Gravitational Potential Type Detectors

A project log for Low Cost, Time-of-Flight Gravimeter Arrays

Gravimeter array imaging requires building low cost, high sensitivity, time-of-flight (aka high sampling rate) sensors.

richardcollinsRichardCollins 04/11/2019 at 17:050 Comments

This project's immediate goal is low cost acceleration field measurement and imaging techniques. 

But the gravitational potential changes the rate of clocks, nuclear and chemical processes, at the surface of the earth - particularly, because of the changing distances and orientations of the sun, moon, earth and many things on earth.  These "direct potential" instruments derive from resonance measurement on the electronic and magnetic states of atoms - cesium and rubidum as a start - for use as precise atomic clocks.  As such they found the that clocks do change their rate at rest because of the absolute value of the gravitational potential (the acceleration is just the gradient of this potential), and can be "inverted" to report on the potential itself.

Mossbauer effect (very precise accounting for recoil energies during state changes in atoms and molecules with narrow linewidths) can be used to measure the gravitational redshift, which depends on an integral of the potential between two points.  His innovation was to find materials where the lattice surrounding the emitting (and absorbing) atoms (molecules) could absorb the recoil energy on the timescale in which the state change occurs.  That is difficult because finding and characterizing materials to have precise atomic and nuclear properties is hard for bulk materials.

With laser tools and fast ADCs and computing, it should be possible to use a wide variety of paired emissions and absorptions where the recoil can be tracked, accounted for, and compensated for.  There should be cyclotron versions and microwave plasma versions as well.  I am reviewing all those methods and possibilities, and will report later, or as I have updates.

The importance of the gravitational potential detectors, is there are broad classes of instruments and experiments being proposed, just started, or going on, sensitive enough that they need to account for (1) earth tides, (2) small variation in station location, (3) changes in the rates of atomic and molecular rates, frequencies, and energies due to the changing potential due to the sun and moon relative to the station. The earth itself is changing shape, and its potential changes are tracked by the International Center for Global Gravity Field Models (ICGEM),, along with its temporal variations.

This last affects many Bose Einstein condensate, quantum, superfluid, plasma and nuclear experiments.  I am trying to lay out the general rules, but my advice is that if you are saying "nano" and starting to whisper "pico" and "femto" and "atto", you need to check your local gravitational potential and acceleration field "weather report".  :)

Now it is a general rule of thumb, that any system that has to account for these types of changes, can invert their models for correction to become reporting nodes in a global network of sensors.  Sensor monitoring the positions of the sun and moon, and the shape and gravitational events on the surface of the earth and in the solar system.  So if someone's G experiment is giving them fairly wide variation from place to place, and time to time, it might well be they have not accounted for the sun, moon and earth portions of the potential and its gradient.

I do not know exactly how the signal is initated and travels from where the change is made, to "direct potential" or gradient sensors.  For a pendulum swinging nearby, used as a reference source, or just keeping video tracking and identification senors on poles of the nearby highway to identify them and correlate with gravity signals. Or using 3D video and imaging to get the shape of the ocean to calculate its gravity signal at your site.  All of these are quite complex.  Easy to do, but with noise and careful work required. The signals travel at the speed of (light and gravity) so you need to sample at rates appropriate to your needs.  If you want to use a gravity array to image ocean waves, it might need to be 1 cubic centimeter.  Is that possible?  Before all these new technologies, and the price of sophisticated measurement dropping, I might have said it will be decades.  But now maybe it will be much quicker.