Physics Is Erasing Your Memory

  • By Greg Kestin
  • Posted 07.25.18
  • NOVA

You might store your precious memories in diary passages or in photos backed up on a hard drive. But thanks to physics, no memory can last forever—not in a diary, not in a hard drive, not even in your brain. If you could live forever, you would eventually forget everything. Find out why in this episode of What the Physics?!

Running Time: 04:53


Physics Is Erasing Your Memory

Published July 25, 2018

Greg Kestin: So, I have a torch and some neodymium magnets. Let's see what happens when I heat them up.

So, these were magnets...until we heated them up—and they forgot. The same phenomenon that made the magnets forget that they were magnets ensures that no memory is permanent and even you will forget everything you ever knew.

Oh, by the way, did you turn off the oven? It's a simple yes or no. I know, sometimes you can't remember. Maybe what you need is a little switch—something where it says, "Yes, I turned it off" or "No, it's still on." 'Cause that would be a simple way to remember one single bit of information, whether it's good-bad, yes-no, or one-zero. But what if you wanted to store many pieces of information, like the information that's encoding this video, which is 1 gigabyte? That's 8 billion ones or zeros. Eight billion little switches would be the size of Manhattan if you put them right next to each other.

Luckily, we store information in a smaller kind of switch. So, in a hard drive, we have small magnets whose north poles point up for one or down for zero. There are actually several trillion magnetic switches in here. But why aren't hard drives even smaller? It's because the microscopic world is a dance party, with molecules bumping and jiggling. Here are some pollen grains in water—and scientists thought the pollen was actually alive, until Einstein proved that it was just water molecules that were hitting it and making the pollen grain dance.

And just like the water, the molecules in the hard drive are bouncing and jiggling and they're making those little magnets bounce too. And that's sort of a problem because they could eventually jiggle and flip over. And if that happens, then we lose the information that that single magnetic switch was holding. And that's what happened when I heated the magnets with the blowtorch.

Each of those magnetic balls is made of many small magnets, which are all pointing in the same direction—until you heat it and the microscopic bumping increases, flipping over some of those magnets and de-magnetizing the ball. If you tried to make a hard drive with even smaller magnets than we currently use, then that flipping over could occur at room temperature fairly quickly and they could lose their information in a matter of days.

Current hard drives can only hold information for about 200 years. So, what does this have to do with information in your brain? Your memories?

When you remember something, a particular sequence of neurons is triggered. An electrical signal travels down one neuron over a small gap to the next neuron, and that signal continues along the neurons until all the neurons that are related to that one memory have been triggered.

So, that little space between neurons? That's called a synapse and that controls whether or not the signal can travel from one firing neuron to its neighbor. And that signal can only cross if there are enough of a certain kind of molecule at that first neuron. Those molecules are called neurotransmitters.

The problem is that, over time, microscopic bumping can push those neurotransmitters out of place, preventing the signal to go from one neuron to the next. So, if you're trying to remember something but one link in that chain of neurons is missing, you won't be able to get to the rest of the memory.

On a day-to-day basis, there are other mechanisms that can cause you to forget. Things like similar memories interfering with each other and the presence of a different kind of neurotransmitter that actually makes you forget instead of remember. But if we could live much longer, or if you went into cryogenic sleep for centuries, then every memory you have would become dislodged because all of this bumping would knock neurotransmitters out of place. It's all because of this little microscopic party.

And, like any party, it makes you forget. And the cool thing forget.

By the way, the loss of data from bumping doesn't just affect brains and computers. It affects words that you write down, because the ink can actually be bumped out of place. And it affects DNA, which is why—I'm so sorry to say this—finding dinosaur DNA is actually impossible.

Oh, I remembered: subscribe. That's what it is. Yes, thank you. Subscribe.



Host, Producer
Greg Kestin
Research, Writing
Samia Bouzid
Greg Kestin
Filming, Editing, and Animating
Greg Kestin
Scientific Consultants
Murti Salapaka
Saurav Talukdar
Abu Sebastian
Editorial Input from
Julia Cort
Ari Daniel
Filming, Writing, and Editing Contributions from
Lauren Liebhaber
Daniel Thomson
Media: Shutterstock, CytoViva
Brownian Motion Footage courtesy of Sam Snook of Latimer Arts College
Special thanks
Entire NOVA team
From the producers of PBS NOVA © WGBH Educational Foundation
Funding provided by FQXi
Music provided by APM

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