Relativity
esiegel | January 5, 2011"The size of the universe is no more depressing than the size of a cow." -David Deutsch
But it is bizarre, I'll give you that. The most common scientific question I get asked is how, if the Universe is 13.7 billion years old, and the speed limit of the Universe is the speed of light, why do I say the observable Universe is 93 billion light years across?
In other words, why is this picture of the Universe wrong?
I've tried to answer this before, and so have others, but perhaps it's time for another -- more conceptual -- attempt. This is one of the most mind-boggling things about relativity.…
drorzel | October 11, 2010SteelyKid, like most toddlers, knows a few songs, and likes to sing them over and over. Her repertoire is limited to "ABCDEFG" (the alphabet song, but that's how she requests it), "Twinkle, Twinkle," "Some man" ("This Old Man," which I only figured out this weekend), and "Round and Round" ("The Wheels on the Bus"). I get a little bored with the repetition, and so tend to make up my own verses, which get sideways looks from her, followed by telling Kate "Daddy's silly!"
I've been posting a lot of these on Twitter over the past several days (@orzelc), but for posterity, a few physics-related…
esiegel | October 8, 2010"You can't have a light without a dark to stick it in." -Arlo Guthrie
You know the story. Every galaxy we look out at, with hardly any exceptions, appears to be moving away from us. Not only that, but the farther away a galaxy appears to be, the faster it appears to move away from us!
What do we observe that leads us to believe this? Well, thanks to Edwin Hubble, who looked at the spectra of distant galaxies, we discovered that, compared to Earth, where we make atoms emit and absorb light at very specific wavelengths (or frequencies):
for distant galaxies, these emission/absorption lines…
drorzel | September 8, 2010The theory of relativity takes its name from a very simple and appealing idea: that the laws of physics should look the same to moving observers as to stationary ones. "Laws of physics" here includes Maxwell's equations for electricity and magnetism, which necessarily means that moving observers must see the same speed of light as stationary observers (Einstein included the constancy of the speed of light as a second postulate in his original relativity paper, but it's redundant-- the constancy of the speed of light is a direct consequence of the principle of relativity). This leads directly…
esiegel | September 3, 2010"We have been forced to admit for the first time in history not only the possibility but the fact of the growth and decay of the elements of matter. With radium and with uranium we do not see anything but the decay. And yet, somewhere, somehow, it is almost certain that these elements must be continuously forming. They are probably being put together now in the laboratory of the stars. ... Can we ever learn to control the process. Why not? Only research can tell." -Robert Millikan
Ah, energy, if only you were free, limitless, and easily accessible. If you were, we could do anything we wanted…
drorzel | September 2, 2010"Hey, dude, whatcha doin'?"
"Signing these contracts. I'm not sure why they need four copies, but they do."
"Contracts for what?"
"The new book. Remmeber, the one we've been talking about these last few weeks? Sequel-of-sorts to How to Teach Physics to Your Dog? About relativity?"
"Oh, yeah, that's right! We're doing another book! Where do I sign?"
"What do you mean, 'Where do I sign?' You're a dog."
"I could, you know, put a paw print on the line, or something."
"I suppose you could, but it wouldn't be legally binding. Dogs aren't allowed to sign contracts."
"You know that's horribly…
esiegel | August 30, 2010"The whole fabric of the space-time continuum is not merely curved, it is in fact totally bent." -Douglas Adams
As many of you know, if you take a whole bunch of mass, and you've got nothing going on except gravity, it's going to gravitationally collapse. And if atoms, nuclei, pressure, and nuclear reactions don't (or can't) prevent that gravitational collapse from running away, you're going to wind up with a black hole.
But last week, I told you that if you took all the matter in the Universe and shaped it into a cylinder, you'd actually wind up with a huge cylinder of solid matter, as big…
esiegel | August 25, 2010"The only problem with the speed of light, is it gets here too early in the morning." -Danny Nevrath
One of the most common questions I get asked is whether gravity is instantaneous, or whether there's a speed limit to how fast the force of gravity can travel.
It's a good question! After all, we know how fast light travels, and if the Sun were to suddenly wink out of existence, we'd still receive light from it for just over 8 minutes after it disappeared! But what about gravity, and the Earth's orbit? Would the Earth simply fly off in a straight line, like a twirled poi ball the instant a…
esiegel | July 14, 2010"I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use." -Galileo Galilei
Geez, Ethan, why don't you take on a bigger question?
This question of "fundamental things" has a special meaning to scientists and natural philosophers, going all the way back to Thales of Miletus, 2600 years ago, who began asking about the arche (αρχή), which is the "element" or "prime cause" of existing things.
Of course, the scientific enterprise was just beginning, so you can't fault Thales too much for coming up with "water". But…
drorzel | June 5, 2010Since I was going to be down here anyway to sign books at the World Science Festival Street Fair, Kate and I decided to catch one of the Saturday events at the Festival. It was hard to choose, but we opted for the program on Hidden Dimensions: Exploring Hyperspace (Live coverage was here, but the video is off), because it was a physics-based topic, and because I wrote a guest-blog post on the topic for them.
(No, we didn't go to the controversial "Science and Faith" panel, opting instead to have a very nice Caribbean dinner at Negril Village, just around the corner. I'll take excellent…
hrynyshyn | June 3, 2010Much has been written of late about the nature of denialism. New Scientist a couple of issues back produced a special report on the subject, for example, and the New Humanist explores the idea of "unreasonable doubt."
There's plenty more out there. The most provocative I've come across (thanks to Joss Garman via DeSmog Blog's Brendan DeMelle) is a 2009 paper in the journal Studies in History and Philosophy of Modern Physics by Jeroen van Dongen of the Institute for History and Foundations of Science at Utrecht University in The Netherlands. His thesis is ideologically based denialism of…
drorzel | April 8, 2010Via Twitter, Michael Barton is looking for some good books about physics. I was Twitter-less for a few days around the period of his request, and this is a more-than-140-characters topic if ever there was one, so I'm turning it into a blog post.
The reason for the request is that he's going to be working as an intern at the Einstein exhibit when it visits Portland, which makes this a little tricky, as relativity is not an area I've read a lot of popular books in (yet-- that's changing). That will make this a little more sparse than it might be in some other fields.
There's also an essential…
esiegel | March 23, 2010Note: I'm on vacation this week, so here's one from the vault. This article first appeared on my old website, back in February of 2009.
Some days the questions I get are easy, and some days I get questions from our longtime reader, Ben. This past week, there have been reports all over the news that our world may be a giant hologram. Let's take a look at what's going on.
In Hanover, Germany, there's an experiment called GEO600. These are two perpendicular lasers, and they shoot out for thousands of feet, get reflected, and come back to their original location to make an interference pattern…
drorzel | February 3, 2010Yesterday's post on a variation of the "Twin Paradox" with both twins accelerating was very successful-- 337 people voted in the first poll question, as of a little before 9am, and the comments to the original post are full of lively discussion. That's awesome.
I wish I could take credit for it, but the problem posed is not original to me. It comes from a 1989 paper in the American Journal of Physics, which also includes the following illustration setting up the situation:
The article contains a full explanation, and also the following figure illustrating the result:
The correct answer is…
drorzel | February 2, 2010Just about everybody has heard of the Twin Paradox in relativity: one twin becomes as astronaut and sets off for Alpha Centauri, the other remains on Earth at mission control. Thanks to time dilation, the two age at different rates, and the one who made the trip out and back ends up younger than the one who stayed behind.
Of course, the paradox is not that the two twins have different ages-- rather, it's that from a simple approach to special relativity, you would think that each twin should see the other's clock running slow, since it seems like getting into a rocket and flying off into…
esiegel | January 8, 2010The more I examine the universe and the details of its architecture, the more evidence I find that the universe in some sense must have known we were coming.
-Freeman Dyson
When we look out at our Universe today, we see all sorts of beautiful things throughout space, from galaxies and clusters, distributed roughly evenly throughout space:
to the cosmic microwave background (also known as the last scattering surface), radiating at the same temperature in all directions.
We also see, when we try to measure the shape of the Universe, that there are three major possibilities: it could be flat…
esiegel | November 20, 2009Why it is that of all the billions and billions of strange objects in the Cosmos -- novas, quasars, pulsars, black holes -- you are beyond doubt the strangest? -Walker Percy
When you watch someone fall into a black hole, what you actually see is pretty surprising. You see, a black hole's gravity distorts the space around it, and it does so without providing any light of its own, giving you a unique perspective on the Universe.
Well, if you watch someone else fall in, you'd see them approach the black hole normally, and then the bizarreness starts. As they go deeper and deeper into the…
esiegel | October 19, 2009If people around you aren't going anywhere, if their dreams are no bigger than hanging out on the corner, or if they're dragging you down, get rid of them. Negative people can sap your energy so fast, and they can take your dreams from you, too.
--Earvin "Magic" Johnson
As far as science goes, we all have our own dreams. For me, it's to understand the largest scales in the Universe: the most massive structures, the highest energies, and the earliest times of existence.
Particle physicists are also after understanding the Universe at its highest energies, and that's one of the primary goals…
esiegel | August 25, 2009There's a new book out there, Why Does E=MC2 (and Why Should We Care?), by Brian Cox and Jeff Forshaw. One of Seed's editors, Elizabeth Cline, took a read through it and wrote about her experiences and what she learned. Is relativity, particle physics, and all the related science really incomprehensible to all except the scientists working on it? Cox and Forshaw don't think so, and neither do I. So I wrote an article for SEED Magazine here. Here's an excerpt:
Inside of every atom -- every proton, every neutron, every electron, even every neutrino in the Universe -- lies the secret of…
esiegel | August 13, 2009Okay. Yesterday, I explained to you that the only thing that determines how the Universe expands is the amount of energy density in it. But many of you wanted more details. So, by popular demand -- including one insistence that there is no equation that tells us how the Universe expands -- here is the simplest explanation with math that I can come up with for the expanding Universe. If you hate or don't care about math, do not read this. This article is not for you. But if you're curious, read on.
Image credit: Wayne Hu.
First, let me tell you the underlying assumption behind all of it. You…