Deep into that Darkness Peering

The LUX dark matter experiment. Credit: Sanford Underground Research Facility


Mar 28, 2017

Dark matter detection failed again.

It was once thought that burned-out stars or large planets exert “dark” forces on galactic structures. Those invisible influences were called MAssive Compact Halo Objects (MACHOs). However, years of investigation found nothing. This led researchers to acknowledge that MACHOs are not dark matter candidates.

Weakly Interacting Massive Particles (WIMP) were the chief competitor with MACHOs for several years. Since no MACHOs were detected, physicists hope that a subatomic particle can account for the necessary gravity they say is caused by dark matter. The Cryogenic Dark Matter Search (CDMS) built a detector that was supposed to “see” WIMPs interacting with other atomic particles. It saw nothing, so it was upgraded to the SuperCDMS.

The SuperCDMS sensor is an array of germanium crystals cooled by liquid helium to a temperature close to absolute zero. Theory says that when subatomic particles strike an atomic nucleus in one of the crystals it is interpreted as ionization and heat—any tiny vibrations caused by an impact are seen as “hits.” However, SuperCDMS is plagued by false readings from cosmic rays and other ionized particles. After 12 years nothing indicates that WIMPs are colliding with the detector.

Previous Picture of the Day articles argue against dark matter. It is supposed to be undetectable, except through its gravitational interactions with baryonic, or “normal” matter. Each experiment over the years confirms that it is undetectable (non-existent?).

For example, the Axion Dark Matter Experiment (ADMX) uses a superconducting magnet. It is thought that axions should rebound off the eight Tesla magnetic field that the device generates. Supposedly, photon emissions can be “seen” by an antenna since the rate of microwaves is thought to be proportional to the axion decay rate.

Axions are said to be responsible for breaking “charge-parity symmetry”. It is not the point of this article to address the assumptions of quantum mechanics. Axions are hypothetical particles predicted by nuclear physics. Researchers say that they might exist, but “probably have no bearing on the hidden mass” of the Universe.

ADMX is plagued by the same difficulties as SuperCDMS. All electronic devices generate signals in many frequencies, so they create noise that ADMX must filter out. Earth’s magnetic field also fluctuates because of the Sun’s electromagnetic input. Temperature changes are noisy, since heat radiates infrared light. Despite the 4.2 Kelvin cold environment, tuning the detector continues to be impossible.

The Large Underground Xenon experiment (LUX) uses 368 kilograms of liquid xenon,1.6 kilometers beneath the Black Hills of South Dakota, as a “scintillator”. Photomultiplier tubes that are so sensitive they can detect a single photon surround the tank of xenon in the LUX experiment.

Dark matter particles are called “weakly interacting” because the weak force is influential over a distance smaller than a single nucleon (proton or electron). A dark matter particle would have to directly collide with an atomic nucleus in order to leave any sign of its passage. Since solid matter is mostly empty space, dark matter interactions would take place only once in uncounted trillions of trillion atomic nuclei. Thus the need for larger instruments containing more detection materials.

As Electric Universe author and speaker Wal Thornhill wrote:

“…when astrophysicists turn to particle physicists to solve their intractable problems and particle physicists use it as an excuse for squandering billions of dollars on futile experiments, neither party recognizes that the other discipline is in a parlous state.”

After an extensive (and expensive) upgrade, over the last 20 months LUX found nothing.

Stephen Smith

With apologies to Edgar Allen Poe

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