August 31, 2004


Scaled-Up Darkness: Could a single dark matter particle be light-years wide? (George Musser, 8/30/04, Scientific American)

In 1996 Discover magazine ran an April Fools' story about giant particles called "bigons" that could be responsible for all sorts of inexplicable phenomena. Now, in a case of life imitating art, some physicists are proposing that the universe's mysterious dark matter consists of great big particles, light-years or more across. Amid the jostling of these titanic particles, ordinary matter ekes out its existence like shrews scurrying about the feet of the dinosaurs.

This idea arose to explain a puzzling fact about dark matter: although it clumps on the vastest scales, creating bodies such as galaxy clusters, it seems to resist clumping on smaller scales. Astronomers see far fewer small galaxies and subgalactic gas clouds than a simple extrapolation from clusters would imply. Accordingly, many have suggested that the particles that make up dark matter interact with one another like molecules in a gas, generating a pressure that counterbalances the force of gravity.

The big-particle hypothesis takes another approach. Instead of adding a new property to the dark particles, it exploits the inherent tendency of any quantum particle to resist confinement. If you squeeze one, you reduce the uncertainty of its position but increase the uncertainty of its momentum. In effect, squeezing increases the particle's velocity, generating a pressure that counteracts the force you apply. Quantum claustrophobia becomes important over distances comparable to the particle's equivalent wavelength. Fighting gravitational clumping would take a wavelength of a few dozen light-years.

That would be a case of art imitating art.

Posted by Orrin Judd at August 31, 2004 1:33 PM

Sounds like someone has been reading Tom Van Flandern again.

Posted by: Raoul Ortega at August 31, 2004 1:42 PM

Isn't "Bigons" the name of the men's magazine Al Bundy used as bathroom reading material?

Posted by: Rick T. at August 31, 2004 3:39 PM


No, it's "Bigguns".

Posted by: Annoying Old Guy at August 31, 2004 3:47 PM

Apparently Orrin thinks this is another example of the frivolous "science" predicted by John Horgan.

Time will tell. I admit I just don't "get" the concept of weakly interacting massive particles.

Neutrinos, I have no problem seeing them zipping through me and the earth all the time. They have practically no mass, they're infinitesimally small. And we are mostly empty space anyway (especially between the ears, har har.)

But sizeable massive particles, bumping into us and yet not bumping into us?

Guess I'll have to wait a few decades until a brilliant popularizer comes along who breaks it down into bite-sized chunks that I can integrate into my intuition.

Posted by: Eugene S. at August 31, 2004 3:50 PM


Intuition? You're joking right.

Posted by: oj at August 31, 2004 5:07 PM

This is an intriguing theory. To have a wavelength of a few dozen light-years (~10^19 cm), the particles would have to be extremely light -- about 1/10^27 the mass of the electron. To account for the missing mass, our Milky Way would have to contain about 2 trillion solar masses of these particles, or about 4x10^42 g, or about 4x10^69 electron masses. In other words, about 4x10^96 of these particles in the Milky Way. The volume of the Milky Way is about 10^13 cubic light years; so there must be about 4x10^83 of these particles per cubic light year. Since each particle occupies about 7000 cubic light years, that means that any point in the Milky Way has on average 3x10^87 of these particles overlapping it. In otherwords, our bodies fall within about 10^87 of these particles.

Lucky these particles (if they exist) don't interact with matter, or we'd find the earth mighty crowded.

Posted by: pj at August 31, 2004 5:17 PM


Posted by: oj at August 31, 2004 5:47 PM

pj, the hypothetical WIMPS do interact with matter, as their name indicates.

And everwhere is as crowded as the head of a pin.

The quill from a buzzard
The blood writes the word
I want to know am I the sky
Or a bird
'Cause hell is boiling over
And heaven is full
We're chained to the world
And we all gotta pull.

--'Dirt in the Ground' (Tom Waits)

Posted by: Eugene S. at August 31, 2004 5:47 PM

Mayhap his Orrinness will recall our little conversazione the other day when the topic of Relativity came up; in the course of which I had occasion to remark that our native intuition frequently is inadequate to model even the simplest mechanical problems, much less the Special Theory of Relativity.

I then begged your Excellency's indulgence for inserting a link to another website that in my insignificant opinion had well managed to illustrate the principles of SR, in a way at once accessible to a mere plodder's mind and conducive (this latter, I must confess, I neglected to mention) to being absorbed into the reader's intuition.

For it is my uniquely personal (and doubtless laughable) belief that we have only mastered a subject when it has become second nature to us, or part of our intuition.

Posted by: Eugene S. at August 31, 2004 6:04 PM

So, after laughing at the concept of a being we cannot see, but which interacts with us, the materialists suggest the existence of particles that we cannot see, but which interact with us.

Posted by: Ptah at August 31, 2004 6:26 PM


And it is my position that the social narrative creates your scientific intuition. Let this nonsensical idea, borrowed from a joke, hang around awhile and you'll teach it to your kids as obvious fact.

Posted by: oj at August 31, 2004 6:33 PM

social narrative creates your scientific intuition

I am neither the first, nor will I be the last, to note the irony that the post-modernist soi-disant philosophers of science on the far left and a hard-headed conservative New Hampshireman are twinned like peas in a pod.

Such convergence, however, is not automatically evidence that Mr. Judd is barking mad. Contrariwise the po-mo Gallophones may have backed by accident into a clearing hacked free by Orrin's machete of "universal skepticism".

We will have to continue monitoring the situation with utmost vigilance. Nurse Ratched, keep me updated please... and help me out of this jacket!

Posted by: Eugene S. at August 31, 2004 7:20 PM

Post-modernism is pre-modern.

Posted by: oj at August 31, 2004 7:36 PM

Eugene - They interact only through gravity, not the electromagnetic or nuclear forces (or, if they do interact by these forces, do it extremely weakly). Gravity is a very weak force; and the particles' gravitational pull is largely cancelled by other such particles, since they are distributed through space. Therefore, it's easy not to notice them.

To understand the "bumping" issue, you have to realize that:
(1) particles don't have hard edges; rather, they have wavefunctions, which you can think of as a probability distribution. The size of the particle "blob" is inversely proportional to its mass. The size of an electron is about 1 angstrom; the size of a proton is about 10^-3 angstrom - that's why the nucleus is so small, it's the size of the electrons that determines the size of the atom.
(2) You don't bump into particles, rather you feel the forces they exert. If the particles don't exert any forces (i.e., interact) then you have no way to "feel" their existence. You have a sense of "bumping" on a macroscopic scale only because the forces get much larger as you get close to particles. But if the particle is large enough and its forces are weak, then there's no sharp rise in force to "feel."

Posted by: pj at August 31, 2004 8:56 PM

This suggestion makes no sense at all. In analogy to a gas, you would have a uniform distribution throughout space, and there would be no gravitational clumping effect on the scale of galactic clusters. Yet the only reason for the hypothesis is to account for the unexplained clustering.

As pj's calcuation suggest, these would not be WIMP's but instead WIVLP's (weakly interacting very light particles), more like neutrinos than anything else.

Such bizzare suggestions indicate to me that the contradictions between quantum mechanics and general relativity are becoming critical and unresolvable.

Posted by: jd watson at August 31, 2004 10:15 PM

pj, I understand already that if my hand does not pass through a tabletop it is not because the atoms in my hand come up against the atoms in the table; rather, it is the electromagnetism keeping the two solid bodies apart from each other.

But of course naked particles can and do bump into each other: cosmic rays hitting the upper atmosphere, particle accelerators at Stanford and elsewhere.

What bothers me about the WIMPS is that if they are really this big - a lightyear across - then they would interpenetrate us, i.e., ordinary matter. But that violates the exclusion principle, namely that two particles cannot occupy the same position at the same point in time.

Posted by: Eugene S. at August 31, 2004 10:45 PM

Eugene S:
I thought the exclusion principle was that two fermions could not have the same quantum numbers, i.e., couldn't occupy the same quantum state. The atomic electron orbitals show that electron wave functions can occupy the same space.

Posted by: jd watson at September 1, 2004 2:06 AM

jd, you're right.

(hangs head in shame)

Posted by: Eugene S. at September 1, 2004 5:49 AM