Modern observations can reveal gas, dust, and stars in the optical, ultraviolet, and near-infrared from most observatories on Earth. Both M51 and its companion display fascinating extended properties. But a century ago, we didn’t even know whether objects like this were galaxies or something else, like proto-stars in the process of forming. Debating didn’t exactly help resolve the issue. (ADAM BLOCK / MOUNT LEMMON SKYCENTER / UNIVERSITY OF ARIZONA)

Only Evidence, Not Well-Crafted Arguments, Can Settle Scientific Debates

It’s 100 years since astronomy’s famous ‘great debate.’ We still haven’t learned the most compelling lesson of all.

So, you’ve arrived at a crossroads: you think the world works in a certain way, and someone else disagrees with you and thinks the world works in a different way. You’ve both got your reasons as to why you’re convinced that your way is right and the other person is wrong, but for some reason, you cannot come to an agreement with one another.

In most arenas of life, you’d rightfully chalk this up to a difference of opinion. But in science, opinions don’t really matter: the world and Universe really do behave in a particular fashion. Either your conception of how the world works agrees with reality, in which case it’s valid, or it doesn’t, in which case it isn’t. Yet scientific arguments and debates happen all the time, even though they never settle anything. The only solution that’s scientifically valid is to obtain the critical evidence: a lesson we all need to be reminded of.

Heber Curtis (L) and Harlow Shapley (R) argued their positions on the nature of spiral nebulae, with Curtis arguing for a galactic origin and Shapley arguing for a proto-star origin. (THE ROCKEFELLER UNIVERSITY)