The Fifth Force at Index

[Sherri]

For those who always wondered why the climbs at Index feel hard...

 

We were looking for shade over at the Country yesterday and it looked like a yard sale was going on by the tunnel:

 

They left the door open:

 

So we crept in for a closer look:

Light wasn't good enough to take a pic inside, but it basically looked like a beer-making set up, with tubes and beakers and whatnot.

 

The folks from the UW Gravity Lab explained that they had been running tests there for the past 20yrs measuring the "Fifth Force"--something to do with gravity and atomic something or other--and now that the experiment is ended the tunnel will be emptied and sealed.

 

I expect gravity at Index will return to normal levels shortly thereafter. Climb on.

 

 

[ryanb]

I used to work in a lab next to some of the uw gravity guys.

 

Basically they use really delicate pendulums to check to see if gravity behaves oddly at shortish distances (~1 mm when i was there).

 

The idea, as they explained it at the time, was if string theory involves a lot of weird extra dimensions all wound up maybe the pendulum might interact with them. No string theorists seems to think this might happen but it is good to check these things.

 

The cool thing is that the pendulums were accurate enough that they could tell when the parking lot was full or the hillside outside was soaked with rain water by looking at the data and delicate enough that a jostle to the enclosure (or an earthquake) would break the wire it was hung by.

 

 

[Sherri]

The cool thing is that the pendulums were accurate enough that they could tell when the parking lot was full or the hillside outside was soaked with rain water by looking at the data and delicate enough that a jostle to the enclosure (or an earthquake) would break the wire it was hung by.

 

Interesting. I bet I screwed up their experiment by all the falling I did out there this summer.

 

They said the reason they chose that particular tunnel was because 1)it was there, and 2)they knew the exact mass of the granite pressing down onto it

[mountainmatt]

Too bad, it would have made a great "sit start" to Ultra brutal

 

 

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[olyclimber]

Are you sure it wasn't dudes cooking up some meth? LOL

[trumpetsailor]

There are essentially two groups working on gravity at UW - I work for the other one (at CENPA on campus). If you're curious about what they're doing in the tunnel, read on!

 

What's a fifth force?

 

So far as science is aware, there are only four forces: gravity, electromagnetism, the weak force (important to some nuclear decays/neutrinos, etc.), and the strong force (what really holds a nucleus together). Experiments like the ones done at Index are looking for tiny forces (weak, even compared to gravity) that would be due to some new physics we don't yet know about. If there is a grand unified theory to be found (one that tacks the theories of all four forces together into one package), then it's very likely that a "fifth force" exists, but it's going to be really feeble.

 

How do the experiments work?

 

These experiments are a search for materials that are pulled by gravity a little differently than their inertial mass would suggest. In everyday life, we're very accustomed to the observed fact that something with lots of inertia (hard to move if you push on it, even if it's on wheels) is also very heavy (gravity pulls on it hard). Physicists do not know why this is true. This notion, called the "equivalence principle", is a key foundation of General Relativity, but it's only based on observation. Searches for a fifth force, then, look for a gravity-like force that depends on the composition (protons, neutrons, feathers, yo mama, whatever) of a piece of matter but not its inertial mass. This Equivalence Principle turns out to be really true: If you drop any two materials in vacuum, experiments at UW have shown that the difference in their acceleration is less than ~0.0000000000003%.

 

Why Index?

 

The experiments done in the tunnel there look at forces that pull sideways (gravity attracts all things toward one another; it doesn't just pull "down"). It's therefore advantageous, for a gravitational experiment, to be near a huge cliff. That way, there's a whole lot of mass on one side of the experiment and you can test whether or not two materials are attracted differently toward it. It's also important to know what the cliff is made out of, since the strength of any observed fifth force will depend on the cliff's composition too. Furthermore, precision physics experiments like underground caves and basements where the temperature/environment is very stable.

 

I don't work in their lab, so I don't know for sure, but I wouldn't be surprised if the "Radioactive Materials" sign is there to discourage vandals. Most of the materials involved in gravitational research are as innocuous as tiny chunks of aluminum and titanium.

 

Thank you so much for helping to fund this kind of work (our lab costs about $0.003 per US taxpayer per year to run). On the good days, it's as good as putting up a first winter ascent. In return for funding basic research like this, occasionally you get things like GPS, which are pretty rad, and facts like those stated above.

[mattp]

One of the physics lab guys told me that the pendulum research had an application for submarine navigation. They could drive a nuclear sub to Japan watching the pendulum with their laser, and "map" the trip by recording how the pendulum was pulled by undersea terrain. They would make this trip while using the standard navigation equipment which would require use of signals detectable from orbit. They could then later repeat the same voyage without using the navigation equipment so no enemy satellite could detect where the sub might be going.

[num1mc]

What has been explained to me by Professors at the tunnel, which jibes with the above post by trumpetsailor, is that they are looking for "quantum gravity". Classical physics assumes that the effects of gravity are solely based on mass. These experiments want to see if there are basic differences in the effects of gravity based on the material. In other words, is the gravitational effect on a pound of lead different than on a pound of gold.

 

I am sure that the radiation signs are in reference to radon accumulations