Category: Physics (Page 1 of 2)

Lisa Randall: Dark Matter and the Dinosaurs

Lisa Randall signing my copy of “Dark Matter and the Dinosaurs”

Lisa Randall was at Politics and Prose Bookstore in Washington DC tonight, giving a very interesting talk about Dark matter and the Universe. In her new book, Dark Matter and the Dinosars, she ties in the dinosaurs by speculating how Dark matter may have been responsible for popping a comet out of the Oort Cloud, thus sending it on its way to crash into the Earth 65 million years ago- wiping out the dinosaurs and most life on the planet.  

Her talk was great; first book tour talk I’ve been to that was like a classroom lecture:  she had slides with diagrams, pictures and explanatory text.  So easy to follow and really engaging. 

Her book, “Dark Matter and the Dinosaurs” was just released yesterday.  Here she is signing my copy.

Lecture on The Shape of Inner Space by Shing-Tung Yau (and some DC pictures)

shape of inner space

Professor Shing-Tung Yau gave a lecture last night at the Smithsonian (Carmichael Auditorium of Museum of American History), based on his book, The Shape Of Inner Space. He basically described the trajectory of his career over the past 40 years or so, along the way describing “Calabi-Yau” space and how it relates to String theory and maybe even the real world.

The basic tenet of String Theory is that all particles, at their most basic level, are made of vibrating bits of tiny strings. Yes, strings. The way they vibrate basically dictates which particles they manifest as. I won’t even pretend to know the math involved. One non-intuitive (to me as a non-mathematician, anyway) upshot of the string theory math is that it requires (reveals?) a total of 10 dimensions – 6 more than the 4 with which we are most familiar (3 dimensions of space plus time). Turns out according to theory that the extra 6 dimensions are hidden away in Calabi-Yau Space. This invisible space exists at every point in “real” space.

At this point, Prof. Yau asked, “Who cares?”. Well, it turns out the exact shape/geometry of this “Calabi-Yau Space” dictates the properties of our universe and the kind of physics we see.

The lecture was sold out…

Keep reading to see how Yau’s discussion of Mirror Symmetry (spaces) can be related to eating at a British-themed pub…

After the lecture I managed to take some pictures of Washington, D.C. in the evening light. I had a half-mile hike back to the Metro anyway, as I used the Archives stop on the Green line. This involved no train changes, and the weather was just perfect for a walk downtown. It’s actually very relaxed in the evening, as most people have gone home for the day. The downside is that it can be a bit hard to find someplace to eat around the Smithsonian in the late evening. I asked a security guard who happened to be taking a break, and he pointed me to the Elephant and Castle Pub on Pennsylvania Ave. Ok, his exact words were more like, “not much open right now except super-fancy places- just that sports bar over there…”. That was not really what I was looking for, but I was going that way anyway and I had missed dinner, so I stopped in. Glad I did! Got a nice table outside (did I mention perfect weather) and had some Fish and Chips and a London Porter. Yum! Not too pricey, and the fish was delicious – just lightly breaded/ fried crispy and golden. The porter was delicious too- chocolately and coffee undertones.

Mirror Universe? I was quite intrigued by something the waitress said when she brought me my fish and chips (she was a different person than the waiter who took my order): “Hey, that’s funny, I thought I must be seeing things – there’s a guy inside who is also having a Porter, fish and chips, and using an iPad”. Neat!

I wonder if he is in a Mirror Geometry (Mirror Symmetry)? Turns out you can have two Calabi-Yau spaces with different topologies (shapes) but the same resulting set of physical properties (simplistic: i.e. same universe). I wonder what shape the other guy was? :)

Mirror-symmetry is powerful: if you have a hard time solving a problem (typically in string-theory) with one of the spaces, just use its mirror space! This has been successful in many cases, sometimes allowing problems to be solved that have eluded mathematicians for over a century…

From the lecture description at Smithsonian Resident Associates page:

Do we live in a 10-dimensional universe? String theorists believe we do, even though we can sense only four dimensions.

Geometer Shing-Tung Yau has mathematically proven the existence of the elaborate, twisted six-dimensional shapes at the center of string theory. If that theory is correct, these “Calabi-Yau manifolds” (pictured here) may dictate the forces and particles of nature.

Yau tells the story of how physics met geometry and the new picture of the universe that has emerged as a result. He concludes by describing the ongoing exploration of Calabi-Yau spaces and the quest to uncover the shape of this small, hidden domain that may govern almost everything in our universe.

Lisa Randall at Smithsonian

Lisa Randall at Smithsonian

Lisa Randall at Smithsonian

On Friday (April 24, 2009) I went to see Physicist Lisa Randall receive the Benjamin Franklin Creativity Laureate Award from The Smithsonian Associates and the Creativity Foundation. Professor Randall discussed the role of creativity in her life and work with University of Chicago professor Michael Turner. The talk was in the Baird Auditorium of the National Museum of Natural History – nice venue!

After the talk I was able to get Prof. Randall to sign my copy of her book, “Warped Passages: Unraveling the Mysteries of the Universe’s Hidden Dimensions“. Great book!

From the press release:

Randall is best known for her work involving extra dimensions of space, or “warped” geometries, and her suggestion that could explain the relative weakness of gravity and that we may live in a world with an infinite extra dimension—possibly even in a three-dimensional sinkhole in a higher-dimensional universe. This has resulted in her being one of the most-cited theoretical physicists in the world. Time magazine included her in its 2007 list of the 100 most influential people, and Newsweek cited Randall as “one of the most promising theoretical physicists of her generation.” Her book “Warped Passages” was included in the New York Times’ list of the 100 most notable books of 2005.

Randall is a professor of physics at Harvard University and is tenured at Princeton and MIT. She has served on the editorial boards of several major journals and is a member of the National Academy of Sciences and the American Academy of Arts and Sciences.

Lisa Randall at Smithsonian[/caption]
Lisa Randall at Smithsonian

Lisa Randall at Smithsonian

Lawrence Krauss: Universe

I went to see Lawrence Krauss‘s lecture at the National Academy of Sciences last Thursday night (a Smithsonian Associates lecture). He actually gave two talks, with questions and a break in-between. Professor Krauss is a very engaging speaker, and I quite enjoyed the evening. As usual I videotaped the lecture (this proved useful as I didn’t have to take notes; upon viewing again over the weekend a lot more was able to sink in).

After the talk he signed books (picture at left is Prof. Krauss inscribing my copy of Hiding in the Mirror). He thanked me again for taking and letting Scientific American use pictures from a previous lecture.

I will attempt to summarize the lecture(s):

Part One: “Our Miserable Future” dealt with the sobering thought that the universe will eventually end. Probably. Really.

A major part of cosmology in the 20th century involved trying to determine the geometry of the universe. It is either Closed, Open, or Flat. An Open universe will basically expand forever, while a Closed universe will stop expanding and eventually collapse back in on itself. A Flat universe is right on the border between the two – the expansion will slow over time, but never quite stop.

So, how much “stuff” is there in the universe? Is there enough to make it stop expanding? One way of determining the amount of matter present is via an effect called gravitational lensing. If you look at a certain cluster of galaxies some 2Gly (billion light years) away, you can also detect what turn out to be multiple images of another cluster some 2 Gly behind it. The multiple images form due to gravity from the nearer cluster acting like a lens on the light from the farther one. You can do the math to determine how much matter must be in the nearer cluster to get this effect. It turns out that most of the required matter is not visible – hence, “Dark Matter“.

Based on such indirect evidence, it appears that within 95% certainty there is only about 30% of the amount of matter needed to stop an expansion. So, we are in an Open universe.

But, studies used to measure the geometry of the universe directly (via the Cosmic Microwave Background) show that the universe is actually Flat. How do you reconcile these two very different observations? Well, that’s where “Dark Energy” comes in. We only detect about 30 percent of the mass needed to be a Flat universe (via lensing, etc.) so how to we make up the other 70%? We put energy in empty space. This Dark Energy (in empty space) is gravitationally repulsive.

Scientists looked at the light from a bunch of bright supernovae, and found they were accelerating away from us. Doing the math, they calculated how much energy they have to have in empty space to be “repulsing” the supernovae away from us. It was exactly the needed 70%.

So, the Universe is:

  • 70% Dark Energy
  • 25% Dark Matter
  • 5% The rest (galaxies, stars, planets, humans).

In other words, we are truly insignificant in the universe. :) Also, the nature of Dark Energy will ultimately determine the fate of the universe. That’s the rub – we have no idea what this “Dark Energy” actually is.

The rest of the first part dealt with the concept that a lot of the universe has already disappeared to us, i.e., objects we could have seen 5 billion years ago have already accelerated (and thus redshifted) away from us to such an extent that we can’t detect them. Finally Professor Krauss talked about the ability (or lack thereof) of life (as consciousness) to live forever in an expanding universe:

If Quantum Mechanics ultimately governs a universe starved of energy consciousness will end for any eternally expanding universe. We need Infinite time to determine the Ultimate fate of the universe (and the future of life within it), but we only have a Finite time left.

Part Two of the lecture primarily dealt with the Anthropic Principle, which basically states that the only universe we can see is the one that supports life. In other words the universe is the way it is because we are here. This in a nutshell attempts to answer questions such as:

  • Why are we (life) happening just *now* in the timeline of the universe, when the density of matter just happens to be about 30% of the energy density of empty space?
  • Why is gravity the weakest force in nature?
  • Why is a proton 2000 times heavier than an electron?
  • Why are there 3 generations of elementary particles?


Because if any of these were different, life would not exist (to observe it).

Supposedly String theorists are particularly enamored of this idea, with their “string landscape” that postulates something like 10^500 different universes. One of them is bound to be this one.

Professor Krauss lists some fundamental Anthropic Problems:

  • It is an idea based on ignorance (“We don’t know why”).
  • You never know which variables are anthropically selected.
  • It is never compelling, only suggestive, and
  • It has been wrong before.

String Theory Debate

Brian GreeneLawrence Krauss

Brian Greene (left) and Lawrence Krauss (right), participated in a String Theory Debate last night at the Natural History Museum (Smithsonian Associates Program), with Michael Turner acting as moderator.

More pictures are also available on the photography page.

I recorded the first 75 minutes of the debate (audio only), as well as the last 15 minutes (as video) using my Canon S3. I am very pleased with the audio quality from this camera (samples in stereo at 44khz).

Both Greene and Krauss have written popular books on science, with Greene’s The Elegant Universe selling a million copies. This book was made into a NOVA mini-series, The Elegant Universe, which Greene hosted. Greene’s latest book is The Fabric of the Cosmos.
Krauss has written a number of books, including The Physics of Star Trek and his most recent, Hiding in the Mirror

This was a very lively debate, with Brian Greene taking the “pro” String Theory side (probably since he is a major researcher in the field), and Lawrence Krauss taking the “con” side. Krauss was quick to point out that they are on the same side, unlike the “debates” he has against Intelligent Design proponents (or alien abductees). Both are working scientists; Professor Greene is at Columbia University (physics and math), and Professor Krauss is at Case Western Reserve University (physics and astronomy). Professor Turner is at the University of Chicago.

What is string theory? String theory is an attempt at unification. The theory attempts to unite things that are very big (general relativity; gravity) with the very small (quantum mechanics). Such a unifying theory is very appealing to scientists, but even Einstein was unable to reconcile the two areas.

I’ll summarize (and paraphrase) the points each made below, but it was a long debate, so I’d suggest interested parties listen to the audio recordings.

Greene: String theory is an attempt to unify gravity and general relativity with quantum mechanics. As you go smaller and smaller you see matter made up of atoms (made up of electrons surrounding a nucleus). The nucleus is in turn made up of protons and neutrons, and these in turn are made up of quarks. String theory speculates that if you go a billion billion times smaller, you see that quarks are in turn made up of vibrating “strings”, or “filaments”. Think of a violin string — as it vibrates in different ways, it produces different “notes”. “Elementary” particles, like quarks, can be likened to the “notes” vibrating strings make.

Krauss: The problem is you can’t actually test a single aspect of this; there is no way to “see” something a billion billion times smaller than a quark. [Greene: yes, I said that.]

Krauss: Another issue is that these “strings” are vibrating in a universe that has more dimensions (about 10-11) than the 3 of space and 1 of time we are familiar with. What are these “extra” dimensions? Do they have any basis in reality, or are they just there to make the math work out?

Both agreed that *maybe* the new Large Hadron Collider at CERN will produce something that verifies something, but that’s a big maybe.

Greene did make a comment early on: “If you ask me do I believe in string theory, then the answer is ‘no’ – it can’t be tested yet. But do I believe it is the best shot we have at a unifying theory, then ’emphatically yes’ “. [see the audio recording for the exact quote].

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