Article: Randall Munroe (xkcd) on disappearing oceans

What If?
What If?

Have you ever wondered:

What would happen if all the bodies of water on Earth magically disappeared?

The answer – involving ships plummeting kilometres down to the ocean floor – is entertaining. Randall Munroe of explores this question as part of his What If? series. He has removed all the ships from the sea. He has discussed slowly draining the world’s oceans, and in a follow-up, dumping all that water on Mars. Now he drains the oceans in an instant:

The Titanic sank in about two miles of water. After it disappeared beneath the surface, the two halves of the ship took between 5 and 15 minutes to reach the bottom. Without the ocean there, it would have reached the bottom in about 30 seconds, striking it at airliner cruising speed.

As usual, it’s the stuff that happens afterwards that is the most interesting. Hang onto your seats.

Read the full What If? here.

xkcd: Fish

The Fermi Paradox is the seeming contradiction between the high estimated probability that extraterrestrial life exists, and the lack of evidence for any such life so far.


If you can’t see fish (analogous to the aliens), they’re probably camouflaged. Why would that be necessary? Perhaps a predator is doing the rounds? The most likely threat to civilisation on earth, apart from our good selves, would be another civilisation.

This is actually quite a terrifying comic.

See the original on the xkcd website. Want more explanation? Try here.

xkcd: 10 day forecast

10 day forecast
10 day forecast

An obsession with the weather – chiefly wind and speed and direction – pervades much of our time at home, as Tony plans dives and attempts to give the best possible experience to his customers within the time parameters they set for him. The different weather sites (,, WindGuru, WindFinder, Wavescape) seem to have periods of excellent accuracy, or different strong points. For example, is very good at predicting what time rain will arrive.

The long term forecast is something I check when we have something planned – like whale watching or cage diving – that requires decent conditions for it to go ahead. Unfortunately long term weather forecasts are usually highly unreliable. But it does give you something to look at while you count sleeps…

xkcd recently had something about a ten day forecast. The cartoon is here, or click on the image above.

xkcd: Increased risk

Increased risk
Increased risk

Let us bear this extremely pertinent fact in mind, with particular reference to the maps about sharks we looked at last week (part I, part II): Doubling (or tripling, or quadrupling – you get the idea) a one in a million chance – of meeting a shark, say – makes it two in a million, which is still very unlikely. Keep some perspective here.

xkcd: Seashell

A recent xkcd cartoon combines statistics (Bayes’ theorem) with an ocean theme, which makes me happy. Bayes’ theorem enables you to calculate conditional probabilities, which is the probabilty of something happening (or being true) given that something else has happened. You can also rearrange the formula to calculate straight probabilities if you know the conditional probabilities. It’s useful.

Conditional probability isn’t a difficult idea. For example, the probability that the next person you see will be female is different (probably higher) to the conditional probability that the next person you see will be female, given that you are standing at a urinal. The condition is that you’re in a men’s restroom.


P denotes probability, and the vertical lines denote conditional probability – read “given that”. The way to read the text in this cartoon is as follows: the probability that you are near the ocean, given that you’ve just picked up a seashell, is equal to the probability that you’ve just picked up a seashell given that you’re near the ocean, multiplied by the probability of being near the ocean, divided by the probability of picking up a seashell.

The author (Randall Munroe) of xkcd notes that the equation is roughly equal to number of times I’ve picked up a seashell at the ocean / number of times I’ve picked up a seashell, which is roughly 1, because one almost always picks up seashells at the beach and not elsewhere.

What the caption means is that if you picked up a seashell, you’re probably at the ocean (so you don’t need to hold it to your ear). The explain xkcd wiki may help. Anyway. Methinks I explain too much.

The comic can also be viewed on the xkcd website.