OT: Another dark matter candidate

If heavy gravitons exist, wouldn't we hear them? Like brownian motion. It would be noisy.

But we don't hear Brownian motion. It's just random noise.

One in a 21.5km cube isn't many, and a nanogram isn't all that heavy. Dark matter isn't supposed interact with normal matter, except gravitationally, so it wouldn't do much as it went through you.

This is charged dark matter, and neutral pair of charged particles might interact electrically - it presumably would have a dipole moment - but they might have a preference for clumping into fours and quadropole interactions are even shorter range than dipole interactions.

Presumably they'd have stellar velocities so they'd be travelling quite fast - the Sun's orbital velocity around the galaxy is about 230km/sec so they'd take perhaps 130usec to get through you.

If you spend maybe half an hour in a really good anechoic chamber, you will hear Brownian motion. I've done it, at Bell Labs.

Human eyes and ears operate close to quantum limits.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

One of the microphone designers at Knowles once told me that about half the noise in their best microphones came from Brownian motion and the rest from electrical noise. Their "quiet room" at the factory was a large (about 1 cubic foot) block of steel with a very small test cavity. It sat on an inflated rubber ring. I have been in a few large anechoic chambers. The quietest one which was at the Royal Signals and Radar Establishment claimed a noise floor of something like -10dB(A). All I could hear was my heartbeat and turbulence in the blood flow near my ears. That particular chamber consisted of a 5m cubic concrete box with

I don't understand that statement. Brownian motion is manifest as noise cause by random motion of the air molecules and we can hear it if it is amplified enough.

A standard test for noise in a ribbon microphone consisted of removing the magnet; the noise level dropped due to the removal of the Brownian noise from the air molecules striking the ribbon. The residual noise ('Johnson noise' plus amplifier noise) was considered adequately low if the total noise power dropped by 3dB when the Brownian component was removed.

Large-diaphragm microphones exhibit less Brownian noise then small-diaphragm ones because they average-out the random motion (3dB improvement every time the area is doubled).

The one at Bell was similar, a giant room with a wire mesh floor midway up. It had a mild trampoline feel. Walking in was like being drowned in liquid silence.

Seems like a multiple-element mike could decorrelate Brownian noise. Electrical noise too.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Yes. Measurements at the RSRE anechoic chamber were done using a

I have been in a magnetically shielded room at PTB in Berlin, at least at that time the magnetically quietest place on earth. IIRC 7 layers of MuMetall + other stuff, and big enough for some people. They used it for contactless measurement of brain currents with SQUID arrays.

Cheers, Gerhard

They need to update their web site a bit, or they don't seem to have noticed that the kg *has* been redefined in terms of natural constants since 2019.

Jeroen Belleman

A large diaphragm area has the same effect because the noise is random in space as well as time, so its effect on each square millimetre of diaphragm area is not correlated with the effect on the other square millimetres of area. Using a multi-element mic has exactly the same effect with regard to the noise but, depending on the way the elements are configured, can give various correlations of the wanted signals to produce the required directional effects.

I have used rows of cheap cardioid capsules, each with a small diaphragm area, to give the equivalent of a large diaphragm and low noise. A large circular diaphragm suffers from phasing effects if the performers aren't close to the axis. By stacking the capsules vertically I minimised the directional phasing effect in the horizontal plane at the expense of increased phasing in the vertical plane (where it doesn't matter as much).

Ears do a hardware realtime Fourier transform as well as time differential response to any sort of sudden click. Music appreciation and predator/prey to avoid/stalk respectively.

Off axis the eyes are a lot more sensitive but with less resolution and very sophisticated local motion detection. Astronomers call it using averted vision - looking directly at the target you have high resolution with colour if it is bright enough and off axis you have near quantum limited monochrome detection with about 1/4 the resolution.

If you spend a few hours in a darkroom you see random colour noise patterns and any light leaks due to imperfect blackouts. High quality darkrooms have black velvet lined folded back entry with three sets of doors.

I have been in the one at Salford which is only a single level of deep isolation with slightly longer foam wedges and a suspended fabric mesh floor. I can just about hear my own pulse in truly quiet locations.

It became quite loud after a few minutes in the anechoic chamber with the door shut and surprisingly hard to balance with the ears deprived of any acoustic echo cues. You don't realise what is missing until it isn't there. When they closed the door it suddenly went a *lot* quieter.

The sound of the sea you hear in seashells is another manifestation of random noise from Brownian motion (no relation) in a high Q echo chamber.

Yes, it would be kind to notify the web master :-)

Actually, they have described the whys and hows of the transition process in detail somewhere else; that page seems to be untranslated even in the English branch.

I'm not in the position to complain, my web site is unchanged > 15 years..

Cheers, Gerhard

I have phosphenes, a continuous background light show, with some moving structures. I had a medical event where they went away for a couple of days. It was really weird being in the dark. Boring.

I have occasional migraine auras too, without the headache.

Astronauts see cosmic rays.

I think some people see stuff during an MRI. I don't.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Largely because the original platinum reference kilogrammes were slowly evaporating (or otherwise losing mass). I confess that I am amazed that they can define the kg in this way with sufficient precision.

In truly dark conditions I am aware of the coloured noise in my fovea and the brighter halo in peripheral vision. A deer stumbled into me once when I was observing in Zion canyon - that was a surreal experience.

I'm not sure which of us was more surprised. The sky there is incredibly dark but the mountain silhouettes are darker still.

That is Cherenkov radiation. The refractive index of the medium of the eye means the particle is travelling faster than the speed of light. It creates a shockwave that dissipates kinetic energy as light.

The eerie blue glow in cooling ponds is another example of that.

They may get deafened but I'd be surprised if they saw things. The sounds from outside the MRI enclosure are quite alarming!

I worked on data reduction methods for them once upon a time. The mathematics is very similar to aperture synthesis radio telescopes.

There's nothing quantised about the noise from Brownian motion. But if heavy gravitons contributed background noise they'd be just another random noise source.

And if the air was disturbed by passing heavy gravitons it would still be random noise. What we hear is random noise - we attribute it to Brownian motion, but nothing in what we hear allows us to work out where the noise is coming from.

You do make my point.

A sensitive microphone in a chamber which could be evacuated or filled with different gasses at different temperatures would soon reveal if there was a component in the Brownian noise caused by something other than the thermal agitation of air molecules. Are you saying nobody has thought of this?

I don't see how gas-swapping would do any more than change the amplitude of the noise.

A soon as you get into non-random noise - 1/f noise perhaps - you'd have more data to play with, but it still wouldn't tell you all that much.

If you wanted to find a heavy graviton, baths of liquid argon might have more to offer.

A charged graviton presumably wouldn't stayed uncharged for long, and whatever it coupled up would create a sort of molecule with interesting properties. The heavy graviton is very heavy indeed for a single particle - about one nanogram if the theoreticians are to be taken seriously, but that shouldn't stop you calculating the partition function for the "diatomic" molecules created, which would give you their vibrational frequencies.

I can't imagine that it could stay partnered with anything except a heavy graviton of the opposite charge, but that says more about the limits of my imagination than anything useful.