March 25th, 2008
I love working at a university and being surrounded by cosmologists. In my last post, I alluded to the idea that astronomers may one day regret calling the impulsive force pushing spacetime apart dark energy.
I was chatting with a colleague last week where we talked about this nomenclature. It may turn out that dark energy is neither, but for very innocent reasons, the term dark energy has stuck.
The term probably came about from the discovery of dark matter. The existence of dark matter was inferred from a variety of observations of both the microwave background radiation and the Bullet Cluster of galaxies. The behavior of the matter we could see was influenced by something we couldn’t see (from its gravitational field).
The gravity from the dark matter was affecting the matter we could see.
Likewise, with respect to dark energy, the discovery that the acceleration of the universe was also being caused by something we couldn’t see nor detect, it seemed natural to call whatever that was dark energy.
Dark matter, dark energy, tomato, tomato…
Sean Carroll prefers the term smooth tension.
Dark energy can more accurately be thought of as a negative pressure.
Imagine a gas inside a bottle. Our everyday experience shows that if you left the same amount of gas in the bottle but made the bottle bigger, the pressure would go down. If you made the bottle smaller (leaving everything else the same), the pressure would go up; the molecules in the gas exert a positive pressure.
If that gas was dark energy, the pressure would increase as the bottle got bigger, and decrease as it got smaller.
Another way, usually described by Sean Carroll (and I’m paraphrasing poorly here), imagine a cylinder where the pressure increases when you pull the piston out.
Pulling the piston actually increases the energy in the system, while pushing decreases it.
Above photo credit: goatopolis
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March 25th, 2008
Sometimes when I write a blog post, I think of this line spoken by Jeff Goldblum’s character in “The Big Chill”, referring to how he writes for People Magazine:
“Where I work, we only have one rule: we can’t write anything longer than the average person can read during the average crap.”
Many people who read blogs, and that includes myself, just don’t have time to read several hundred-word posts; we skim and we glance to get to the interesting stuff. In fact, it’s about the only way I read content on the web, for better or worse.
While I’ve already written a few, I wanted to write a series of long-ish posts about dark energy. Being realistic about my time (and yours), I’ve decided that I’ll be a little less ambitous and break them down to some smaller bite-sized chunks (I’ll probably write the same ideas a bunch of different ways before it’s all over in order to help you make sense of this stuff, it’s pretty hard to visualize).
Whether you read them during an average crap is up to you.
Let me start by characterizing what we think we already know about dark energy (ooh look he’s using semi-colons):
- It makes up 70% of the universe. You’ve read this a million times by now. The inventory of the universe goes like this: 5% normal matter (that’s you, me, people magazine, atoms, molecules, etc); 25% dark matter (that’s the stuff that has mass but doesn’t interact with the universe in any meaningful way, except with gravity); 70% something else (astronomers started calling it dark energy, they may regret that one day).
- Causes the universe to be flat. If the universe only had normal matter and dark matter, it wouldn’t be flat because there isn’t enough of it. Since the universe IS flat, there must be something there to cause it to be that way. They’re naming that thing dark energy.
- It is an impulsive force that pushes against spacetime. As the universe expands, the fabric of space is filled with this stuff, and when it appears, it provides an impulse - further pushing spacetime. It’s not negative gravity, but can be visualized that way if it makes you more comfortable, it’s actually more of a negative pressure.
- Is causing the acceleration of the universe. Add up all these little impulses throughout the fabric of spacetime and you get a substantial push, and the push becomes stronger as there is more of it. Spacetime expands, dark energy appears providing an impulse pushing things apart causing more expansion, etc… What you’re left with is a universe that may just fly apart and slowly evaporate.
- It is smooth and persistent throughout the universe. Whatever dark energy is, it is everywhere (more or less homogeneous) and once it’s there, it stays there in roughly the same density as the universe expands.
- It’s probably not a particle. Umm, I should probably say more here, huh? If it is a particle, it’s probably more like the as-yet undiscovered graviton. Let’s leave it there for now…
Who else but a blogger would think he can summarize something as complex as the nature of the universe in a six-point ordered list?
And yet, I do it anyway. At least I wasn’t on the crapper when I wrote it. You may feel otherwise.
Above photo credit: Lawrence Whittemore
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By Tony -- 2 comments
March 23rd, 2008
The caption on wikipedia for this woodcut reads as thus, “An engraving by Albrecht Dürer, from the title page of the Masha’allah ibn Atharī’s astronomy treatise De scientia motus orbis (Latin version with engraving, 1504). As in many medieval illustrations, the compass here is an icon of religion as well as science, in reference to God as the architect of creation.”
I look at this woodcut and I see less an icon of religion and science (note: religion and science are two words that should NOT go together), and more so an icon of the rare, I assume non-existent, linkage between cosmology and cosmetology.
We see here, depicted in this woodcut, the unlikely, unprecedented image of an astronomer sitting in the cosmic salon chair of the universe, about to get his hair “did”.
Ahhhh, cosmology and cosmetology meet at last.
Salon Picture of curly-haired woman photocredit: un_cola
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March 22nd, 2008
I read a short piece of fiction recently that I really thought was good. As with most pieces of fiction, there is a certain degree of truth within it, and, in this case, it is of a factual historical reference to George Ellory Hale. For though the speaker of this short story, reminiscing about his high school alma mater, is fictional, the character of Hale was really like the story describes. Hale was a solar astronomer (1868-1938) born in Chicago, Illinois. Even as an undergrad at MIT, he really made some waves by inventing the spectroheliograph that he used to discover solar vertices and magnetic fields of sunspots.
I read more about him on this website: http://www.mwoa.org/hale.html, and apparently, George Ellery Hale was the founding father of the Mt. Wilson Observatory. What is funny to me is he called his observatory the “monastary”. I always felt like observing in the mountains alone was akin to being like a monk in a monastary. So, in this regard, I can totally relate to Hale.
A motivated man, Hale would work himself to death, and like so many geniuses, would straddle the line between supreme intellect and insanity. He would at times hallucinate while staying up for long hours working. Despite this, he was a major catalyzing force in the founding of the Palomar Observatory and the building of the 200 inch “Hale” telescope.
Anyway, I digress, so here is a link to the great short story I was speaking of originally:
THE TELESCOPE BUILDER by Steve Silkin (published by Eclectica online mag)
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March 21st, 2008
According to the New World Enclyclopedia:
Historically, the term mathematicus was used to denote a person proficient in astrology, astronomy, and mathematics.[1]
or the plural, if there are more than one: “mathematici”. It is strange to think of a world in which astrology was considered mathematical. But, pretty much every early civilization incorporated some kind of astrology into their “sciences” and religions. Hocus pocus=mathematicus.
Astrology is an example of how a feeling of wonder and awe can produce an artificial feeling of religious experience and an encounter with something supernatural. It is that human need to rely on a constant for a feeling of stability.
I think of astrology sort of like this: Some people need a sort of “baby mobile”, with balls of planets and stars hanging over them, forming pretty, connect-the-dot animals and pictures in the sky to point to, reassuring them that the future has a naturally predestined plan, and that they are not lost.
And, what is also interesting is this little tidbit story about an astrologer–according to wikipedia:
A favourite topic of the astrologers of all countries has been the immediate end of the world.
This did not prevent [the astrologer] Stöffler from predicting a universal deluge for the year 1524 - a year, as it turned out, distinguished for drought. His aspect of the heavens told him that in that year three planets would meet in the aqueous sign of Pisces. The prediction was believed far and wide, and President Aurial, at Toulouse, built himself a Noah’s ark - a curious realization, in fact, of Chaucer’s merry invention in the Miller’s Tale.
I find this story really funny. I can just imagine such a thing happening…. An astrologer tells people that there is going to be a flood of biblical proportions. Then the naive president of Germany goes so far as to build a really big ark, sits in it, not unlike a child in a tub, awaiting its bath, waits patiently for God to shoot his wad, to unleash his great waters of wrath, waits and waits, gullibly, for a grand climax, and then…. nothing. Ha, ha sucker, that’s what chicken little gets for believing the bunk of an astrologer.
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March 21st, 2008
These last couple of weeks have seen me writing code to ingest the images the DES camera will take when it goes online into our database.
The numbers are staggering. Each night, we’ll produce 300GB of data for a total of about 165 terabytes by the end of the survey, and that’s just the raw data that come off the ccd’s.
Once these raw data are processed into science images, we’ll have around 1.7 petabytes of processed data sets. If we reproces at the end of each season and keep everything, the total DES data set will reach 7 petabytes.
How is it that we have so much data? In order to characterize the nature of dark energy, we need lots of pictures that cover a lot of the sky in a number of wavelengths.
The DES camera has 62 2k by 4k ccd’s arranged in a hexagonal array that collectively make a 520 megapixel camera. The camera will take 100 - 400 sec exposures each night in four wavelengths.
The camera will read out each exposure from the 62 ccd’s and send them to us for processing and storage. How many we get after a night’s observing will depend on the weather and other factors, but we anticipate 300GB each night we do this.
And the DES project has reserved roughly 30% of the observing nights over five years on the 4 meter Blanco telescope at the Cerro Tololo Inter-American Observatory in South America.
This is the future of astronomy, lots and lots of image data that fill up petabyte scale supercomputing facilities. Organizing these data so that science can be done is no small task, and I’m thrilled to be on the forefront of some of the technologies that will serve this to scientists.
One thing hit me hard the other day: we were discussing image compression and which method we would use. During the discussion someone asked, “Why do we need to do ANY compression?”
It’s actually not so crazy an idea. Disk space is cheaper than CPU time, at least on the scale we’re operating on, why waste cpu cycles compressing and decompressing when we can just serve uncompressed images?
Another big sticking point is that many people who view astronomy images in their scientific format, known as fits, can’t seem to agree on a compression scheme across the various viewers out there. Some viewers can use gzip compression for example, but not RICE. Others can’t support compression at all.
Personally, I think we’ll be compressing images for a long time, but we’ll be smarter about it. I have been a big proponent of wavelet compression in astronomy images for a long time. If I could somehow get others to think about it, who knows?
Anyway, just a little glimpse into my world these days.
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March 21st, 2008
The Russian astronomer Wilhelm Struve, full name: Friedrich Georg Wilhelm von Struve, (1793-1864) completed 272 astronomical works and fathered a grand total of 18 children.
That’s a lot of baby von Struves! Some of his most recognized observations were of double stars. He carried on the work begun by William Herschel, who discovered that many double stars were two stars revolving around each other.
Side note:
While both William and John Herschel (his son) observed many double stars, they didn’t record anywhere near as many as Struve, who measured the widths of a whopping 2714 double stars.
In contrast, his great-grandson, Otto Struve (1897-1963), the Russian-American astronomer, recognized for his contributions to stellar spectroscopy, produced 907 works (over 3 times as many as his great grandfather) and had zero children.
Apparently, having 18 children significantly reduces one’s ability to produce astronomy publications.
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March 15th, 2008
Apparently there was a research lab at the University of Hertfordhire that was appropriately named the “LaughLab”. Yes, LaughLab. Sounds like a lab run by clowns….which happens more commonly in science labs than one would come to expect, but I digress…
LaughLab’s research interest had to do with what made a joke funny and especially what made a joke universally funny. To figure this out, the lab made a website in which people could submit jokes and rate other people’s jokes. The researchers then figured out which jokes were rated the funniest and why. Like, for instance, some jokes were funnier to men, some funnier to women, and some jokes’ punch lines were not understandable to other cultures. The two funniest jokes got the prizes of World’s Funniest Joke and the World’s Second Funniest Joke.
What’s great about all this is that the World’s SECOND Funniest Joke was astronomy-related. And, get this, not just astronomy-related but also Sherlock Holmes and Watson related….
The joke is actually pretty funny, though I am not sure it really qualifies for second funniest joke in the world. Ah, well, you be the judge.
See: www.wikipedia.org/wiki/World’s_funniest_joke
It goes like this:
Sherlock Holmes and Dr. Watson go on a camping trip. After a good dinner and a bottle of wine, they retire for the night, and go to sleep. Some hours later, Holmes wakes up and nudges his faithful friend.
“Watson, look up at the sky and tell me what you see.”
“I see millions and millions of stars, Holmes,” replies Watson.
“And what do you deduce from that?”
Watson ponders for a minute.
“Well, astronomically, it tells me that there are millions of galaxies and potentially billions of planets. Astrologically, I observe that Saturn is in Leo. Horologically, I deduce that the time is approximately a quarter past three. Meteorologically, I suspect that we will have a beautiful day tomorrow. Theologically, I can see that God is all powerful, and that we are a small and insignificant part of the universe.
What does it tell you, Holmes?”
Holmes is silent for a moment. “Watson, you idiot!” he says. “Someone has stolen our tent!”
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March 14th, 2008
Photo Credit: Abulic Monkey
I was looking at Flickr images on the internets and I came upon this photograph that somebody took of a sign at a store that sells telescopes.
Oh, how many times have I felt the sting of pain brought on by my telescope kicking me in the dark of night. Yea, for I have walked through the valley of mean telescopes and have the bruised shins to prove it.
It’s important to remember when shopping for your telescope to also purchase shin guards and maybe leather chaps. Some telescopes respond well to those electronic shock-collars as well.
Be careful out there, people.
If do right, no can defense!
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March 13th, 2008
I was just reading more about Flammarion (1842-1945), the French astronomer wood-cut picture guy. He wrote lots of books and was a Spiritualist (meaning he believed in other worlds of spirits and ghosts). He lived during the peak popularity of the Spiritualist movement.
I’m not going to name any names but some astronomers are pretty far out there. Like, REALLY far out there (remember all that Martian canal business? How about the lush gardens we’d find on Venus?).
Back in the day, some of the stranger ones managed to accomplish some really good science, and then counteract it with total rubbish. I guess back then you could better get away with things like that.
Flammarion did write some serious science books and good research. In fact, there are two craters, one on Mars and one on the Moon, and even an asteroid named after him. He published many popular books on astronomical including L’astronomie Populaire in 1879, which sold over 100,000 copies, but he also published many books on reincarnation and spiritualist topics. All in all, though, he was a very prolific writer for the times, who had some very interesting scientific ideas on evolution and life on other planets.
According to Wikipedia, he first suggested the names Triton and Amalthea for the moons of Neptune and Jupiter, respectively. . In 1877, he founded the Astronomical Society of France, and in 1882, he a private estate observatory was left to him in a will by a dead rich guy named M. Meret who admired his work.
Finally, it turns out that people really liked to leave him stuff when they died and he was popular with the ladies. In fact, he had many female admirers. One such lady, though she had never met him personally, had Flammarion’s portrait tattooed upon her body. When she died of tuberculosis, she specially requested a doctor remove her skin to make a special human-skin, tattoo leather book cover edition for his next book. It was a beautiful act of morbid love. Flammarion honored her wishes and made sure the first copy of his book Terres du Ciel was bound thus. And the inscription on the front cover said: ‘Pious fulfillment of an anonymous wish/ Binding in human skin (woman) 1882′.
I didn’t know human skin would make for a good leather binding.
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