Robert Heinlein’s The Door Into Summer

Robert Heinlein’s The Door into Summer is a time travel SF novel published in 1957.

Syd Logsdon’s recent blog post at A Writing Life got me thinking about it again. One of the stand-out aspects of this novel is the time-travel physics, which is the best thought-out in SF that I can think of. It actually explains why, in a universe with time travel, people are not constantly inundated with throngs of tourists from the future.

But a precis first: The story starts in the future (from the point of view of 1957). The narrator and main character, Dan Davis, is an inventor. In this future society, time travel has not been discovered yet, but suspended animation is well-established, and people can take one-way trips into the future via this method.

Davis and his business partner fall in with a con artist named Belle. She’s vile, but I don’t have space to exposit the details of her perfidy. Long story short, she tricks Davis out of his share of the business, drugs him, and has him involuntarily put into cold sleep for a couple of decades.

There is another element here, a young girl called “Ricky” who doesn’t have much of a responsible adult in her life other than Davis, though they’re not related.

Davis wakes up thirty years in his future and is desperate to go back in time to take care of this child, but of course that’s impossible. Or is it?

Turns out a brilliant physicist has, in fact, proven that “temporal displacement” is possible, and has constructed equipment to move objects through time. The military has classified it and he’s not allowed to talk about it, but it does work, and Davis finds out about it. But there’s a catch. Oh my goodness, there’s a hell of a catch:

Time displacement is subject to quantum indeterminacy. You can decide on the length of your trip… but you can’t control whether you’ll go forward or backward! Want to set the dial for 50 years? Okay! Have fun in 2067… or maybe 1967.

Oh, sweet damn, that’s good. Ponder what Heinlein did here:

First, this is broadly consistent with the way the universe works on the quantum scale. I don’t mean that Heinlein learned quantum physics and worked it all out; I just mean that many quantum-level events have this kind of randomness to them. A given particle has a 50% chance of decaying or not in a certain span of time (its half-life), another particle, moving through a certain experimental apparatus, has a 50% chance of going thisaway and a 50% chance of going thataway, etc., etc. It’s so plausible, at some level, that I feel myself half believing it.

Second, as noted above, it actually explains why people in the fictional universe aren’t constantly inundated with hordes of time tourists. Who’d take this risk?

Third, this time travel physics has excellent dramatic possibilities: If you’re desperate, if you need to go back in time, you could just risk it. Just bite the bullet, push the button, and hope you go in the right direction.


Davis does this, and gets lucky: He gets back into the past. There are some great scenes in which he watches himself get drugged by Belle, etc. At any rate, he gets to solve all his problems and save the girl (and his cat – this is Heinlein after, all). The story is good – I’ve stripped off most of the dramatic turns and emotional hooks for brevity, but I recommend it as entertainment. And I’ve always loved what Heinlein did with the physics.

And there was one cool little moment that popped up in the comments at Logsdon’s site, linked to above:

Davis is talking with the physicist, Twitchell, who had a younger colleague who wanted to chance it. Twitchell recounts to Davis that he demurred at first, but the colleague was insistent, and eventually Twitchell gave in. An adventurous sort, the colleague wasn’t content to take a journey of a few hours; he wanted to be displaced several centuries. So Twitchell sent him on his merry way. Which direction did he go? There’s no way to know. Or is there?

The subject’s name was Leonard Vincent. As he recalls this story, Twitchell says to Davis, “I’ve sometimes thought… no, just a chance similarity in names.”

Davis narrates, “I didn’t ask what he meant by this because I suddenly saw the similarity, too, and my hair stood on end.”

And I just got goose bumps as I recalled this scene, even though I know it’s fictional!

If you don’t catch the reference, think about it, or check out the comments at Logsdon’s site.