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Archive for August 20th, 2015

Complex dark matter may include dark-matter atoms and photons

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Dark matter may be much more complex than we have assumed. Liz Kruesi of Quanta interviews the physicist James Bullock:

Dark matter — the unseen 80 percent of the universe’s mass — doesn’t emit, absorb or reflect light. Astronomers know it exists only because it interacts with our slice of the ordinary universe through gravity. Hence the hunt for this missing mass has focused on so-called WIMPs — Weakly Interacting Massive Particles — which interact with each other as infrequently as they interact with normal matter.

Physicists have reasons to look for alternatives to WIMPs. For two decades, astronomers have found less dark matter at the centers of galaxies than what WIMP models suggest they should. The discrepancy is even worse at the cores of the universe’s tiny dwarf galaxies, which have few ordinary stars but lots of dark matter.

About four years ago, James Bullock, a professor of physics and astronomy at the University of California, Irvine, began to wonder whether the standard view of dark matter was failing important empirical tests. “This was the point where I really started thinking hard about alternatives,” he said.

Bullock thinks that dark matter might instead be complex, something that interacts with itself strongly in the way that ordinary matter interacts with itself to form intricate structures like atoms and atomic elements. Such a self-interacting dark matter, Bullock suspects, could exist in a “dark sector,” somewhat parallel to our own light sector, but detectable only through the way it affects gravity.

He and his colleagues have created numerical simulations that predict what the universe would look like if dark matter feels strong interactions. They expected to see the model fail. Instead, they found that it was consistent with what astronomers observe.

Quanta Magazine spoke with Bullock about complex dark matter, how this mysterious mass might behave, and the best places in the universe to find it. An edited and condensed version of the interview follows.

QUANTA MAGAZINE: What do we know about dark matter?

JAMES BULLOCK: We are confident that it’s there, that it has mass, and that it tugs on itself and on other things via gravity. That’s about it. While dark matter has a gravitational tug, it doesn’t interact with normal matter — the stuff that makes up you and me — in a very intense way. It doesn’t shine. It’s invisible. It’s transparent. It doesn’t glow when it gets hot. Unfortunately, those are the ways astronomers usually study the universe; we usually follow the light.

So we don’t know what it’s made of?

We’ve come to understand that we can describe the world that we experience by theStandard Model of particle physics. We think of the particles that make up you and me as being broken down into constituent things, like quarks, and those quarks combine into neutrons and protons. There is a complicated dance that allows these particles to interact in certain ways. It gives rise to the periodic table of elements and all of the vast complexity we see around us. Just 20 percent of the mass of the universe is all of this complexity.

On the other hand, dark matter makes up something like 80 percent of the mass. First-guess models for what it is suggests that it is one particle that doesn’t really interact with much of anything — WIMPs. These are collisionless, meaning when two dark matter particles come at each other they basically go through each other.

Another possibility is this 80 percent of the universe is also complex. Maybe there’s something interesting going on in what’s called the dark sector. We know that whatever ties us to the dark matter is pretty weak or else we would have already seen it. This observation has led to the belief that all the interactions that could be going on with dark matter are weak. But there’s another possibility: When dark matter particles see themselves, there are complex and potentially very strong interactions. There even could be dark atoms and dark photons.

Those two worlds — this dark sector and our own sector — only communicate by gravity and perhaps other weak processes, which haven’t yet been seen.

How can you probe this dark sector if you can’t interact with it? . . .

Continue reading.

Written by Leisureguy

20 August 2015 at 5:44 pm

Posted in Science

How DuPont slipped past the EPA

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Sharon Lerner continues the series on DuPont and C8, a toxic substance that is used to make Teflon and is now found in the bloodstream of 99.7 percent of Americans and in the environment. The current installment in the series explores the reasons the EPA failed to take action against the pollutant.

Written by Leisureguy

20 August 2015 at 3:54 pm

The Poem Everyone Loves and Everyone Gets Wrong

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The Road Not Taken
by Robert Frost

Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth;

Then took the other, as just as fair,
And having perhaps the better claim,
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same,

And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.

I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.

David Orr has an interesting comment on this poem, and I have to admit that I fall into the group that didn’t get it. He writes:

My poems—I should suppose everybody’s poems—are all set to trip the reader head foremost into the boundless. Ever since infancy I have had the habit of leaving my blocks carts chairs and such like ordinaries where people would be pretty sure to fall forward over them in the dark. Forward, you understand, and in the dark. 
     —Frost to Leonidas W. Payne Jr.,November 1, 1927

The Road Not Taken” has confused audiences literally from the beginning. In the spring of 1915, Robert Frost sent an envelope to English critic Edward Thomas that contained only one item: a draft of “The Road Not Taken,” under the title “Two Roads.” According to Frost biographer Lawrance Thompson, Frost had been inspired to write the poem by Thomas’s habit of regretting whatever path the pair took during their long walks in the countryside—an impulse that Frost equated with the romantic predisposition for “crying over what might have been.” Frost, Thompson writes, believed that his friend “would take the poem as a gentle joke and would protest, ‘Stop teasing me.’”

That wasn’t what occurred. Instead, Thomas sent Frost an admiring note in which it was evident that he had assumed the poem’s speaker was a version of Frost, and that the final line was meant to be read as generations of high school valedictorians have assumed. The sequence of their correspondence on the poem is a miniature version of the confusion “The Road Not Taken” would provoke in millions of subsequent readers:  . . .

Continue reading.

Later in the essay, he writes:

The difficulty with “The Road Not Taken” starts, appropriately enough, with its title. Recall the poem’s conclusion: “Two roads diverged in a wood, and I— / I took the one less traveled by, / And that has made all the difference.” These are not only the poem’s best-known lines, but the ones that capture what most readers take to be its central image: a lonely path that we take at great risk, possibly for great reward. So vivid is that image that many readers simply assume that the poem is called “The Road Less Traveled.” Search-engine data indicates that searches for “Frost” and “Road Less Traveled” (or “Travelled”) are extremely common, and even accomplished critics routinely refer to the poem by its most famous line. For example, in an otherwise penetrating essay on Frost’s ability to say two things at once, Kathryn Schulz, the book reviewer for New York magazine, mistakenly calls the poem “The Road Less Traveled” and then, in an irony Frost might have savored, describes it as “not-very-Frosty.”

Because the poem isn’t “The Road less Traveled.” It’s “The Road Not Taken.” And the road not taken, of course, is the road one didn’t take—which means that the title passes over the “less traveled” road the speaker claims to have followed in order to foreground the road he never tried. The title isn’t about what he did; it’s about what he didn’t do. Or is it? The more one thinks about it, the more difficult it becomes to be sure who is doing what and why. As the scholar Mark Richardson puts it:

Which road, after all, is the road “not taken”? Is it the one the speaker takes, which, according to his last description of it, is “less travelled”—that is to say, not taken by others? Or does the title refer to the supposedly better-travelled road that the speaker himself fails to take? Precisely who isnot doing the taking?

Written by Leisureguy

20 August 2015 at 12:30 pm

Posted in Writing

BBS with Edwin Jagger, Shannon’s Soap, and Chiseled Face brush

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SOTD 20 Aug 2015

A very fine shave indeed, and the Edwin Jagger head is not to be sneezed at.

I really like the Chiseled Face angel-hair synthetic brush a lot. The handle is interesting, classy, and comfortable, and the brush performs well and feels good. I got an excellent lather from Shannon’s Soaps Barbershop shaving soap.

I have moved the Edwin Jager back up in the rotation because using it recently reminded me what a truly excellent design it is: quite comfortable and quite efficient, easily delivering a BBS result without any trace of a nick or problem. (I am eagerly awaiting a nick so I can try the alum trick: holding the alum bar in place against the nick for a while.) Although the Parker 24C is a smidge more comfortable and efficient (at least for me), the Edwin Jagger has the benefit of standard threading, so swapping handles is not a problem, and the EJ handle can also be used with another (standard-threaded) head. The Parker’s threads seem to have drifted off standard, or they are using a different standard.

A good splash of Woods from Saint Charles Shave, and the day begins.

Written by Leisureguy

20 August 2015 at 10:41 am

Posted in Shaving

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