xkcd thread

Yeah. I tried to take @Civil_Guy’s suggestion to incrementalize that sentence further, but pretty quickly it wasn’t safe to post. So I abandoned it.

Groan.

The mouseover makes it worthwhile, though.

“Actually, my research shows that it only takes 0.9999… minutes to cross.”
“But that means we’ll never get there!”

Why doesn’t he get rid of some unnecessary constellations? Do we really need two Coronas? Especially considering the current state of world affairs.

Don’t really get this one. Is it a reference to a movie or commercial? I mean the interrupting part; I get why ‘timing’ is the secret.

The interruption is part of the joke. She doesn’t even wait for him to finish, i.e. waiting for the right time to tell the secret. I’ve heard jokes where interruption is part of the humor. It creates a surprise/shock reaction that can amp the humor for some.

Swap in “comedy” for “detecting gravitational waves using pulsars” and it’s an old, old joke.

You must not have a 6-year old.

Knock knock!
Who’s there?
Interrupting cow.
Interrupting c–
MOOOO!

The original is “Secret of comedy”. (Edit: as Wheelz already said)

Pulsars are variable stars that pulse at a precise interval. According to Wikipedia:
The periods of pulsars make them very useful tools for astronomers. Observations of a pulsar in a binary neutron star system were used to indirectly confirm the existence of gravitational radiation. The first extrasolar planets were discovered around a pulsar, PSR B1257+12. In 1983, certain types of pulsars exceeded atomic clocks in their accuracy in keeping time.[3]

So, basically the precise timings of pulsars can be used to detect gravity waves.

It’s more than that. Observations of the binary pulsar showed that it was losing energy at a rate that corresponded to what was predicted by gravitational waves, but the waves themselves were not directly detected. What Munroe is referring to here is pulsar timing arrays, which can directly detect gravitational waves. Basically, you look at one pulsar over here, and another one over there, in a completely different part of the sky, and use them as the test masses in an extremely large (hundreds or thousands of lightyears) gravitational wave detector. Or, more realistically, not just using two pulsars, but every pulsar you can find. By comparing the timing of pulses from all of them, you can (in principle) detect gravitational waves (from some other, much more distant source) passing through the space between the pulsars and us.

For a while, it was a real horserace to see whether pulsar timing or LIGO (and LIGO-like instruments) would be the first to detect gravitational waves. LIGO ended up winning that race a few years ago, and pulsar-timing arrays still haven’t caught up. But they’ll still probably be the second technique to succeed (other techniques further behind include resonance bars, and space-based detectors like LISA).

Personally, if I saw aliens on Earth, I’d be most worried about the War-of-the-Worlds Effect. Bacteria or other microbes (although not viruses) from either side could be hazardous to the other. But actually, the titletext is probably correct. If you see aliens on Earth, they’re most likely a hoax.

For context:

And a thread on the discovery: Potential detection of phosphine on Venus