Are We Meant to Leave Earth? Why Humanity May Have No Choice but to Go to Space
The Michael Shermer Show
Michael Shermer
4.3 • 1K Ratings
🗓️ 2 December 2025
⏱️ 94 minutes
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Summary
Astrobiologist Caleb Scharf joins Michael Shermer for a wide-ranging conversation about the past, present, and future of our relationship with space. Drawing on his new book The Giant Leap, Scharf explains why human expansion beyond Earth may be less a choice than an evolutionary development, and he walks through the physics, history, and personalities that shaped our journey off the planet.
Scharf also explains the biological toll of radiation and microgravity, and why terraforming Mars is probably unrealistic and why our future might rely more on building vast rotating habitats in space than on settling other planets.
Caleb Scharf is an astrobiologist and recipient of the 2022 Carl Sagan Medal. He was Director of Astrobiology at Columbia University in New York and is now the Senior Scientist for Astrobiology at the NASA Ames Research Center in Silicon Valley. He is author of more than 120 scientific papers and over 500 popular science articles. His new book is The Giant Leap: Why Space is the Next Frontier in the Evolution of Life.
Transcript
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| 0:00.0 | So on Earth, you know, if you went to a high enough mountain, |
| 0:04.0 | and let's say there wasn't any atmosphere because that just gets in the way, |
| 0:08.0 | and you fired off a bullet probably at around 8 kilometers a second, |
| 0:14.0 | eventually, if you didn't step out of the way, the bullet would come around and hit you in the back of the head. |
| 0:19.0 | Sort of 90 minutes later, or thereabouts, because the bullet would have vented an orbit. |
| 0:25.0 | On Mars, the dust is not only abrasive, it's also chemically quite reactive. |
| 0:30.3 | There are things called perchlorates that form on the surface of Martian soil, and they're |
| 0:34.7 | essentially oxidants, and they're pretty aggressive. It's like, |
| 0:38.5 | you know, putting your oven cleaner on your skin or in your lungs. A bullet that you just |
| 0:44.2 | drop out of your hand will fall at exactly the same rate as the bullet that you fire out of your |
| 0:51.0 | rifle. Of course, the bullet that you fire out of your rifle will travel |
| 0:55.1 | a greater distance horizontally, but the amount of time it will take to hit the surface |
| 1:04.9 | will be the same. A thought experiment of trying to go to Alpha Centaurite with a chemical rocket. |
| 1:11.7 | And it turns out if you want to do that in any reasonable amount of time, let's say 100 years, right? |
| 1:17.2 | You know, 100 years is commensurate with a human lifetime. |
| 1:20.8 | You could imagine building an enormous interstellar chemical rocket. |
| 1:25.1 | Well, it turns out that the amount of rocket fuel you would need |
| 1:29.1 | or propellant is some enormous factor greater in mass than the mass of the observable universe. |
| 1:36.6 | So you could build a chemical rocket and get Alpha Centaur know, 40,000 years, 50,000 years. |
| 1:44.2 | In fact, we've pretty much done that with the Voyager Prods. |
| 1:47.6 | But anything quicker than that, and chemical rockets are not going to get you there quickly enough. |
| 1:57.7 | All right, everybody, it's time for another episode of the Michael Shermer show. |
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