A Proton Like a Falling Brick

John Walker:

The University of Utah operates a cosmic ray detector called the Fly's Eye II, situated at the Dugway Proving Ground about an hour's drive from Salt Lake City. The Fly's Eye consists of an array of telescopes which stare into the night sky and record the blue flashes which result when very high energy cosmic rays slam into the atmosphere. From the height and intensity of the flash, one can calculate the nature of the particle and its energy. On the night of October 15, 1991, the Fly's Eye detected a proton with an energy of 3.2±0.9×10²⁰ electron volts. . . .

The maximum energy the Large Hadron Collider at CERN can give to a proton is around 7 x 10¹³ electron volts, 5 million times less. This one proton was carrying enough energy to make a serious impact in the realm of big objects like you and me:

equivalent to 51 joules—enough to light a 40 watt light bulb for more than a second—equivalent, in the words of Utah physicist Pierre Sokolsky, to “a brick falling on your toe.” The particle's energy is equivalent to an American baseball traveling fifty-five miles an hour.

Since the energy of a particle is related to its speed through the formulae of special relativity, we can calculate the speed of this proton as 0.9999999999999999999999951 of the speed of light, or only 1.467×10⁻¹⁵ meters per second slower than light.

Now recall that the faster things are traveling, the more slowly time passes for them. If you could accelerate yourself to this speed, time would pass very slowly for you indeed. Walker calculated perceived travel times from the Earth to various points at this speed.

Object	Distance (light years)	Perceived Travel Time
Alpha Centauri	4.36	0.43 milliseconds
Galactic nucleus	32,000	3.2 seconds
Andromeda galaxy	2,180,000	3.5 minutes
Virgo cluster	42,000,000	1.15 hours
Quasar 3C273	2,500,000,000	3 days
Edge of universe	17,000,000,000	19 days

So at the speed of this proton, you would reach the edge of the universe in what seemed like less than three weeks to you.

The universe is strange beyond our imagination.