Blue Holes and Dark Matter

The National Geographic Society has organized a series of talks entitled, “The Big Idea” that each pairs a Nobel Laureate with a National Geographic Explorer of the Year to learn about each topic area and then explore common ground.  One of my fellow Fellows organized an outing to yesterday’s “Blue Holes and Dark Energy” event.

Kenny Broad is the explorer who investigates blue holes- water-filled caves carved out of limestone that exist at the interface of fresh water and salt water.  Because of the extremely slow rate of diffusion- an oxygen molecule takes eight years to go from the surface of the water down a foot- the debris in the caves stalagmites can be used in parallel with ice and core samples to investigate historical conditions on Earth.  The vast halocline, the transition zone between the lower salt water and the upper fresh water, is also an analog for ancient oceans and allows Dr. Broad to explore the origins of life.

The blue holes also allow for the exploration of the link between inland freshwater and oceanic saltwater.  Tires and a swing set dumped inland may appear in a cave a quarter mile out to sea.  As Florida is discovering vividly, a positive pressure of freshwater is vital to prevent saltwater incursions into the water supply, and as more freshwater is pumped and used, that balance becomes increasingly more precarious.

Last year’s Nobel Prize in Physics went to Adam Reiss, who discovered that the expansion of the universe is accelerating, which is largely attributed to dark energy.  He did an outstanding job of simplifying the ideas behind how we determine the distance to an object without actually going to that object.  Ships at sea used lighthouses; the brighter the light, the closer you are as long as visibility is good.  For those times when visibility is poor, fog horns can also provide an estimate of distance.  Surveyors use parallax and geometry.  All humans innately scale against a standard-sized object so that we know that the apparent size difference between a goose nearby and a goose far away is due to the increased distance.  Astronomers use variations on each of these methods to estimate the distance from Earth to the stars.

Dr. Reiss’s lighthouses or astronomical “standard candles” are supernovae viewed by the Hubble space telescope.  After establishing that the expansion of the universe was accelerating, he went on to point out that all of the known matter in stars, planets, gases, etc, amounts to a mere 4.5% of the matter in the universe.  Of the remainder, 23% is dark matter, and 73% is dark energy, about which we know very little at this point due to the limitations of our technology and mathematical theories.

Once each man presented an overview of his work, they sat down with a moderator and had an excellent discussion of where they had common ground.

They were first asked about how they reacted to an “ah ha!” moment.  In spite of the difference in their fields, they found their responses to be very similar.  The first reaction to a great discovery is, “Is this a mistake?”  Were the calculations correct?  Was the specimen identified correctly?  Is this observation an anomaly, which is to be discounted, or is it representative of a phenomenon?  The second step involves a lot of waiting.  In astronomy, the result must be verified by other groups and other methods, so a lighthouse distance result must be validated by someone using a fog horn or parallax method.  In cave diving, the specimen must be sent out, identified, classified, and checked against other databases to establish if it is a newly identified life form.

I was particularly intrigued by the relationship these two scientists have to time.  In cave diving, the team is trying to learn about how life evolved thousands or tens of thousands of years ago, but they are constrained by the amount of air in their tanks so that time on a dive ticks away relentlessly.  In astronomy, they examine light that has taken billions of years to arrive on Earth, but since the Hubble telescope receives ten years’ worth of proposals for every year of available time, experiments using the Hubble telescoped are choreographed down to the last second.

Both men agreed that good scientists don’t accept what they see at surface value; they want to explore further.  Apparently this habit of questioning everything is contagious.  Dr. Broad, the cave diver, explained that he will announce to his five- and nine-year-old children that it is time for bed, to which they respond, “Based on what theory?”

Finding common ground

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