Inhuman Distances

Today, inhuman distances. The University of Houston presents this program about the machines that make our civilization run, and the people whose ingenuity created them.

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   The speed of light is a difficult thing for humans to grasp. 186,282 miles per second seems so absurdly fast it might as well be instantaneous. But imagine for a moment that you have a magic laser pointer. Point it east and it will circle the earth, its beam shining on you from the west. Pretend there is no air in the way of our light beam. In this scenario, the red dot will appear on your back approximately 1/8 of a second after you press the button. So, light speed is not quite instantaneous. To put it in musical terms, that eighth of a second it took to circle the globe is a sixteenth note at march tempo, 120 beats per minute. Think of the opening of Mozart’s Turkish March. Now cut everything except the first two notes. The time between those two notes is your eighth of a second. The speed of light now seems remotely human.

     But when we ask light to measure larger distances, its astonishing velocity again becomes unfathomable. For example, the James Webb space telescope is now seeking biosignatures. These are chemical signs of life on exoplanets, planets orbiting other stars. In the constellation Leo, on an planet coldly named K2-18b, the telescope has detected methane and carbon dioxide in the planet’s atmospheric spectrum, along with hints of water vapor. These could be signs of biological life. 

Artist's impression of K2-18b (right) orbiting red dwarf K2-18 (left); the small crescent in the middle is K2-18c in planetary phase - Wikipedia

And, this planet is only 124 light years away, not millions of light years like some stars and planets. 124 years seems human enough. After all, a handful of people have lived nearly that long, and we have grandparents or great-grandparents whose birthdates go back twelve decades. So let’s do some math. The space probe Voyager 1, launched in 1977, has been traveling for nearly 50 years, at a speed of 38,000 miles per hour. In 2026 Voyager will achieve a milestone: it will have finally reached the distance light travels in one day. To get to our mystery planet, multiply that half-century in space by 365 days times 124 years. At that rate, it will take Voyager over two million years to reach K2-18b. We have of course achieved speeds far greater than Voyager, but it doesn’t help much. Increase Voyager’s speed by a factor of twenty, for example, and the trip would still take over 100,000 years. And then to slow down enough to take a proper look at this planet? That would require as much energy as it did to get there. The speed of light, and the immense, inhuman distances it represents, may ultimately crush our dreams of interstellar travel. But, take heart, we still have our human scale of time and space. And, we still have Mozart.

   I’m Roger Kaza, from the University of Houston, where we’re interested in the way inventive minds work.

[Mozart’s Turkish March]

The debate over whether light has a finite speed or is instantaneous goes back to the ancient Greeks. Danish astronomer Ole Rømer first demonstrated that light has a finite speed in 1676 by observing delays in the eclipses of Jupiter's moon Io, showing light takes time to travel across Earth's orbit.

The “magic laser pointer” is magical because the earth’s gravitational field is not strong enough to bend a laser light around the planet. We also pretend our trip is an equatorial distance of approximately 25,000 miles, and pretend there is no air, because light travels at 186,282 miles per second only in a vacuum, and is slower in other mediums like air, water or glass.

Voyager’s 38,000 miles per hour speed equates to 10.5 miles per second, something like .005% of the speed of light. To drive to K2-18b at highway speeds? About 800 million years. To walk? You do the math. Hint: much longer than the universe is old.

Wikipedia article on K2-18b: https://en.wikipedia.org/wiki/K2-18b

More on K2-18b https://www.bbc.com/news/articles/c39jj9vkr34o

A less pessimistic view of interstellar travel, albeit with unmanned, tiny probes: https://www.astronomy.com/science/breakthrough-starshot-a-voyage-to-the-stars-within-our-lifetimes/

Mozart performed by Wilhelm Kempff. The Turkish March is the final movement of Mozart’s Sonata No. 11 in A major, K. 331.

Thanks to a Facebook post and Reddit commenters for the inspiration of this episode.

This episode first aired January 27, 2026.