Waves
drorzel | May 11, 2011While Kenneth Ford's 101 Quantum Questions was generally good, there was one really regrettable bit, in Question 23: What is a "state of motion?" When giving examples of states, Ford defines the ground state as the lowest-energy state of a nucleus, then notes that its energy is not zero. He then writes:
An object brought to an absolute zero of temperature would have zero-point energy and nothing else. Because of zero-point energy, there is indeed such a thing as perpetual motion.
This is really the only objectionable content in the book, but he certainly made up in quality what it lacks in…
drorzel | August 19, 2010At the tail end of Tuesday's post about wind and temperature, I asked a "vaguely related fun bonus question:"
If the air molecules that surround us are moving at 500 m/s anyway, why isn't the speed of sound more like 500 m/s than 300 m/s?
This is another one that people are sometimes surprised by. The answer is simply that in a sound wave, the air molecules don't really go anywhere. When something creates a sound-- say a foolish dog barking at a perfectly harmless jogger going by outside, to choose an example completely at random-- there isn't any actual thing that travels from the noisy dog…
cwilcox | June 20, 2010Wave breaking in Alabama (Photographer Dave Martin/AP) versus wave in Hawaii (Photographer Clark Little)
Which do you prefer?
rallain | September 17, 2009Yes, this can be very complicated. But what should a middle-school student understand about light? You see stuff in textbooks that is either wrong or just a bunch of disconnected factoids (I like the word factoid). So, what do I think is important about light (not at the Maxwell's equations level)
What is a wave
If you want to talk about light, you need to talk about waves. So what is a wave? I like to start with an example. Suppose you are in a sports stadium - maybe a football game. Some inspired fan decides to start a wave. If you look at the individual people, the wave might be…
rallain | November 11, 2008One of the fundamental aspects of physics is the study of light and how that interacts with matter. I have been putting off this post - mainly because I am not a quantum mechanic (I am a classical mechanic). There are lots of things that could be done in this post, but I am going to try and keep it limited (and maybe come back to the interesting points later). Also, most of my posts are aimed at the intro-college level or advanced high school level. This will be a little higher. If you are in high school, there is still a lot of stuff for you here.
Let me summarize where I am going to…
esiegel | April 29, 2008No, not because it was too young to drink! Scientists at the Max Planck Institute for Extraterrestrial Physics were looking at some X-ray objects, and discovered something really weird: a very bright X-ray source moving out of a galaxy at nearly 3,000 kilometers/second! This thing is a goner. If our Sun were moving at even one quarter of that speed, it would get thrown out of our galaxy.
Now, here's the kicker: this isn't just any old object getting tossed out of a galaxy, it is a huge black hole! How huge? About 300,000,000 times the mass of our Sun. You read that number right: 300,000,000…
esiegel | April 24, 2008So as a full member of both the American Astronomical Society and the American Physical Society, I get sent issues of the magazine Physics Today. Well, I was going through the April issue, when I saw this article:
Cosmic Sound Waves Rule
by Daniel J. Eisenstein and Charles L. Bennett
That first name sounds familiar. Why? Because he's my boss! The article requires a subscription, but seeing as how this is what my research is, why don't I tell you what the big idea is.
The Universe is full of dark matter, normal matter, and radiation. When it's young, the radiation is more important than matter…
esiegel | April 17, 2008Nothing gets past you, does it? A scientific paper came out earlier this week, and I took a look at it, sighed, and Jamie asked me, "What?" And I said to her, "When I see bad science, it just makes me a little bit frustrated and sad." Of course, I had no intention to write about it.
But then Starts With A Bang reader Matt emailed me, and writes the following about this press release that he had seen:
You have two explanations for these gravitational waves now and that much I understand. But they make it sound as if symmetry breaking and inflation are competing theories. They aren't, right? Do…