularly with regards to vacuum energy.
To answer donini's question: yes, the universe could possibly be finite. Enjoy the Atacama desert, by all accounts one of the more remarkable places on Earth to go... hopefully I will make it one day... lots of invitations.
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laughingman
Mountain climber
Seattle WA
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hmmm laughingman I don't quite know what you are talking about - the cosmic microwave background and the hot and cool spots (only one part in 100,000) you can see in the WMAP image can be thought of as looking back in time to the "surface of last scattering". For the first 300,000 years after the Big Bang, the Universe was so hot that all the atoms were ionized. Photons have a short travel time in an ionized gas before they are scattered off of an electron. So, for the first 300,000 years the Universe was opaque or foggy. At around 300,000 years, electrons recombined with hydrogen and helium atoms and the Universe became transparent to radiation.
We can see that transition in the WMAP image. We can't see into the young (t<300,000 years) Universe, only make inferences about what was going on based on what we know of physics.
Got my stuff mixed up, my bad
fixed my post
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WBraun
climber
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To answer donini's question: yes, the universe could possibly be finite.
That's not an answer.
That's still the question ......
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Ed Hartouni
Trad climber
Livermore, CA
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I think that is an answer...
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k-man
Gym climber
SCruz
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Easy to imagine time as the fourth dimension.
The bar door is three dimensional. At a certain time, I will be opening the door. The fourth dimension places me at a specific X+Y+Z place at a time. With time, the door changes.
At least that's what somebody told me.
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laughingman
Mountain climber
Seattle WA
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What if proof were discovered by a scientist?
What about theoretical proof?
What happens outside the observable universe is not really subject to "science" since it cannot be observed and thesis about the subject cannot be "tested" using scientific method. The subject of what happens outside the universe is a math based object of study.
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aguacaliente
climber
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There is a distinction between the observable universe and the whole universe. We can only see out to some distance (called the horizon) because the universe has a finite age, so we can only see back to close to the beginning. Light emitted from the horizon at the beginning is just reaching us now. So the observable universe is finite, but it is most likely embedded in a much larger universe.
Now, it could be that some distance outside the horizon, the universe has an edge, or just stops, or there is a cliff with big scary dragons at the bottom. We can't tell because we can't see it.
However, scientists assume that we don't live in a special place in the universe. Rather that another observer in a different place would see approximately the same that we do. This is usually called the Copernican principle. Any theory that requires that we live at a particularly special place or time is inelegant. This principle has some successes, for example early models of the Milky Way galaxy put us at the center, which is unusual, and now we know that was incorrect.
So it would be odd for us to live in a place where the observable universe looks normal, while Glork the alien who lives nine thousand megaparsecs to the left sees us on one side and the cliff with scary dragons on the other.
If you extrapolate the geometry of the part that we can see and apply this principle to say that the part beyond the horizon is similar, then it works out that the universe is spatially infinite.
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Dingus McGee
Social climber
Laramie
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Is it possible to confirm INFINITY in a physical measurement such as mass?
Is it possible to realize the extent of space?
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Norwegian
Trad climber
Placerville, California
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mr mcgee i've wrestled infinity,
and though it is slippery
i've well harnessed it and rode it to oblivion,
the symbol for infinity is a drunk 8
fold the inebriated eight at it's vertical axis
and it becomes zero.
now twist zero about it's center
and it becomes again sober infinity.
so everything, even taxes,
is a journey from drunk to sober.
a dance between absolute nothing and unfathomable everthing.
the universe is a virgin and
and gave birth to our earth
via a big 'ol bang announcing her unassisted cumming.
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Eric Beck
Sport climber
Bishop, California
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Here is a way to think about a finite yet unbounded universe. Imagine two spheres. Join them at their surface. Then, when flying around in this space, when one passes through this surface, one enters the other sphere, never encountering any boundary or scary dragons.
I don't propose any answer to the original question of finite/infinite.
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Dingus McGee
Social climber
Laramie
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Mark what you measure so you don't measure it twice.
Nevermind, multiplication by 2 doesn't produce infinity.
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Ed Hartouni
Trad climber
Livermore, CA
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not sure if this will help, but the physicist's view is pretty simple...
let's dial it back to Earth for a moment
you have an apple in your hand, you throw it up into the sky, it comes back down
you throw it harder, it goes farther but comes back down, eventually
the question is, can you throw it hard enough so that it does not come back?
That has an answer, and it also defines what "finite" and "infinite" means. If the apple always "returns" the universe is finite, if it does not return, the universe is "infinite."
Now replace the "Earth" with all of the universe and you've got the concept of "infinite" and "finite."
So the answer to the question "can you know if the universe is infinite?" is answered by "weighing" the universe. We have done that... the universe appears to have a "weight" equal to the total kinetic energy (the energy of "motion"). This universe is a "flat" universe, space-time has no overall curvature.
One can elaborate from here in a number of directions.
You may protests "but if the universe is finite, what's beyond it?" but the question, while interesting to contemplate taking in the vast beauties of our tiny, no, our infinitesimal place here in the universe, doesn't mean anything since it is a place that we cannot go.
There is no there there.
So it's easier to think of the universe as being infinite, it is a particular solution that reassures our conceit that we have no bounds.
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Reilly
Mountain climber
The Other Monrovia- CA
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I need a drink, as long as my bottle is still there there. But thanks anyway, Ed. :-)
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cintune
climber
Midvale School for the Gifted
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