gravity
rallain | August 27, 2008Maybe you can tell I am watching the MythBuster's Moon Special. In the show, the MythBusters go in a plane to reproduce the gravitational forces on the moon. I previously went over this, so here is the link:
[Tutorial on how gravity and weightlessness (zero-g) work](http://scienceblogs.com/dotphysics/2008/09/gravity-weightlessness-and-a…)
rallain | August 27, 2008Clearly the MythBusters did this before I did (it's just airing tonight though). I just wanted to say that I posted some videos of the Apollo "jump salute" video analysis and also sped it up to "Earth-like" accelerations. I then made a video of my daughter doing the same thing on Earth and slowed it down. Yes, the MythBusters did it better, but I just wanted to say "me too". My analysis is here:
[Undoing Fake Moon Landing Videos](http://www.dotphys.net/files/moon-time.html)
P.S. I also slowed down a video of Kobe Bryant Jumping so he has an acceleration of that on the moon.
esiegel | May 20, 2008Some of you who've been following astronomy for awhile might remember this report, where a group of astronomers reported finding a giant "void" in the Universe.
What is a void? Well, galaxies are distributed pretty randomly, but because of gravity, they cluster together. A small example is our local group which looks like this,
and a larger example is the Virgo cluster, which is about 1,000 times as massive as our local group, and looks like this:
Well, a void is the opposite of a cluster, where you have a large volume of space that's simply empty of galaxies and matter. This press release…
esiegel | May 13, 2008There is a very techincal paper this morning by Martin Bojowald that asks the question, How Quantum Is The Big Bang? Let me break it down for you.
If you took a look at empty space and zoomed in on it, looking at spaces so small that they made a proton look like a basketball, you'd find that space wasn't so empty after all, but was filled with stuff like this:
What are these? They're little pairs of matter particles and anti-matter particles. They spontaneously get created, live for a brief fraction of a second, and then run into each other and disappear. That's what happens on very small…
esiegel | May 6, 2008(This is adapted from my public lecture, Afraid of the Dark: How We Know What We Can't See.)
Let's go back over 200 years ago, to 1781. William Herschel (left) discovered the planet Uranus, noticing that an object, as bright as a star, was actually moving relative to the other stars. The other five inner planets (besides Earth) were known for over 2000 years before that. But it was thought for a long time that Saturn was the farthest one.
But it clearly isn't; as you can see with modern telescopes, Uranus is a super-interesting planet, rotating on its side, surrounded by rings and moons.…
esiegel | May 2, 2008Can you believe that I had a fight today with someone who's been dead for over 350 years, and I'm losing? -- Ethan, yesterday
Of course you can believe it, when the man I'm fighting with is Johannes Kepler. I don't get a chance to tell you about my research very often, mostly because it's still a work in progress. But my latest paper was just submitted and is now out of the way, and so I'd like to tell you what I'm working on at the moment.
Well, there we are in the galaxy. We look up at the night sky, and we see our planets as well as all the stars that surround us. But you know what we don…
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 28, 2008And if the band you're in starts playing different tunes
I'll see you on the dark side of the Moon.
One of my favorite readers, Zrinka, asks us why we're only able to see one side of the Moon from Earth. Seriously, look at the different phases; we always see the same side of the Moon:
How does this happen? Well, the Moon makes one revolution around the Earth about every 29 days, and that's what causes the Moon phases. But the Moon also rotates once every 29 days also. Because of this, the same side of the Moon always faces the Earth:
We call this "being locked." We're not the only system…
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 19, 2008Sometimes, gravity and motion has the power to mesmerize me. I found this online game called "compulse" which was so much fun, that I spent about 90 minutes this week just playing this game until I had beaten every level on the "pro" setting. Yikes. (My score is 104 under par, 8 under pro.)
And so, in the interest of bringing it to you, I've tried to embed it into my website. Have fun playing if it works in your browser (I told you to use firefox or safari), and if you enjoy playing with the mechanics of motion as much as I do, maybe you, too, have the interest it takes to be a physicist!…
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…
esiegel | April 14, 2008Over the past few months, I have been asked a number of questions about String Theory and the Universe, including from readers Benhead and Mastery Mistery. But now Jamie, whom I'm going to marry later this year, has been asking me about it, and so it's time to write something about the scientific topic of String Theory. (Send in your questions now, because I'll answer them all this week if there's enough interest.) Let's start with this pair of questions:
String theory has been around for over 20 years, and so far, there is not one shred of experimental or observational evidence in support of…
esiegel | April 3, 2008Two summers ago, I was in Les Houches, France, for a summer school that turned out to be one of the best experiences of my life. Seriously, we'd wake up every day and this was the view from the school:
Well, the University/Institution that ran the school sends periodic updates to me. And they linked me to this release. Here's the interesting and (if it's true) sensational claim that the release makes:
Recently, a team of theorists ... performed a new analysis of all available CMB and LSS data including the WMAP and Sloan data and favor an inflation model where exist primordial gravitational…
esiegel | March 26, 2008So last week I was up at Pacific University in Portland, OR for a job interview. As part of a faculty interview, you have to lecture on a topic for undergraduates, but they give you the topic just a couple of days before. My topic was Gauss' Law, which talks about the relationship between an Electric Field and an Electric Charge. Well, the same law holds for Newton's theory of Gravitation with a gravitational field instead of an electric field and a gravitational charge (i.e., mass) instead of an electric charge.
So I'm at work today thinking about this, doing the thing I do messing around…
esiegel | February 29, 2008The Milky Way galaxy is a relatively big spiral galaxy. So is Andromeda. There are about 20 dwarf galaxies that are gravitationally bound to us; combined with us, all of this makes up the local group. But Andromeda is moving towards us, and eventually, it's going to merge with us. I'll once again show you a video of what this merger might look like:
But what would we see, here in the Milky Way, as Andromeda got closer and closer to us? Right now, Andromeda looks like this:
But Andromeda is also very far away: about 2.3 million light years (770 kpc). The center of it is tiny on the sky, but…
esiegel | February 27, 2008The Moon goes around the Earth, the Earth goes around the Sun, and the Sun goes around the center of the Milky Way. We know the Moon takes about 4 weeks to make its trip around the Earth, and that causes the Moon phases:
We also know that the Earth takes one year to go around the Sun, and that causes the seasons:
We also know that the Earth has been around for about 4.5 billion years, which means it has gone around the Sun about 4.5 billion times. Well, now I ask the question(s):
How long does it take the Sun to go around the Milky Way? How many times has it done that so far, and how many…
esiegel | February 21, 2008Alright; this is a question I've been putting off for various poor reasons, but Starts With A Bang! reader Andy asks:
If Im looking at something, the light from which has taken 15 billion years to get to me, and there was only an opaque ball of radiation and stuff 15 billion years ago, why do I see formed galaxies? Shouldnt the age of the universe be: TIME LIGHT FROM OBJECT TAKES TO REACH ME + TIME TAKEN TO FORM OBJECT IM LOOKING AT?
In other words, how can I see things like galaxies that are 15 billion light years away, if the Universe isn't even 15 billion years old?! This is a damned good…
esiegel | February 19, 2008Last week, Pamela Gay over at Star Stryder pointed me to a press release which claimed that, among other things, perhaps dark matter wasn't necessary. So I wrote a guest post on her blog explaining why it was. Apparently, some people still aren't convinced. So I will lay out for you all the reasons I can think of why we need it, and explain what happens if you try to do without it.
1. Cluster Velocity Dispersions. When we take a look at galaxies, we often find hundreds or even thousands of them clustered together, like in the Coma Cluster. We can measure how quickly those galaxies are moving…
esiegel | February 13, 2008I've been talking about dark matter a lot, and yet there's still so much to explain about it. For example, dark matter and normal matter (protons, neutrons, and electrons) have a few things in common:
They both have mass.
They both feel the effects of gravity.
They both cause their own gravity.
But that's where the similarities end. I can make a long list of the ways that dark matter and gravity are different from one another, but I prefer to give you an example. Imagine the following scenario: you stand up from your seat, walk towards the wall, and smack right into it. You might wind up…
esiegel | February 13, 2008Last week, Jamie (my significant other) came home from work and told me about a conversation she had with her coworker, Chris. This week she asked another one, Miguel, whether he had any questions about Astronomy, Physics, space, etc. This week's question comes from Miguel:
What is a galaxy, anyway? Why does it look like a big bright fuzzy star? And why are there different types of galaxies; shouldn't they all be the same?
This might come as a surprise, but 100 years ago, it was pretty much accepted that we were the only galaxy in the Universe. In fact, there was a great debate in 1920 on…