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Bethany Cobb: In Galileo's Footsteps

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Commonwealth Club of California

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Periergeia Avatar
Posted: 05.29.10, 11:20 AM
The question of the expansion of the universe is, by its very nature highly confusing. After all, we are used to be dealing with rigid Cartesian coordinate systems only! All of human experience is shaped by the biologically pre-defined assumptions that all of space is described by three orthogonal dimensions and that Volume is the product of these three dimensions for a given subdivision of this space. Unfortunately for us, the universe has tricked us into believing this by being very, very large, and rather old (on the biological timescale). What we see as space is in reality nothing but a tangent space of the real thing, i.e. it's a small scale flat, short time approximation of a region of weak gravitation. The situation is not much different from the difference between the curved surface of the Earth, which is a pretty good sphere, and the local impression which we get when we look from horizon to horizon: the Earth looks like a flat disk! That's because the locally visible part of the tangent space to a sphere happens to be a flat disk shaped region (with a sky dome on top, if we add the atmosphere)! But just as our perception of the Earth's surface changes when we are in a very high flying plane or spacecraft (the Earth becomes part of a sphere and the atmosphere changes to a thin shell around it), our perception of the universe changes when we are looking very far away or when we are looking at strongly gravitating regions of space like those that can be found around black holes or (due to the scaling properties of gravitation) galaxy clusters which show gravitational lensing. But while the analogy to the Earth's horizon is a pretty good one on some level, it breaks down on some other. For one thing, the static notion of volume that we have is not realized by the universe. Volume elements in a Universe obeying Einstein's theory of general relativity (or many similar theories that are possible but can not be distinguished from it based on available experimental data) can not be static. They either have to expand or contract. What this means is that nature CAN NOT implement a rigid yardstick! Any two points chosen at one time in space will have some, albeit slow relative motion to each other. In the case of our current universe, that motion seems to be an accelerating expansion. There are pretty good signs in recent developments in theoretical physics that what we perceive as "space" and "time" are emergent phenomena of some kind of thermodynamic system. One can, on a very crude level, think of spacetime as a gas that has no enclosures and that will expand forever into a real vacuum (which in case of the universe would be an invisible and unmeasurable quantity, at least on the level of current physical research). Please note that this is, indeed, a very crude analogy, because it tries to convey a feeling for what is really happening: in any thermodynamic system the entropy (the state of disorder) is an ever increasing quantity. In just the same way, the entropy of the universe is ever increasing. This means that in the beginning it starts out as a highly ordered system (in a small volume of space) and then decays into a highly disordered system (in an enormous volume of space). And if one is to trust Einstein's equation, which have proven to be extremely resilient to newly found evidence, the gravitation in the universe, and with that the way we measure volumes of space, are indeed, in a very complicated manner, emergent thermodynamic phenomena like pressure in a gas, which is nothing but the random exchange of momentum of gas molecules with walls that we install. Now, the jury is still out on this. The research that has led to these insights is a mere 40 years old and we have major missing pieces to the puzzle, like dark matter (the easy part) and dark energy (the one and only real enigma of modern physics), but a very existing picture has been emerging over the last century. The good news is, that while we are increasing our knowledge, we are looking at an increasingly more fascinating cosmos. The medieval sky dome has given away to Galileo's and Kepler's solar system, which gave away to a galaxy filled with billions of stars, which is not giving away to a universe of unimaginable geometric complexity and size. And it can only get more exciting from here!
pierr0t11 Avatar
Posted: 03.10.10, 05:44 PM
Why is the universe not homogenous?
MartinC Avatar
Posted: 02.11.10, 02:31 PM
Regarding the first post - My understanding is that everything in the universe was created at the big bang, including the dimensions of space and time. So it is impossible for a human to imagine what the universe is expanding into because there is no dimension of space outside the universe. To be able to stand outside the universe and witness it's expansion you would need the dimensions of space and time to stand in which dont exist outside the universe. Hope that helps, I haven't watched the lecture yet!
Denisasitis Avatar
Denisasitis +
Posted: 02.10.10, 06:09 PM
The observable universe is if I am not mistaken within a few hundred thousand light years of the big bang. I too wish I could wrap my mind around all this ,I do keep trying and it does come little by little. Look up the big bang, inflation and red shifting. There are some wonderful videos out there on Google , youtube and others. Cheers ,d
socratus Avatar
Posted: 12.26.09, 07:21 AM
What is the Source of the Universe ? In the book “Evolution of Physics” Einstein and Infeld wrote: “ We have the laws, but we are not aware what the body of reference system they belong to, and all our physical construction appears erected on sand ”. They are right. Why? Because : The Universe ( as a whole ) is Two- Measured, there are two Worlds: Vacuum and Gravity. What was before Vacuum or Gravity ? Does Gravity exist in Vacuum or vice versa? No answer. == . Fact and Speculation. 1. Fact. The detected material mass of the matter in the Universe is so small (the average density of all substance in the Universe is approximately p=10^-30 g/sm^3) that it cannot ‘close’ the Universe into sphere and therefore our Universe as whole is ‘open’, endless Vacuum. But what to do with the infinite Universe the physicists don't know. The concept of infinite/ eternal means nothing to a scientists. They do not understand how they could draw any real, concrete conclusions from this characteristic. A notions of ‘more, less, equally, similar ’ could not be conformed to a word infinity or eternity. The Infinity / Eternity is something, that has no borders, has no discontinuity; it could not be compared to anything. Considering so, scientists came to conclusion that the infinity/eternity defies to a physical and mathematical definition and cannot be considered in real processes. Therefore they have proclaimed the strict requirement (on a level of censor of the law): « If we want that the theory would be correct, the infinity/eternity should be eliminated » . Thus they direct all their mathematical abilities, all intellectual energy to the elimination of infinity. Therefore they invented an abstract ‘dark matter and dark energy’. They say: ‘ 90% or more of the matter in the Universe is unseen.’ And nobody knows what it is. 2. Speculation. Unknown ‘dark matter ‘ it is matter which makes up the difference between observed mass of a galaxies and calculated mass…… which….will …’close ‘ ….the Universe into sphere, as ……. as……the astrophysicists want. Question: How can the 99% of the Hidden ( dark ) matter in the Universe create the 1% of the Visible matter ? ========================== . . # Now it is considered that Newton / Einstein's laws of gravitation are basis of physics, the first laws of Universe. But the detected material mass of the matter in the Universe is so small that gravitation field, as whole, doesn't work in the Universe. So, the Newton / Einstein's laws of gravitation are correct only in the small and local part of Universe and we cannot take them as the first ones. What can the first law of the Universe be? All galaxies , all gravitation fields exist in Vacuum (T=0K). Gravitational effects took place only in a small area of Infinite Vacuum. It is impossible to use GRT to the Universe as a whole. Vacuum is “ The first law of the Universe.” The Physics first of all is Aether / Vacuum. Vacuum is the Source of the Universe . Vacuum is the Absolute Reference Frame. Without Eternal and Infinite Vacuum Physics makes no sense. ========== . .
Posted: 11.20.09, 09:37 AM
I am in love with Dr. Cobb! Anybody knows if she is single Excellent lecture. But... like "nightlight" says here: the question of "universe" is still a bit confusing. Of course, we do not have definitive answers. The scientific perspective needs to be explained in a more clear & fluid way.
dfwsupergeek Avatar
Posted: 11.11.09, 10:32 PM
I found this lecture to be fascinating- explained very well and presented some information that I didn't know before. I would watch/listen again, and I think that Dr. Cobb is my new Astronomy Crush! (blushing smiley here..)
nightlight Avatar
Posted: 10.12.09, 09:44 PM
If the universe is everything then how can it be expanding. I understand the concept of observable universe, which is that we can see, in the realm of time and space and the speed of light, but I agree with you, the universe is all, but if that is the case then how can some be considering alternate universes. Of course, this is a excercise in mind numbing that, I for one, can not get my head around and not sure I really want to.
btjones78 Avatar
Posted: 10.11.09, 11:28 PM
I think the universe is actually everything in reality. And if there is something beyond our sphere of observation, then it is included as part of the universe. The expanding "sphere" that we can see is sometimes referred to the observable universe. They may as well be one and the same because we will never be able to know for sure whether there is something beyond what we can observe.
nightlight Avatar
Posted: 10.09.09, 04:19 PM
Great lecture but I'm still a bit confused as to what exactly is the universe. As I understand it the universe is infinite and expanding but that implies that it has a parameter and what is it expanding into and is that nothing which our universe is expanding into also the universe or is the universe that which consist of the mater and energy that we know of and since it is expanding into a area of nothing that is not cinsidered the universe until the universe we know expands into it and thus becomes part of the universe?

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