Do similar laws of physics throughout the Universe imply that all life must be like life on Earth? (Beginner)

Hi, I'm an eleventh grade physics student and I have a few questions about extraterrestrial life. I have been thinking about this subject for a while, and I have a theory. Since the laws of physics apply to everything in the universe, then wouldn't the appearence and evolution of life on a space body follow the same pattern throughout the universe as well? For example, people use the phrase "life as we know it", meaning life with the same properties as life on earth. Wouldn't all life anywhere have to evolve the same way? Space creatures and monsters as seen in movies, in my opinion, are products of the human imagination, and if extraterrestrial life was ever found, it would include species such as mammals, reptiles, insects, and plants the same as the ones on Earth, and humans as well. Is this theory legitimate? I just think that all life would evolve the same way, and only under earthlike conditions. Thank you for your time.

It's an interesting idea, but I'm afraid I have to disagree. While the laws of physics are (to the best that we can determine) similar throughout the Universe, the characteristics a species develops through evolution do not spring directly from physical law. For example, imagine a planet like Earth, except that it orbits a reddish star, rather than a yellow-green one like our Sun. This solar system and our own can coexist under the same laws of physics, and yet life on the two planets would evolve to take the most advantage of the light provided by their respective suns (as in, sensitivity of vision vs. wavelength, color of plants, etc.). This is only one possible difference; you can imagine a whole range of possiblities, with the two planets differing in chemical composition, atomospheric composition, mass, eccentricity and period of orbit, etc., which would result in populations with very different characteristics.

What is more, neither do the characteristics of a species spring directly from its environment. For example, look at the vast array of creatures able to flourish in the same regions on Earth. I would argue that if two such disparate creatures as the tree frog and the parrot can evolve in the same region, then life even on two similar planets need not be very similar at all. With some imagination, one can even extend the argument to forms of life quite different from our own—that is, while carbon, oxygen, and water are very convenient for our own biological systems, they by no means exclude entire other systems that rely on other chemical reactions and molecular structures under other conditions, with which we are less familiar. The same idea can be applied to the ecological systems that govern the interactions among the various forms of life.

It's important to wonder about such things—with all of the interest in discovering extraterrestrials, we'll want to know what we've found if we run into one!

This page was last updated June 27, 2015.

About the Author

Sara Slater

Sara is a former Cornell undergraduate and now a physics graduate student at Harvard University, where she works on cosmology and particle physics.

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