Ask a Scientist

Courtesy of The University of Tennessee, Knoxville.

Let’s be real: It would be pretty cool if we could extend our lives for another decade or so despite an illness, or have the opportunity to be brought back to life after death. 

Imagine you could just go to sleep for 100 years, wake up in the future, and be totally fine – or at the very least be better. Seems like some pretty stellar science-fiction. Pretty sure that’s the premise of Samurai Jack actually. But is preserving a body and then reviving it possible? Maybe, but probably not right now.

First, we should mention that the word, “cryogenic” has some important historical context. A cryogenically frozen thing – person or otherwise – is something that has been put in very cold temperatures. NASA actually coined the term in the 50's. They also suggested that gases could be considered cryogenic if they “can be liquified at or below -240 degrees Fahrenheit,” or around -151 degrees Celsius.

So, nitrogen, the most abundant gas in earth’s atmosphere, becomes liquid below -320 Fahrenheit in our atmosphere and would therefore be considered cryogenic. Putting something into liquid nitrogen would therefore make it, if only for a few moments, cryogenic as well. This term can be useful for describing all sorts of things, like environments on planets. But within the last century, we’ve used the idea of something being “cryogenic” for preserving a person. Even though not everything that is cryogenic involves people.

Knowing this, a person that is being cryogenically frozen isn’t just being put into a typical freezer. Our freezers are nowhere near that cold. And there are a couple of interesting reason for this – it boils down to keeping the cells intact. First, dead tissues and cells decay, which is definitely a problem above freezing. If the thing you’re freezing doesn’t get cold quick enough, it could break down. Freezing also has to be even, otherwise the materials you’re freezing could physically bend and change into ways that are irreversible. Something that is sturdy might not have this problem, but something delicate like skin are susceptible to this.

But let’s say all of that is accounted for. Even the act of freezing can cause problems. Whenever you freeze anything, especially something that was alive, you have to worry about how ice forms. Ice is a solid after all. If tissue – which is comprised primarily of water – solidifies, the structures that keep the cell intact might actually be destroyed.

For instance, when a cell membrane in tissue ruptures, that cell is basically dead. While cells aren’t super delicate, they’ve got nothing on ice shards forming and piercing their membranes. You might have heard of the term “flash-freezing.” While it’s used mostly as a marketing for frozen vegetables and meats, the idea is the same, freezing something quickly helps preserve it and can affect its quality markedly.

Theoretically, you could account for those problems when freezing something and then revive them later if you did the freezing correctly. Physically, freezing quickly should help to preserve something that’s alive. But that isn’t the only technique you can use, nor is it all you need either. You may also need to use chemicals to affect how water freezes, either preventing water from turning into ice entirely, or affecting how water freezes. Scientists have coined the term “cryoprotectants” to discuss compounds which do just that, and this idea has been around for a long time. Glycerol is one many microbiologist labs use to protect the microorganisms being preserved from dying. Without it, even their very cold freezers wouldn’t effectively preserve the little guys.

So, the idea of doing it for a person isn’t totally crazy at first glance. Just freeze a person using a low temperature, under cryogenic conditions if you’ve got the ability, and maybe use some cryoprotectants along the way. Hence, the field of preserving people for revival was born, also know as, “cryonics.”

And yet despite decades of this idea being around, we’re still not sure if it can work or not. Why? Well, for one, no one has been cryogenically frozen and revived yet. Though we’ve had some luck with animals. One study revived a tardigrade, also known as a water bear, that had been frozen for more than 30 years. These animals probably aren’t the best representation for a person though. Water bears are tiny, less than a millimeter long, and they can be pretty resilient. Things that would kill other animals, like being put in space, don’t necessarily kill these little guys.

All of this is easier said than done. We can also imagine where some complications could pop up. First of all, a person isn’t just a slab of tissue or a group of bacteria. It’s got different tissues and cells which freeze and transfer heat at different rates. Muscle, fat, bone, organs – they’re all twisty and in complicated shapes. All of that affects how those parts of a body freeze with time; it’s just not the same as a little water bear, a slab of tissue or individual cells of bacteria.

So low temperatures might be able to freeze a person quickly enough and evenly enough, but it can be delicate, and we might need even lower temperatures than what’s traditionally provided at cryogenic conditions. Adding to the complexity, the brain is especially delicate and doesn’t freeze easily. Further, introducing cryoprotectants is also hard. To really be effective, a cryprotectant has to evenly coat the materials being frozen and become incorporated into all of the fluids in a person. How do you effectively replace all of the right fluid in a person with cryprotectants without adding additional medical complications? Good question, one that hasn’t been totally figured out. These problems make this whole reviving a cryogenically-freezing-person-ordeal a scientific challenge.

But the biggest one might be the legal requirements for cryonics. To cryogenically freeze a person, the person must be considered legally dead before being frozen. So, you can’t freeze a person that’s alive. No “Samurai Jack” scenarios allowed! Granted, someone could be “legally dead” without being biologically dead – but still, that scenario seems exceptional. Even if you preserve this person perfectly, you still have to bring an already dead person back to life, which is a pretty astounding proposition. Freezing a person just adds more problems to the equation.

Who knows if we can in the future. Maybe modern medicine will be able to revive legally dead people in more ways than we already know. Maybe our doctors don’t really have the most accurate grasp on what makes a person “dead” or not. But freezing people, even quickly, isn’t exactly a flaw-free premise. We don’t have a lot of perfectly preserved animals to use as a case study, which could have been frozen while alive. Right now, it’s hard to tell, but there are plenty of advocates out there hoping for the next biggest breakthrough anyway. That being said, there are far more opponents, and the science seems pretty clear on this one. It’s an unlikely pipe dream with the currently preserved people, and it’s definitely not possible now.

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