eli5 Why can human embryo’s be frozen but not human adult?
In: Biology
The bigger a living organism is, the harder it is to freeze it quickly enough to not permanently damage it.
This is because, generally speaking, you can only cool the surface of something, but you have to cool its whole volume.
If you have something that you can freeze and you make it twice as big, the new, bigger thing has ~8x the amount of material to cool, but only ~4x the surface area to cool it with. So it’s effectively twice as hard to cool down.
This just gets worse and worse as you get bigger and bigger. Freezing an embryo is thousands of times easier than freezing a grown adult. There were experiments decades ago where hamsters were frozen and revived, but that’s about as large as can be done with living things on Earth.
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