On Tuesday, July 31, Dr. Robert A. Knop, Jr. came to the Galaxy Dome in Second Life to give a brief presentation about the accelerating expansion of the universe, followed by a discussion. Knop was on one of the two teams who discovered the acceleration. Those teams shared the 2007 Gruber Cosmology Prize.

You can read the text and see the slides from his presentation on his blog. Below is a transcript of the fascinating discusison that followed…

(More text follows the break…)

Note: Transcript is lightly edited. Everyone quoted gave permission, except for six people, and their names have been anonymized. All times are Pacific Daylight Time (PDT). I’m Troy McLuhan in Second Life (SL) and Rob Knop is Prospero Frobozz.

[10:24] Prospero Frobozz: At any rate, I’ll stop there — that’s the whirlwind tour of just how one goes about measuring the expansion history of the Universe.
[10:24] Prospero Frobozz: For the rest of the time we have, I’d be happy to answer questions about any of this, or about the discovery.

At this point, Second Life crashed for everyone. It then came back to life and I managed to get back in…

[11:17] Prospero Frobozz: Hey Troy
[11:17] Troy McLuhan: Hi
[11:17] Troy McLuhan: The login screen still says the grid is offline LOL
[11:17] Areyn Laurasia: Welcome back :)
[11:17] Prospero Frobozz: I’m willing to hang out and answer questions, but given that we lost most of the audience, it might be worth having a Q&A session in the next few days to pick it up?
[11:17] Joshua Linden pokes the login page.
[11:18] Joshua Linden: Login page should clear out in a minute or two, once a cache times out.
[11:18] Troy McLuhan: Is there a scheduled update tomorrow?
[11:18] Joshua Linden: Troy: Nope
[11:19] Troy McLuhan: I guess we could meet again tomorrow at 10:00 AM
[11:20] Prospero Frobozz: Troy, I think I can do that if you want to.
[11:21] Troy McLuhan: Did anyone here have a question for Prospero today, about his work on the universe’s expansion?
[11:22] Poeffie Messmer: I am a student physics at the university of leuven, so im interested :p
[11:22] Troy McLuhan: Prospero – Did you want to post your talk & slideson your blog?
[11:22] Prospero Frobozz: Yes, I will do that.
[11:22] Troy McLuhan: Okay great
[11:22] Troy McLuhan: KU Leuven, Poeffie?
[11:22] Poeffie Messmer: Yes
[11:22] Joshua Linden: Prospero: Based on our current data, how long until the horizon is restricted to just (1) local group, (2) single galaxy, (3) single solar system?
[11:23] Prospero Frobozz: Well, actually the horizon will never be limited to just that — the local supercluster is gravitationally bound, so it will never move out of the horizon.
[11:23] Joshua Linden: Ah, so gravity of the supercluster is stronger than expansion force of the dark energy?
[11:23] Prospero Frobozz: The size of the horizon isn’t actually shrinking — although it would be if there is “phantom” dark energy.
[11:23] Prospero Frobozz: Joshua: Yes, locally.
[11:23] Prospero Frobozz: Dark Energy dominates on the largest scales — 1 billion light years or thereabouts.
[11:23] Prospero Frobozz: (Perhaps a hundred million light years.)
[11:24] Prospero Frobozz: On scales of mere millions of light-years, the overdensity of galaxies is enough that their gravity dominates.
[11:24] Prospero Frobozz: The fundamental assumption of cosmology is that the Universe is homogenous and isotropic.
[11:24] Prospero Frobozz: However, this only applies on the largest scales. On smaller scales (galaxy supercluster and smaller sized things), it’s quite lumpy with a lot of structure.

[11:24] Poeffie Messmer: What is the solution of this lecture? Is there enough mass for a big crunch, are we going to keep expanding or do we sit on the razor edge of stability?
[11:24] Prospero Frobozz: None of the above :)
[11:25] Prospero Frobozz: In fact, the expansion of the universe is accelerating.
[11:25] Prospero Frobozz: That means that we’ll keep expanding…. but not in the way that we used to thinnk.
[11:25] Prospero Frobozz: The overall energy density of the Universe is the critical density — or at least very close to that.
[11:25] Prospero Frobozz: In times past, this is what would have put us on the razor’s edge of stability.
[11:25] Prospero Frobozz: However, that would be if the energy density of the Universe were made up of normal and dark matter.
[11:26] Poeffie Messmer: Ah
[11:26] Prospero Frobozz: In fact, 2/3 oir 3/4 of it is dark energy, which has a negative gravitational effect… so even though we have the “razor’s edge” density, the expansion is running away.
[11:26] Troy McLuhan: Would it be wrong to call the effect anti-gravity?
[11:26] Universa Vanalten: Sorry if you said this before but is dark energy the same as antimatter?
[11:26] Prospero Frobozz: That’s a hard question :)
[11:26] Prospero Frobozz: No, dark energy is very different from antimatter.
[11:26] Prospero Frobozz: Antimatter has normal gravity.
[11:26] Poeffie Messmer: But this acceleration means one of the possibilities will be chosen faster (unless we are stable)
[11:26] Prospero Frobozz: I would say that dark energy has a negative gravitational effect; in that sense, it’s antigravity.
[11:27] Universa Vanalten: hmmmmm
[11:27] Prospero Frobozz: However, it fits completely naturally within Einstein’s Relativity.
[11:27] Troy McLuhan: I guess that there might be “normal” and “anti” forms of dark energy?
[11:27] Prospero Frobozz: And, unless we really don’t understand it, it would be impossible to concetrate it to make antigravity flying plates or some such.
[11:27] Prospero Frobozz: Who knows :)
[11:27] Prospero Frobozz: We don’t know enough about dark energy to know that.
[11:27] Prospero Frobozz: There are examples of particles that are their own antiparticle — the photon , for example.
[11:27] Prospero Frobozz: There is no antiphoton.
[11:28] Poeffie Messmer: Shouldnt there be a fourth form of element then? normal matter, dark energy, antimatter, antidark energy?
[11:28] Poeffie Messmer: Oh, thats what Troy asked
[11:28] Anonymous Zero: What can u tell about the Black Energy?
[11:28] Prospero Frobozz: At the moment, we know very little about Dark Energy.
[11:28] Prospero Frobozz: What we know is that it makes up about 2/3 of the Universe, and that it has a negative gravitational effect. To do this, it must have a negative pressure.
[11:29] Prospero Frobozz: (Which is a bizarre concept, really, and hard to explain briefly.)
[11:29] Universa Vanalten: Or antimatter for that [anti] matter i think lol
[11:29] Prospero Frobozz: (I’m not even sure I’ve fully internalized it!)
[11:29] Prospero Frobozz: We know that Dark Energy behaves very close to something called ‘vacuum energy’ , and many people suspect that dark energy will turn out to be vacuum energy.
[11:29] Prospero Frobozz: Vaccum energy is something that is just a property of the vacuum — a constant density of energy that you have when you take everything out of a volume that you can take out.
[11:29] Anonymous Zero: Is Dark Energy like the cosmological constant?
[11:30] Prospero Frobozz: Yes — the Cosmological Constant is effectively a vacuum energy density.
[11:30] Prospero Frobozz: So, cosmological constant is a subset of dark energy.
[11:30] Prospero Frobozz: There are other things that can be dark energy that aren’t strictly a cosmological constant.
[11:30] Poeffie Messmer: Doesn’t antimatter have a negative gravitational effect? If you use forces attracting each other, the ‘negative’ matter also has a negative force on other matter
[11:30] Prospero Frobozz: Indeed, I don’t think the term “Dark Energy” was coined in 1998 when we all announced the discovery of the accelerating Universe.
[11:30] Prospero Frobozz: At that time, we were fitting the matter density and the cosmological constant.
[11:30] Prospero Frobozz: We also explored “quintessence,” a basic form of what we now call Dark Energy.
[11:31] Anonymous Zero: Is the quantum vacuum like Dark Energy?
[11:32] Prospero Frobozz: Yes, probably. Again, all of this isn’t understood as well as we’d like it to be, but the idea of the quantum vacuum — lots of virtual particle/antiparticle pairs creating and destroying themselves — could be the source of the vacuum energy density that we’ve observed as Dark Energy.
[11:32] Prospero Frobozz: Our fundamental particle theories at the moment, though, don’t allow us to meaningfully predict exactly what the quantum vacuum should be like.
[11:32] Prospero Frobozz: So, it’s an open question and an active area of research :)
[11:32] Anonymous Zero: Ok
[11:33] Anonymous Zero: Thanks so much
[11:33] Zen Zeddmore: In that the conclusion of accelerating expansion is based on the distance vs CRS values, would time dilations offer an alternate explanation for the observed data?
[11:33] Prospero Frobozz: Well, we do see a time dilation in the supernova lightcurves, that completely matches the predictions from General Relativity.
[11:34] Prospero Frobozz: GR [General Relativity] applied to the Universe tells us that if we observe something at a high redshift, time should be stretched out according to that redshift.
[11:34] Zen Zeddmore: I’m speaking of spatial time dilations .
[11:34] Prospero Frobozz: Indeed, if you look at the time it takes for a supernova lightcurve to rise and fall — that is, for it to go from explosion to maximum brightness, and then decay — it matches exactly what we expect.
[11:34] Prospero Frobozz: I don’t know what you mean by spatial time dilations.
[11:35] Zen Zeddmore: That as the density of the universe decreases. the effect on time changes.
[11:36] Prospero Frobozz: Well, in a sense, that’s sort of what the Cosmological Time Dilation is. It’s not directly tied to density, but it is tied to the expansion of the Universe.
[11:36] Zen Zeddmore: Ok
[11:36] Prospero Frobozz: If you wanted density to affect the flow of time directly, not through the expansion of the Universe you’d have to throw out a lot of General Relativity — and you’d be in a pickle trying to come up with something not horribly contrived that explained everything that GR explains right now.
[11:37] Zen Zeddmore: That time slows near a gravity well?
[11:37] Prospero Frobozz: Yes, time does slow down near a gravity well, in comparison to something farther out.
[11:37] Prospero Frobozz: Although, you have to compare it to something to be meaningful.
[11:38] Prospero Frobozz: However, the density of the Universe is such that this is a tiny effect.
[11:38] Prospero Frobozz: These time dilations have been observed on Earth — by things like the GPS satellites , where tremendous precision is needed.

Artist’s conception of a GPS satellite (NASA image)

[11:38] Prospero Frobozz: I don’t remember the numbers, but the time dilation between Earth’s surface and the orbit of the GPS satellites is something like one part in a billion.
[11:39] Zen Zeddmore: Tiny relative to our intimate use of time or tiny relative to the changes spoken of in the data of this topic?
[11:39] Prospero Frobozz: Both
[11:39] Prospero Frobozz: The kind of time dilation we’ve seen from the cosmological redshift is as much as a factor of 2.
[11:39] Zen Zeddmore: Sweet
[11:39] Prospero Frobozz: The change in density during that time would cause a gravitational redshift much less than even the Earth surface to Earth orbit change.
[11:39] Prospero Frobozz: That is, if you treated it directly as “just climbing out of a potential well.”
[11:40] Prospero Frobozz: Really, the cosmological redshift is a special case of gravitational redshift.
[11:42] Prospero Frobozz: By the way, if anybody is interested in a good book about the discovery of the accelerating Universe — both the science, and the osciology of the two groups, I recommend ‘The Runaway Universe’ by Donald Goldsmith
[11:42] Prospero Frobozz: It’s several years old now, but it was written after the 1998 discovery.
[11:42] Troy McLuhan: Wow I didn’t realize there was a book
[11:42] Prospero Frobozz: Bob Kirshner also has a book out, but I hesitate to recommend it… he’s very cruel and unfair in his treatment of his competitors (my group), and I’m not the only one to have observed that.
[11:42] Prospero Frobozz: There are a few now.
[11:42] Zen Zeddmore: Is it true our current understanding of the cosmos can’t specify if the universe is infinite in extent (that it’s galaxies all the way out)
[11:43] Prospero Frobozz: Zen — well, generally we treat it as infinite — that is, the parameters we use when we describe the Universe imply an infinite Universe.
[11:43] Prospero Frobozz: However, in reality all that we know is that it must be much bigger than what we can see.
[11:43] Joshua Linden: Anyone know if Adams and Laughlin’s ‘The Five Ages of the Universe’ is going to get an update? :)
[11:43] Prospero Frobozz: That’s a great book, by the way.
[11:43] Zen Zeddmore: This would be a most useful distinction if it could be made.
[11:44] Prospero Frobozz: It was written just before the discovery of the accelerating Universe.
[11:44] Prospero Frobozz: The accelerating Universe does change some things, because we will be limited in the number of other things we have to interact with — only local superclusters will stay bound to each other.
[11:44] Troy McLuhan: The neighbors are moving out, as it were
[11:44] Prospero Frobozz: Exacty.
[11:45] Anonymous Zero: It changed the ages of Universe?
[11:45] Prospero Frobozz: Not the next-door neighbors, but the next-block-over Universe.
[11:45] Prospero Frobozz: “The Five Ages of the Universe” is a book that looks forward to the very-distant future, and explores what the Universe will be like.
[11:45] Prospero Frobozz: It is true that the discovery of the acceleration changed our best estimate for the age of the Universe.
[11:45] Prospero Frobozz: Before that discovery, we had the embarrassing contradiction that our cosmologically derived estimates for the age of the Universe were less than the ages of the oldest stars.
[11:46] Prospero Frobozz: For a given current expansion rate, however, it turns out that if the expansion is accelerating, we estimate an older Universe.
[11:46] Prospero Frobozz: In between a few different lines of reasoning, we now have an estimate for the age of the Universe that is good to about 5%… although that’s not really the full “age” of the Universe, but the age since the parts that we kind of understand.
[11:46] Prospero Frobozz: What happened before that time we really don’t know, because our Physics breaks down.
[11:47] Anonymous Zero: Ok
[11:47] Zen Zeddmore: Has there been enough discussion about how to make the determination of weather the universe is infinite in extent?
[11:47] Prospero Frobozz: Zen — a lot of people have looked at that in a number of different ways.
[11:47] Prospero Frobozz: One way it can be finite or infinite is through its geometry.
[11:48] Prospero Frobozz: If the total density of the Universe were greater than the critical density, then we’d have a finite Universe.
[11:48] Prospero Frobozz: The spatial geometry would be something like the three-dimensional equivalent of the surface of a sphere. (The surface of a sphere is 2d)

[11:48] Prospero Frobozz: However, it looks like we don’t have enough density for that.
[11:48] Prospero Frobozz: It’s still possible to have a Universe that’s not infinite because of topology.
[11:49] Prospero Frobozz: The Universe could be something like the old “Asteroids” video game— not curved like the surface of a sphere, but still if you go off one “edge” you just come back on the other “edge”.
[11:49] Prospero Frobozz: People have looked for signatures of this in the Cosmic Microwave Background, and not seen them.
[11:49] Prospero Frobozz: So, it there is something topologically strange like that going on, it’s on scales much larger than the size of everything we can see.
[11:49] Zen Zeddmore: Or smaller : )
[11:50] Prospero Frobozz: If it was smaller, we’d have seen it.
[11:50] Troy McLuhan: I think asteroids was topologically like the surface of a donut

[11:50] Zen Zeddmore: Strings?
[11:50] Prospero Frobozz: Troy, yes.
[11:50] Prospero Frobozz: Strings may tie into all of this, but we’re not really sure because there’s not a working string theory that we can use to make lots of physical predictions.
[11:51] Prospero Frobozz: It’s counter-intuitive, but you can have the surface of a donut be not curved if you draw the lines on it right.
[11:51] Prospero Frobozz: Although I’m having trouble mentally convincing myself of that right now :)
[11:52] Troy McLuhan: Homer Simpson would be impressed
[11:52] Prospero Frobozz: Indeed!
[11:52] Zen Zeddmore: A spiral around it?
[11:52] Prospero Frobozz: Effectively, all you have to do is take a rectangle, and then identify the top and bottom edges, and identify the left and right edges.
[11:52] Prospero Frobozz: Topologically, that’s the same as a donut at that point.
[11:52] Troy McLuhan: Glue the edges together
[11:53] Prospero Frobozz: Geometry and topology can each vary independent of the other….
[11:53] Prospero Frobozz: But topology is something I really don’t know a lot about.
[11:54] Troy McLuhan: So many open questions still!
[11:54] Prospero Frobozz: That’s part of the fun! :)
[11:54] Prospero Frobozz: It would be so boring if everything were answered.
[11:54] Prospero Frobozz: That was one of the neatest things about this project.
[11:54] Troy McLuhan: Yes, but when I was a kid I thought all the adults had it figured out. What a disappointment!
[11:54] Prospero Frobozz: In 1997, Science Magazine named “Dolly the Sheep” as the breakthrough of the year.
[11:54] Zen Zeddmore: I could stand for fewer health and biology questions needing answers.
[11:54] Prospero Frobozz: They listed six or seven “projects to watch” for the next year; one of them was ours, which made us all proud.
[11:55] Prospero Frobozz: At the time, we were hoping to measure the mass density of the Universe, so that we would know how fast it was decelerating; we were checking for the Cosmological Constant, but didn’t really expect it.
[11:55] Prospero Frobozz: So, even then it was a pretty high profile project.
[11:55] Prospero Frobozz: It was a big outstanding question for decades in cosmology.
[11:56] Prospero Frobozz: That we found something much cooler and unexpected opened up a whole host of new questions in both cosmology and particle physics, and was much more exciting than “just” measuring the density would have been.
[11:56] Prospero Frobozz: Science Magazine named the accelerating Universe the “Breakthrough of the Year” in 1998 :)
[11:57] Prospero Frobozz: Although, thinking back, internally we may have been aware that our data was pointing towards a positive Cosmological Constant by the time we read the 1997 Science article.
[11:57] Prospero Frobozz: But we hadn’t announced anything yet.
[11:57] Prospero Frobozz: And at the time, I probably didn’t believe it, because I was still working on the supernova lightcurve data and thought it would all go away when I finished all the corrections and cross-checks :)
[11:58] Zen Zeddmore: You’re talking about the decay rate of the nova events?
[11:58] Prospero Frobozz: That and all sorts of other tings.
[11:58] Prospero Frobozz: I mean, heck, it’s always possible that something prosaic got mucked up in the data analysis; you need to check all that kind of stuff.
[11:59] Troy McLuhan: Have there been other indications from different methods?
[11:59] Prospero Frobozz: Yes.
[11:59] Prospero Frobozz: The supernova stuff is still the strongest direct measurement.

Remnant of Kepler’s Supernova (NASA image)

[11:59] Prospero Frobozz: However, the cosmic microwave background shows signs of it.
[12:00] ToolsRMe Shan: “Cosmic microwave background shows signs of it.” Was that evidence found by COBE?

(NASA image)

[12:00] Prospero Frobozz: Also, if you put measurements of galaxy clustering over the history of the Universe together with the strongest predictions from the Cosmic Microwave Background, you come up with a conclusion that there is Dark Energy even without the Supernova.
[12:00] Prospero Frobozz: Not COBE, but WMAP , as well as the balloon borne satellites before that.
[12:00] Zen Zeddmore: Does the CMB [Cosmic Microwave Background radiation] present us with a universal reference frame?
[12:00] Prospero Frobozz: Refinements of what COBE measured.
[12:00] Prospero Frobozz: Zen: Sort of.
[12:01] Prospero Frobozz: In that the Earth presents us with a universal reference frame that’s useful for us here.
[12:01] Zen Zeddmore: talk about throwing out Einstein.
[12:01] Prospero Frobozz: The CMB is a reference frame that all of us in the Universe could agree is a nice and convenient one to use, but it does not throw out Einstein at all.
[12:01] Prospero Frobozz: The deal with special relativity is that the laws of physics are the same in all reference frames.
[12:01] Troy McLuhan: I prefer the reference frame attached to my left ear
[12:01] Prospero Frobozz: That there happens to be this one frame that has the CMB in it doesn’t make it really all that special.
[12:02] Prospero Frobozz: Troy, that frame is a perfectly fine one, but it’s really hard to use because it’s usually not inertial :)
[12:02] Zen Zeddmore: Ok
[12:02] Troy McLuhan: That’s okay, I have equations for motion in my non-inertial reference frame
[12:02] Prospero Frobozz: F = m a + (beer)
[12:02] Troy McLuhan: Haha
[12:03] Prospero Frobozz: Plus, you know what they say about inner ear fluid and motion sickness….
[12:03] Zen Zeddmore: E=mc^2^ x zero (the day after)
[12:03] Prospero Frobozz: I probably need to take off in a few minutes….
[12:03] Troy McLuhan: Okay
[12:03] Prospero Frobozz: But I can pick this up again tomorrow at 10AM SLT.
[12:03] Troy McLuhan: Okay I’ll put out an announcement
[12:03] Prospero Frobozz: I’ll post the talk transcript and slides on my blog and mail you the URL, Troy.

Note: Click here to visit that URL.

[12:03] Troy McLuhan: Thanks
[12:04] ToolsRMe Shan: “It’s usually not inertial”. Because it is, by definition, accelerating?
[12:04] Prospero Frobozz: ToolsRMe, yes, exactly.
[12:04] Joshua Linden: Thanks a bunch! And my apologies for the “excitement”
[12:04] Anonymous Zero: Thanks very much
[12:04] Prospero Frobozz: Joshua, thanks :) And, hey, the excitement is all part of the background :)
[12:04] ToolsRMe Shan: Thank you!
[12:04] Universa Vanalten: looking forward to reviewing the blog..thanks!!
[12:05] Prospero Frobozz: Anyway, I will see you tomorrow — and e-mail you before that.
[12:05] Troy McLuhan: Okay, great thanks
[12:06] Bill Friis: Thanks.
[12:06] ToolsRMe Shan: That you, kind and wise, sir!
[12:06] Zen Zeddmore: TY, great talk.
[12:06] Anonymous Zero: Ok thx
[12:06] Prospero Frobozz waves generally

Wednesday, August 1, 2007:

[9:59] Troy McLuhan: I guess I can give some background while everyone arrives
[10:00] Troy McLuhan: Prospero Frobozz here is Dr. Rob Knop
[10:00] Prospero Frobozz waves
[10:00] St3f8n Woodget: Hello Dr. Knop.
[10:00] Troy McLuhan: He was one of the guys who discovered that the universe is expanding faster and faster over time, which was a really surprising result
[10:01] Troy McLuhan: He knows lots about astronomy and cosmology
[10:01] Troy McLuhan: Yesterday he gave a short presentation about the discovery and how it was done
[10:01] Troy McLuhan: Then SL crashed
[10:01] St3f8n Woodget: Couldn’t handle the gravity of the situation.
[10:01] Dagny Franciosa chuckles
[10:01] Prospero Frobozz: Exactly
[10:02] Troy McLuhan: It was quite bizarre. It happened exactly when he was done. Almost as if he had some connection to Linden Lab….

Note: Linden Lab is the company that created Second Life.

[10:03] Prospero Frobozz: Despite rumors to the contrary, I did not crash the grid just to get out of answering questions :)
[10:03] Prospero Frobozz: (I had other reasons too.)
[10:03] St3f8n Woodget: Running late for lunch, for one.
[10:03] Prospero Frobozz: If anybody is interested, a transcript of what I said at the introductory talk yesterday is online here
[10:03] Morrhys Graysmark smiles.
[10:04] Prospero Frobozz: Today, I’m happy to take any questions anybody has, and I’ll answer ‘em if I can.
[10:04] bluefog001 Ling: Is it time to ask questions?
[10:04] Troy McLuhan: Yes go ahead
[10:04] bluefog001 Ling: Ok troy
[10:04] St3f8n Woodget: How far along are we in figuring out what dark matter is?
[10:04] bluefog001 Ling: The universe is expanding in what?
[10:05] Prospero Frobozz: St3f8n: Pretty far, or nowhere, depending on your point of view :)
[10:05] Ms Kitty: Ouch
[10:05] Prospero Frobozz: There is a lot that we know. We have very strong confirmation that dark matter is in fact real.
[10:05] Prospero Frobozz: It’s not just a pointer to an imperfect understanding of Physics, but really some stuff that’s out there.
[10:05] Nova Susanti: Has anyone done any math on the red shift of the galaxy expansion?
[10:05] Prospero Frobozz: We know that dark matter is not made up of “normal” stuff — protons, neutrons, and electrons — but that it has to be something new.
[10:05] Prospero Frobozz: We don’t know what that new thing is.
[10:06] Prospero Frobozz: It’s possible that we’ll produce dark matter particles at the LHC, the Large Hadron Collider that’s coming online in Switzerland soon.
[10:06] Ms Kitty: raises hand
[10:06] St3f8n Woodget: When the LHC goes online, perhaps that’ll shed some light on it.
[10:06] Prospero Frobozz: Ms Kitty: Go ahead
[10:06] Pete Freenote: Have you ever heard of the “electric universe theory” and does it compliment your findings?
[10:07] Prospero Frobozz: Pete: I’ve heard of the electric universe theory — it’s one of the classic “crank” thoeries on cosmology :) All bunk, I fear.
[10:07] Ms Kitty: From what I heard yesterday, the universe is expanding then will contract upon itself
[10:07] Ms Kitty: How long do we have till we need to worry:)
[10:07] Helen Lustre: Prospero Frobozz, how has ‘established’ science gotten away with a concept like Inflation? No real explanation how it happened, just that it HAD to happen.
[10:07] Prospero Frobozz: Ms Kitty — no, that’s not quite right. That was one possibility, but now it doesn’t look like that’s going to happen. As of the 1998 data, it really looks like the Universe will expand forever.
[10:08] Prospero Frobozz: Helen Lustre — the story behind inflation really isn’t all that different from the story behind dark matter.
[10:08] Prospero Frobozz: Dark Matter was originally postulated because looking at the dynamics of galaxies and galaxy clusters, things were moving too fast for the gravity of the things we could see.
[10:08] Nova Susanti: I’m not convinced the universe is expanding
[10:08] Helen Lustre: Is that your answer to my question?
[10:08] Prospero Frobozz: Part of the answer, still going.
[10:08] Ms Kitty: But if it continues to expand Doctor… won’t the earth move further from its life source the sun and then we will be in trouble
[10:09] Prospero Frobozz: Still on inflation : Dark Matter was introduced as a paradigm to explain some of the observations. Even today, though, we don’t have an explanation for what it is — we have possibilities, but no explanation. But it explains so much that we believe it is real.
[10:09] Nova Susanti: The only evidence for expansion is red shift
[10:09] Prospero Frobozz: Similarly, inflation is a paradigm that explains a number of observations we make about the Universe, including some observations in detail in the fluctuations of the Cosmic Microwave Background.
[10:09] Nova Susanti: I postulate thet red shift as seen by us is a gravitational anomally
[10:10] Prospero Frobozz: We don’t know what causede it, but the data do point towards inflation having happened.
[10:10] Petlove Petshop: And don’t there have to be limits to have expansion in the first place?
[10:10] Prospero Frobozz: Helen, so that’s the answer — it’s got all sorts of outstanding questions, it may turn out not to be right, but it’s the paradigm right now because it explains a number of things.
[10:10] Ms Kitty: How fast is it inflating?

Note: Ms Kitty probably meant “expanding” rather than “inflating”. In cosmology, “inflation” and “expansion” have two very different meanings – Inflation was a rapid growth of the universe that apparently happened when the universe was very young, whereas expansion is something that continues to this day.

[10:10] Prospero Frobozz: Re: the expansion of the Universe: Galaxies are moving farther apart from each other, but they are not expanding themselves.
[10:10] Prospero Frobozz: Similarly, the Earth is not moving away from the Sun as a result of the Universe’s expansion.
[10:10] Ms Kitty: Hmmmm
[10:11] Prospero Frobozz: The gravity of galaxies themselves holds them together against the expansion.
[10:11] Ms Kitty: Interesting
[10:11] Prospero Frobozz: It’s similar to the Earth orbiting the Sun; the natural action of the Sun’s gravity would be to stretch the Earth out into a long stream of material, as the parts of the Earth closer to the Sun want to orbit faster than the parts farther awa. However, the Earth is held together by its own gravity.
[10:11] Anonymous Two: Isn’t that a counter proof against the expansion though?
[10:11] Prospero Frobozz: Anonymous Two: Isn’t what?
[10:12] Anonymous One: Quick question: Could it be possible that matter itself is shinking faster than the universe, making us believe it is expanding when it’s not?
[10:12] Anonymous Two: The fact that galaxies themselves are not expanding
[10:12] Barley Oh: How is it possible to detect dark matter in a collider?
[10:12] Helen Lustre: I think you misunderstood “inflation.” I meant the Inflationary Period at the origin of our universe. My fault for not being precise.
[10:12] Anonymous Two: Gravity may not be the explanation, maybe no expansion is the explanation
[10:12] Prospero Frobozz: Anonymous One: Dunno :) That would be a pretty wacky metric, and I suppose you might be able to make it work, but it would probably be a lot more convoluted than the explanation we hvae.
[10:12] Prospero Frobozz: Helen, yes, that’s the inflation I was talking about.
[10:13] Prospero Frobozz: Barley Oh: How do we make dark matter in a collider? The answer would be if dark matter particles are massive enough (on particle scales) that we haven’t had high enough energies yet to make them. The newest collider is going to test this idea called ‘supersymmetry’ , which postulates a whole new class of particles.
[10:13] Prospero Frobozz: If they exist, the lightest one might be the dark matter particle.
[10:13] Prospero Frobozz: We don’t know yet, of course! That’s why we’re doing the experiment.
[10:14] Very Susanti: Why do you say galaxies are not expanding? The key thing is not that universe is expanding but also the rate of expansion is increasing right so galxies will continue to expand ever be so slighty
[10:14] Barley Oh: TY
[10:14] Barley Oh: Oh lol I thought something new!
[10:14] Prospero Frobozz: Very Susanti : galaxies are not expanding because their own gravitational forces are locally much stronger than the expansion.
[10:15] Prospero Frobozz: Think of paper clips on a rubber band.
[10:15] Prospero Frobozz: If you stretch the rubber band out, the paper clips get farther apart, but they don’t expand themselves.
[10:15] Very Susanti: They don’t collapse but the size increases due to the expansion
[10:15] Very Susanti: That is what I meant
[10:15] Prospero Frobozz: The rubber band does pull one side of the paperclip away from the other side, but the paper clip is held together much more strongly by it’s own structure.
[10:16] Pete Freenote: How does the expansion affect us? does it speed up time?
[10:16] Very Susanti: Ok sure
[10:16] Prospero Frobozz: Very Susanti: Galaxies are in an equilibrium themselves. It’s not the expansion of the Universe that keeps them from collapsing under their own gravity, it’s their rotation and internal motions.
[10:16] Very Susanti: But as the rate continues to expand the galaxies may become rarified
[10:16] Prospero Frobozz: Pete Freenote: It doesn’t affect us very much, in fact :)
[10:16] Prospero Frobozz: Very Susanti: They will be come more rarified in that they will all be farther apart, but any changes in their internal structure will be largely independent of the expansion of the Universe.
[10:17] Prospero Frobozz: Just as the internal structure of a tree growing on Earth is independent of the Sun’s motion around the center of the Galaxy.
[10:17] Very Susanti: In a critically damped universe is that statement true forever?
[10:17] Anonymous Two: Can’t it be calculated how much gravity would make the galaxies collapse and how much expansion affects that?
[10:18] Prospero Frobozz: Anonymous Two: yes, and the expansion is a tiny effect compared to the gravitational forces within the galaxy, and compared to the effect of the motions of the stars and dark matter.
[10:18] ToolsRMe Shan: So as trhe galaxies move further and faster apart, at some point they will exceed the speed of light. At some point in the distant future, our galaxy will be alone. Is that current theory still?
[10:18] Prospero Frobozz: ToolsRMe Shan: sort of.
[10:18] Anonymous Two: So you’re saying the calculation cannot be accurate?
[10:18] Petlove Petshop: Perhaps there’s a more metaphysical explanation for the nature of what we perceive as the universe… we may not see what we think we see, on many levels
[10:18] Prospero Frobozz: In fact, it’s not just our galaxy, but the local supercluster of galaxies that are still bound together.
[10:18] Prospero Frobozz: So we’ll stay together with our nearest neighbors.
[10:18] Quanta Torok: What prospect does expansion hold for intelligent species? Are we just going to end up on an island in the middle of nowhere?
[10:18] Prospero Frobozz: But other than that, yes, as the expansion of the Universe gets faster and faster, eventually there will be this lonely isolated group of galaxies that’s all we can see.
[10:19] Prospero Frobozz: Quanta: Yes, pretty much :) Except that it’s a big island. Our galaxy alone has a hundred billion stars.

Our Milky Way Galaxy, as seen from within (NASA image)

[10:19] ToolsRMe Shan: Until some future Frobozz postulates a Darker Energy
[10:19] Prospero Frobozz: But the ultimate fate of the Unvierse is a cold, lonely, isolated place…. waaaaaaah!
[10:19] Anonymous Three: That mean the universe is getting more cold everyday ?
[10:19] Prospero Frobozz: Anonymous Three: yes.
[10:20] Prospero Frobozz: In a sense.
[10:20] Prospero Frobozz: Of course, bits of the Universe are getting hotter, but overall it’s getting colder.
[10:20] Nova Susanti: So entropy cannot be reversed?
[10:20] Prospero Frobozz: Nova Susanti: No, entropy can’t be reversed.
[10:20] Quanta Torok: How can the universe be getting colder? Where is the energy going?
[10:20] Petlove Petshop: It has no opposite, entropy?
[10:20] Petlove Petshop: No rebound?
[10:20] Nova Susanti: I’ll build a gravity machine and draw everything back together
[10:20] Prospero Frobozz: Quanta Torok: Heh, that’s a hard question. It turns out that in General Relativity, there is no global conservation of energy law….
[10:21] Prospero Frobozz: There is a local conservation of energy law that states, roughly, that within any finite bounded volume, the rate of change of energy in that volume equals the rate at which energy flows through the boundaries of that volume.
[10:21] Prospero Frobozz: But it’s not really meaningful to talk about the energy of the “whole Unvierse” in General Relativity, it turns out.
[10:21] Ka Kurka: Getting colder does not mean that the energy is being lost
[10:21] Quanta Torok: Ok
[10:21] Prospero Frobozz: bluefog001: That was one possibility, but the Universe does not appear to have either that geometry or that topology.
[10:22] Troy McLuhan: How long till all we see is the local supercluster of galaxies?
[10:22] bluefog001 Ling: Ok thanks
[10:22] Prospero Frobozz: Troy: Not sure off of the top of my head, but at least tens of billions of years.
[10:22] Troy McLuhan marks his calendar
[10:22] Prospero Frobozz: Probably hundreds of billlions?
[10:23] Prospero Frobozz: I’d have to sit down and work it out. I think there was a paper by Lawrence Krauss and Bob Scherrer that worked out out; I could dig that up.
[10:23] Troy McLuhan: Yes maybe do that and post it in the blog
[10:23] Prospero Frobozz: That’ll be a blog post all it’s own, probably, if I do it :)
[10:23] Helen Lustre: What is the reason for that “non-Gaussian anamoly” in the CMB?
[10:24] Prospero Frobozz: Helen Lustre: I’m not sure. I haven’t kept up with all of the details of the CMB.
[10:24] Troy McLuhan: CMB = the Cosmic Microwave Background radiation
[10:24] Anonymous Two: Sorry, what is the blog’s url?
[10:24] Ms Kitty: :)
[10:24] Prospero Frobozz: I do know that there are unexplained things in the CMB that seem to align with the plane of the Solar System.
[10:24] Helen Lustre: The detals have been out for years. It looks like a ring tilted slightly off anlge.
[10:24] Prospero Frobozz: This to me suggests some kind of observer bias, but last I checked it hadn’t been explained.
[10:25] Prospero Frobozz: Helen: Yeah, and I think the tilt is the same as the tilt of the plane of the Solar system.
[10:25] Prospero Frobozz: Anonymous Two: my blog is at http://www.scienceblogs.com/interactions
[10:25] Anonymous Two: TY
[10:25] Helen Lustre: All four detectors on the WMAP agreed that it was truly from the CMB.
[10:25] bluefog001 Ling: A simple remark: It’s a lovely place here with a beautiful sky
[10:26] Prospero Frobozz: Helen : Yeah, I know. I’ve heard a lot of talks from cosmologists saying that they think it’s real, that zodiacal dust can’t explain it, etc. But, I’m curmudgeonly enough to think it’s mighty suspicious that it’s aligned with the plane of the Solar System.
[10:26] Helen Lustre: Hmmmmmmm…
[10:26] Prospero Frobozz: I’m pretty sure that remains unexplained, although a number of people have pointed out that it may be a violation of isotropy. (For those who don’t know, “isotropy” is the notion that the Unvierse looks the same in all direcitons, and there is no “preferred” direction.)
[10:28] Prospero Frobozz: Does anybody else have questions?
[10:28] ToolsRMe Shan: Yet a philosophical analog to isotropy would be the equivalence of matter and anti-matter. Yet there was a small difference in proportion at the beginning of the universe. Could there not be a similar analog in isotropy?
[10:28] Prospero Frobozz: If you asked questions earlier I didn’t answer, ask again; sometimes, when a few questions come in at once, I miss some.
[10:28] Prospero Frobozz: ToolsRMe: Yeah, there could be. The thing is that anisotropies tend to be smoothed out with the expansion, so it would have to be a pretty big anisotropy at “the beginning”.
[10:29] ToolsRMe Shan: A small “spin” at the beginning?
[10:29] Prospero Frobozz: Yeah, something like that.
[10:29] Quanta Torok: I remember reading about speculation that some of the constants of the universe have changed over time. Is this still held to be possible?
[10:29] Prospero Frobozz: Yes, it’s still held to be possible.
[10:30] Prospero Frobozz: There is a controversial measurement that the ‘fine structure constant’ (roughly, the strength of the electromagnetic force) has changed by a very small fraction in the last 10 billion years or so.
[10:30] Prospero Frobozz: There are some measurements that have a marginal detection, some that don’t see it.
[10:30] Morrhys Graysmark: What would happen if gravity was changing over time?
[10:30] Prospero Frobozz: It’s not something to hang your hat on at the moment.
[10:30] Prospero Frobozz: Well, there’s a number of ways gravity could be changing over time. If the Speed of Light was changing at a different rate from the Gravitational Constant, that would change gravity over time.
[10:31] Prospero Frobozz: Any plausible changes in the last 10-12 billion years are going to be very small effects, though.
[10:31] Prospero Frobozz: People have talked more seriously about a much faster speed of light in the early Universe as an alternative to inflation, but at the moment inflation looks more plausible.

Note: This is commonly called the Variable Speed of Light (VSL) concept.

[10:31] Troy McLuhan: If fundamental constants change over time, then that might be another explanation for the different brightnesses of the supernovas
[10:31] Barley Oh: raises hand
[10:31] Morrhys Graysmark: That’s my thought.
[10:31] Anonymous Two: I may have missed this, but is there an explanation for the acceleration in expansion? should it be a force and can we measure that force?
[10:31] Prospero Frobozz: “Inflation” is the notion that in the very early Unvierse (we’re talking the first billionth of a billionth of a second), the Universe expanded tremendously fast — doubling in size a hundred times or thereabouts.
[10:32] RP Heron: What about the question of ideosyncratic historical effects in determining future trajectories? Although isotropy makes alot of sense , there is the possibility of a “drunkards’ walk” pulling the system into a non-isotropic state, due to stochactic effects at a distant point in the past. Since we only have one universe to look at, how does one differentiate between different randomly acchieved outcomes?
[10:32] Prospero Frobozz: Troy: Yeah, but to get that much change, it would be odd if the spectra and lightcurves still worked as well as they did.
[10:32] Prospero Frobozz: RP Heron: That’s a possibility - “cosmic variance” is the fact that we only have one Universe to observe.
[10:33] Prospero Frobozz: The thing is, if you need some wildly improbable state, it could happen, but it begs the question: why are we in such a wildly improbable state?
[10:33] Prospero Frobozz: The kind of large spins needed to geenrate the CMB large-scale anisotropy are like that- given what we understand, it wouldn’t be that likely. Which may just mean we don’t understand everything :)
[10:33] RP Heron: Fair enough. =)
[10:34] ToolsRMe Shan: “The fact that we only have one Universe to observe” Which leaves an interesting philosophical question. If the other superclusters are no longer observable, do they exist?
[10:34] Prospero Frobozz: Anonymous Two: he explanation for the current acceleration of the Universe is “dark energy,” a substance whose gravitational effect is negative. The most likely candidate for dark energy at the moment appears to be vacuum energy, which acts the same as a Cosmological Constant (for those of you who have heard of that).
[10:34] Troy McLuhan: And if a tree falls in an unobservable supercluster…

Fallen Tree by John Weslkey Barker on Flickr Creative Commons

[10:34] Morrhys Graysmark: :)
[10:34] Prospero Frobozz: ToolsRMe: If the other superclusters are outside our horizon, do they exist? Well, they can’t affect us, but I would say that they exist.
[10:35] Prospero Frobozz: But you’re right, at some point that becomes philosophical.
[10:35] Barley Oh: Is light still considered massless?
[10:35] Prospero Frobozz: Light is massless, yes.
[10:35] Prospero Frobozz: But it does have energy — so it does generate gravity.
[10:35] Barley Oh: How’s that?
[10:35] Prospero Frobozz: The source of gravity is all energy density; mass is just one form of energy, and the conversion between the two is E=mc^2^
[10:36] Barley Oh: Yes, but who does the conversion, in the cosmos?
[10:36] Prospero Frobozz: For Newton’s gravity, we just use mass, because things are moving slow enough that the amount of gravity we have from mass overwhelms the amount of gravity we have from anything else.
[10:36] Helen Lustre: About ‘odd’ states… if our IS an odd state AND the only one that allows life that can be aware of itself, does it matter that it is a “long shot?” We think we are… therefore we are!
[10:36] Prospero Frobozz: Barley Oh: The conversion is really for our covnenience. Mass is “just another” form of energy.
[10:36] bluefog001 Ling: Light is curving next to a planet, isnt’it ?
[10:36] Barley Oh: Ok
[10:36] Prospero Frobozz: Helen Lustre: Yeah, that’s the Weak Anthropic Argument. Which I think is fine, but lots of cosmologists get all bothered about.
[10:37] Prospero Frobozz: bluefog001: Yes, the path of light will curve around a planet or star.
[10:37] Helen Lustre: Speaking about bother astromers… Are you one of the many astronomers who get upset when reminded that astronomy was the natural outgrowth of astrology, since the ancients watched the skies for clues to cyclic events?
[10:37] Prospero Frobozz: There was a period in the Universe — before a hundred thousand years old or so — when the dominant source of gravity controlling the expansion was in fact radiation (light), and not mass.
[10:37] Fos Dagger: If light creats gravity, does the light passing around a planet afect it’s trajectory in any measurable way?
[10:38] Prospero Frobozz: Helen Lustre: No, I’m not bothered by that, but I am bothered when people still think that there’s any predictive power in astrology today!
[10:38] Prospero Frobozz: Fos: Not in any measurable way :)
[10:38] Prospero Frobozz: It would take a tremendous energy density of light for that to happen, and we’d have other problems then….
[10:38] Very Susanti: Well you can predict what millions of people will read in the morning paper
[10:38] Prospero Frobozz: Very Susanti: Heh
[10:39] RP Heron: Helen: “Not only is the Universe stranger than we imagine, it is stranger than we can imagine.” – Eddington
[10:39] Helen Lustre: But, if the Sun strongly influences the Earth (it does) and the Moon influences the Earth (it does), why can’t the planets (which influence the Sun) also influence the earth, through the Sun?
[10:40] Prospero Frobozz: Well, the planets do influence the Earth — the Earth’s orbit is slightly modified, mostly by Jupiter.
[10:40] RP Heron: Absolutely
[10:40] Prospero Frobozz: But that’s very different from saying that where the Sun and planets are in the sky is going to affect the type of person you are, or the type of day you will have.
[10:40] RP Heron: Tides are heavily influenced by the near planets, directly.
[10:40] Anonymous Four: I have a question……if the universe is expanding, what exactly is it expanding into? And isn’t it possible that this area that it is expanding into is of finite space?
[10:40] Prospero Frobozz: If you are standing next to your car, the gravitational influence of your car on you is greater than the gravitational influence of Jupiter on you.
[10:41] ToolsRMe Shan: Do we have an estimate for the total mass/energy of the universe at the Big Bang … and has any of the universe gone over the “event horizon” because of expansion and/or dark energy?
[10:41] bluefog001 Ling: That was my question
[10:41] Helen Lustre: It has been documented (I’ll have to look up the quote) that the gas giants cause cycles on the Sun.
[10:41] Prospero Frobozz: ToolsRMe: The “total” mass of the Universe is tough, because we treat the Universe as infinite… so the total energy would be infinite.
[10:41] Very Susanti: Ohh what is a few infinities among friends
[10:41] Prospero Frobozz: What you could do is compare how much has gone outside the horizon over some time period to what is inside the horizon right now.
[10:41] Very Susanti: Never bother particle physicists
[10:42] Prospero Frobozz: Due the current period of acceleration, not very much has yet.
[10:42] Prospero Frobozz: During the inflationary epoch at the beginning of the Universe, many many times what’s inside the horizon went outside the horizon.
[10:42] ToolsRMe Shan: “Ohh what is a few infinities among friends” Answer: Aleph something.
[10:42] Fos Dagger: Does the Universe being infinite require that there be infinite energy in it? Or could energy be finite in an infinite space?
[10:42] Morrhys Graysmark: Why does an infinte universe mean infinite energy? Can’t the energy trail off in a way that makes it finite?
[10:42] Very Susanti: Countable infinities are all the same
[10:42] RP Heron: What is your thinking on topography of the Universe? And whether it potentially has changed after time=0
[10:43] Prospero Frobozz: Well, the way we treat the Universe is that it’s homogenous and isotropic — so the energy density is the same everywhere, which makes it infiite.
[10:43] Morrhys Graysmark: The way we treat it….
[10:43] Prospero Frobozz: If it’s finite, then space also has a geometry that causes it to “curve back on itself”, like the surface of a sphere.
[10:43] ToolsRMe Shan: “Countable infinities are all the same” Why should the energy in the universe be countable? Actually, I’m asking a serious question.
[10:43] Fos Dagger: How can an infinite area expand?
[10:43] Prospero Frobozz: So, yes, the way we treat it may not be strictly correct.
[10:44] Prospero Frobozz: But every observation, with the possible exception of the aforementioned anomaly on the CMB, supports the notion of homogeneity and isotropy — so it has to be a good assumption on scales at least several times what we know.
[10:44] Anonymous Four: Is it true that there is a crack in Uranus?
[10:44] Prospero Frobozz: Re: how an infite area can expand… it just gets bigger.
[10:44] Prospero Frobozz: The distance between any two galaxies goes up.
[10:44] Prospero Frobozz: Pick any two galaxies, anywhere, and the distance between them goes up.
[10:44] Prospero Frobozz: Anonymous Four: I have never tried to buy crack on Uranus, no.
[10:45] Transcriptionist Writer: Even if the two gallaxies are headed towards each other?
[10:45] Barley Oh: LOL prospero
[10:45] Prospero Frobozz: Well, ok, substitute “superclusters” where I said “galaxies”.
[10:45] Prospero Frobozz: Galaxies do have local motions.
[10:45] Fos Dagger: So if the Universe is homogenous, and galaxys are getting further apart, is it becoming less dense?
[10:45] Prospero Frobozz: Yes.
[10:45] Prospero Frobozz: The matter is getting less dense, anyway.
[10:46] Prospero Frobozz: If Dark Energy is vacuum energy, that density is staying constant.
[10:46] Prospero Frobozz: (Vacuum energy is wacky stuff.)
[10:47] Fos Dagger: Could Dark Energy be created/destroyed, or converted into regular energy and back?
[10:47] Prospero Frobozz: Fos: Dunno.
[10:47] Prospero Frobozz: That depends on what it is.
[10:48] Transcriptionist Writer: Can dark energy snap through a dark hole?
[10:48] Prospero Frobozz: If the inflation paradigm is right, then, yea, that happened with the dark-energy-like stuff that drove inflation in the early universe.
[10:48] Fos Dagger: Where can I buy some of this Dark Energy? :)
[10:48] Prospero Frobozz: Transcriptionist Writer: Dunno. :) Knowing what goes on with spacetime right at the core of a black hole is unknown to our Physics, because we don’t have a working theory of quantum gravity.
[10:48] Prospero Frobozz: Fos Dagger: It’s all around you :)
[10:49] RP Heron: Vacuum energy and reverse gravity make my head hurt.
[10:49] Prospero Frobozz: If you cup your hands, you’re holding something like a gram of air, 10^-23^ grams of dark matter, and 10^-29^ grams equivalent of dark energy.
[10:49] Very Susanti: What would it take to nail down the issue of dark energy? I have seen back and forths on whether it is actually required, and can it be used to set limits on quantuim gravity theories?
[10:49] Prospero Frobozz: Those numbers may not be right; I’ve calculated them, but pulled them from my head just now.
[10:49] Prospero Frobozz: Very Susanti: Hopefully dark energy can set limits on quantum gravity, but right now we don’t know enough about either to figure that out.
[10:49] Transcriptionist Writer: How do you measure dark energy?
[10:50] Prospero Frobozz: Right now, all of our measurements about dark energy come from observations of teh expansion history of the Universe.
[10:50] Transcriptionist Writer: between the clusters is dark energy?
[10:50] Prospero Frobozz: Upcoming studies of dark energy are going to measure that more carefully in order to further constrain some basic properties of it — but we’re really talking in broad terms rightnow.
[10:50] Prospero Frobozz: Dark energy is everywhere, with the same (or very close ot the same) density.
[10:50] Prospero Frobozz: Embedded in that are clusters of galaxies.
[10:51] Helen Lustre: Bye, all. Have to run off
[10:51] ToolsRMe Shan: Are there any — even theoretical — ways to harness Dark Energy for human use? Is the problem that there is no gradient for Dark Energy?
[10:51] Prospero Frobozz: ToolsRMe: No theoretical ways, even. Yeah, there seems to be no gradient, so harnessing it would be impossible.
[10:51] Very Susanti: Is there even a consensus at the moment as to whether dark energy is actually required to explain current observations?
[10:51] Prospero Frobozz: Maybe some century… :)
[10:52] Very Susanti think of Casimir engery machines
[10:52] Prospero Frobozz: Very Susanti: Sort of. People do all agree that the observations are real now. Some people are still working on the idea that our theory of gravity (General Relativity) is incomplete rather than needing to introduce a new “thing”
[10:52] Prospero Frobozz: Yeah, the Casimir effect probably is related to dark energy.
[10:53] Prospero Frobozz: I am told that even though there’s no theoretical way to harness Dark Energy, that hasn’t stopped Haliburton from obtaining a lucrative government contract to do just that.
[10:53] Prospero Frobozz: :)
[10:53] Morrhys Graysmark: LOL
[10:53] Transcriptionist Writer: lol
[10:53] Very Susanti: Yay graf
[10:53] Barley Oh: noooo! Halliburton!
[10:53] ToolsRMe Shan: Well, if there is no gradient to Dark Energy, is it then nothing more than the philosophical equivalent of the Aether?
[10:54] Prospero Frobozz: ToolsRMe: Not really — because the gravitational effect on the Universe depends not on a gradient but on the absolute energy density.
[10:54] Prospero Frobozz: It’s possible that it’s like the aether — the aether was a thing introduced to explain what we didn’t understand about E&M [Electricity and Magnetism], specifically, what are light waves “waving”, and what is the speed of light relative to?
[10:54] Kermit Halasy: Prospero, could you post the URL for your blog again?
[10:54] Prospero Frobozz: The answer to that was special relativity, and the aether got tossed out.
[10:55] Transcriptionist Writer: So dark energy has a denisity
[10:55] Prospero Frobozz: It’s possible that dark energy isn’t a “thing,” but is a pointer to our theory of gravity being incomplete.
[10:55] Prospero Frobozz: Yes, dark energy does have a density.
[10:55] Transcriptionist Writer: And what does dark energy have to do with gradient?
[10:55] Prospero Frobozz: Something like 10^-29^ grams (energy equivalent) per cupped hand volume, if my memory is right.
[10:55] Prospero Frobozz: Kermit: http://www.scienceblogs.com/interactions
[10:56] ToolsRMe Shan: Pardon, but it seems like a bookkeeping entry. Until the interactions of neutrinos with detectable matter was eperimentally confirmed, neutrinos were a bookkeeping entry. What theoretical predication can be made for the equivalent Dark Energy particles?
[10:56] Prospero Frobozz: Transcriptionist: Generally, to harness something as energy, you need a gradient: more in one spot than another.
[10:56] Prospero Frobozz: A gradient in temperature will cause heat to flow, for example.
[10:56] Prospero Frobozz: ToosRMe: Well, I wouldn’t say that neutrinos were really bookkeeping.
[10:56] Prospero Frobozz: If they were bookkeeping, then you would have been taking seriously the possibility that the local conservation of energy is violated.
[10:57] Prospero Frobozz: Which some did — but people believed that neutrinos had to be real things, and eventually that was experimentally confirmed.
[10:57] Prospero Frobozz: Hopefully, we’re approaching the same thing with Dark Matter.
[10:57] Prospero Frobozz: Dark Energy — maybe it’s bookkeeping, maybe it’s not.
[10:57] Barley Oh: Quantum theory allows for exceptions to conservation of energy
[10:57] Very Susanti: Neutrinos are real I have a pocket full of them
[10:57] Transcriptionist Writer: Dark energy is moving, expanding?
[10:57] Prospero Frobozz: Barley Oh: Only on very short timescales.
[10:58] ToolsRMe Shan: The point I was trying to make is that there were theoretical considerations that said that neutrinos would eventually be predicted to interact with some detector. Is there something similar for Dark Energy?
[10:58] Prospero Frobozz: Transcriptionist: We don’t really know anything about the dynamics of dark energy. At the moment, we know its density, and we have some limits on this thing called the “equation of state” parameter that relates its (negative) pressure to its energy density…. and that’s it.
[10:58] Prospero Frobozz: ToolsRMe: At the moment, no.
[10:58] Prospero Frobozz: Or, perhaps, there are lots; there are a million models of Dark Energy out there. But we don’t know enough to really ground most of them.
[10:59] Quanta Torok: Is dark matter more than just subatomic particles? Could it work its way up to what we consider matter?
[10:59] Prospero Frobozz: Quanta Torok: Well, when we say “matter” we’re generally talking about things made out of quarks and leptons (electrons [for example]).
[10:59] Transcriptionist Writer: do any “models” decrease?
[10:59] Prospero Frobozz: Dark Matter isn’t made out of that, so it won’t be matter in the “matter/anitmatter” sense, but it will be stuff.
[10:59] Transcriptionist Writer: show a decrease?
[11:00] Prospero Frobozz: Transcriptionst: Yes, there are some models for dark energy that have its energy density decreasing with time… some have it increasing! Those latter ones are more fun :)
[11:00] Prospero Frobozz: Quanta Torok: Almost certainly, though dark matter won’t clump except via gravity. Normal matter clumps into molecules and rockes and people and so forth. Dark matter almost certainly won’t do that.
[11:00] Transcriptionist Writer: What’s left is the action of decrease?
[11:00] Prospero Frobozz: I need to take off in a few minutes here.
[11:00] Transcriptionist Writer: okay
[11:00] Quanta Torok: No chance for dark matter aliens then.
[11:01] Prospero Frobozz: Transcriptionist Writer: Well, if it’s steadily decreasing, eventually it will decay away and we’ll be left with a coasting, not accelerating, expansion.
[11:01] Prospero Frobozz: Quanta Torok: Probably not, alas, although read “Starplex” by Robert J. Sawyer if you like the idea :)
[11:01] Transcriptionist Writer: How can I get notified of future “classes.”
[11:01] Quanta Torok: Yeah!
[11:01] Very Susanti: Well what about Hadronic dark matter?
[11:01] Prospero Frobozz: Join the Science Center group.
[11:01] Transcriptionist Writer: Okay, thanks.
[11:01] Prospero Frobozz: Very Susanti: Hadronic Dark matter is basically ruled out. Hadrons can’t make up more than something like 5% of the energy density of the Universe.
[11:02] Troy McLuhan: Yes, anyone can join the Science Center group
[11:02] Troy McLuhan: Announcements about events like this get posted to that group
[11:02] Prospero Frobozz: The hadronic limits are based on observations of the ratio of Helium to Hydrogen in the Universe, as well as some other light elements.
[11:02] Prospero Frobozz: The ratios would be very different from what was observed if all of the dark matter (about 30% of the density of the Universe) were made up of hadrons.
[11:03] Prospero Frobozz: Anyway, thank you all for coming!
[11:03] ToolsRMe Shan: Thank you!!!!
[11:03] Morrhys Graysmark: Thank you!
[11:03] Quanta Torok: Thank you!
[11:03] Kermit Halasy: /clap
[11:03] Chaim Beaumont: Thank you :)
[11:03] Transcriptionist Writer: I’m sorry I was late. It was interesing, very interesting.
[11:03] Very Susanti: Thank you
[11:03] Transcriptionist Writer: Thank you.
[11:03] Petlove Petshop: You’re a trooper prof!
[11:03] ToolsRMe Shan stands and gives ovation.
[11:03] Barley Oh: Thank you so much for your time
[11:03] Troy McLuhan: Thanks Dr. Knop!
[11:03] Chaim Beaumont: Yes there should be more of this.
[11:04] Prospero Frobozz: Have fun, y’all! And grab the freebies by the door — there’s a copy of my hat there :)
[11:04] Anonymous Five: Thankyou Prospero
[11:04] Troy McLuhan: Cool hat
[11:04] Prospero Frobozz: Thank you all, and you’re welcome all.
[11:04] Quanta Torok: Cool!
[11:04] Fos Dagger: Thank you Prospero
[11:04] Prospero Frobozz waves generally
[11:04] Chaim Beaumont: I joined 2nd life for the hope of finding some lectures. One month later on here and I do.
[11:04] Chaim Beaumont: So I’m a Happy avatar
[11:04] Chaim Beaumont: Hehe
[11:05] Troy McLuhan: Well, I guess that’s all folks
[11:05] Troy McLuhan: Stay tuned for more great discussions like this.

If you’d like to be informed of future events like this in Second Life, then join the “Second Life” group on Nature Network or join the “Science Center” group in Second Life.

Copyright© 2007 by T. Troy McConaghy.

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