kottke.org posts about Sean Carroll

Ten things everyone should know about timeDec 06 2011

From Sean Carroll at Cosmic Variance, a list of facts and very strong opinions about the nature of time.

4. You live in the past. About 80 milliseconds in the past, to be precise. Use one hand to touch your nose, and the other to touch one of your feet, at exactly the same time. You will experience them as simultaneous acts. But that's mysterious - clearly it takes more time for the signal to travel up your nerves from your feet to your brain than from your nose. The reconciliation is simple: our conscious experience takes time to assemble, and your brain waits for all the relevant input before it experiences the "now." Experiments have shown that the lag between things happening and us experiencing them is about 80 milliseconds.

5. Your memory isn't as good as you think. When you remember an event in the past, your brain uses a very similar technique to imagining the future. The process is less like "replaying a video" than "putting on a play from a script." If the script is wrong for whatever reason, you can have a false memory that is just as vivid as a true one. Eyewitness testimony, it turns out, is one of the least reliable forms of evidence allowed into courtrooms.

Rules for time travelersMay 20 2009

Sean Carroll lays out the rules for time travel for movies (but also more generally) based on our current understanding of physics.

1. Traveling into the future is easy. We travel into the future all the time, at a fixed rate: one second per second. Stick around, you'll be in the future soon enough. You can even get there faster than usual, by decreasing the amount of time you experience elapsing with respect to the rest of the world -- either by low-tech ways like freezing yourself, or by taking advantage of the laws of special relativity and zipping around near the speed of light. (Remember we're talking about what is possible according to the laws of physics here, not what is plausible or technologically feasible.) It's coming back that's hard.

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