1606: Five-Day Forecast

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Five-Day Forecast

Title text: You know what they say--if you don't like the weather here in the Solar System, just wait five billion years.

Explanation

Weather forecasting is an extremely difficult task, even if it is only for five days. In numerical models, extremely small errors in initial values double roughly every five days for variables such as temperature and wind velocity. So most meteorologists provide us with only a five-day forecast.

In this comic Randall takes this to the extreme by first showing a Five-Day Forecast and then progressing to five-month, year, million, billion and finally trillion-year forecasts, leading to weather patterns that we don't regularly see.

Since the first weather symbol is the same in all six rows, we can assume it indicates the weather today and not tomorrow, in a trillion years, etc. It is only in the second panel of each row that time has passed per the row's label. Consequently, the last column gives the predictions for four days, four months, ..., four trillion years from today.

When moving past the five-day prediction, the forecast is just a qualified guess based on the time of year. In a month it is Christmas as shown in the second panel of the second row. Then it is January and February so snow is likely, but certainly not something that happens on all days of a winter month.

Looking at the five-year forecast, guesses are made as to what the weather will be like at the same time of year. For these first three predictions the weather symbols are all of the same three types: Sun, clouds and some kind of precipitation, rain or snow, with the temperature ranging from 21 to 44 °F (-6.1 to 6.6 °C) - winter temperatures.

Then we go into the far future, jumping a million years from panel to panel. But still the weather symbols stay the same. In 3 million years, however, aliens (or advanced humans) attack with energy beams from flying saucers. They are gone a million years later. The temperature range remains the same across the panels except that it rises to 52 °F (11 °C), a possible reference to global warming, in one panel, and while the attack is going on it rises to 275 °F (135 °C).

Once we get to the billion-year mark it actually becomes more meaningful to try to predict the "weather", because now we reach the times when the Sun begins to change. Although the Sun will continue to burn hydrogen for about 5 billion years yet (while in its main sequence), it will grow in diameter as it begins to exhaust its supply of fuel. The core will contract to increase the temperature, and the outer layer will then compensate by expanding slightly. This is what is indicated in panels two and three, where the color of the Sun changes towards red as the surface becomes cooler as it expands away from the center of the Sun. The temperature will rise on Earth as indicated in the panels (105 °F = 40.5 °C and 371 °F = 188 °C). The temperature will get hot enough in about a billion years that the Earth's oceans will boil away.

Once it no longer has enough hydrogen, the Sun will expand into a red giant. This should not happen until around five billion years from now, but in the forecast it is indicated to happen in only three. Maybe this is Randall taking liberties to show what happens during this phase, which would not fit into a four-billion-year forecast. Alternatively it just indicates how uncertain these kinds of forecasts are, or a statement that we may not know for certain that it will take five not three billion years.

In any case, the fourth panel shows the temperature at Earth's position inside the red giant Sun. The color of the panel indicates that we are inside the Sun. The temperature is 71,488,106 degrees Fahrenheit (39,715,597 degrees Celsius). The current temperature of the center of the Sun is "only" 27 million degrees Fahrenheit (15 million degrees Celsius), and although that may rise by a factor of ten during helium fusion, that will only be at the very core and not out in the solar atmosphere reaching out to Earth. Here the temperature would only be of the order of thousands of degrees Fahrenheit, since the Sun's outer temperature decreases as it increases its diameter. So this panel's temperature also makes little sense. It may involve some ambiguities regarding what the forecast means; the edge of the red giant Sun is predicted to be somewhere near the current orbit of Earth, but the position of the Earth could change. The most likely prediction at the moment is for Earth to move outward, but if the planet is engulfed by the Sun, it would spiral inward, and at some point fall apart. So in some sense "here" for the forecast could become a position deep inside the Sun, where core temperatures could reach 100 million Kelvin. The temperatures shown are unreasonably precise; they probably should have only two or at most three significant figures.

The red giant phase lasts only half a million years, so a billion years after the Sun has been a red giant its outer atmosphere will definitely have disappeared, leaving only a dim, cool white dwarf to cool down. Given Randall's version of this time schedule, then it will have had about a billion years to cool down, but would still likely be the brightest object in the sky as seen from where the Earth once was. It is not shown in the last panel, where we just see other stars of the Galaxy. The temperature is down to that of the background radiation. Today this radiation has a temperature of 2.72548 kelvin = -270.4245 °C = -454.7641 °F. That is a few degrees F colder than what is shown in the comic, which states the temperature is -452 °F = 4.26 kelvin. This higher temperature may have been chosen to reflect that even the light from other stars would increase the actual temperature.

In the last panel with trillions of years, we jump right past the Sun's red giant phase to a panel looking much like the one after five billion years with only other stars. Over the next three trillion years the stars become fewer and fewer and dimmer and dimmer as they run out of fuel and fewer new stars form. After four trillion years the background temperature decreases one degree to -453 °F as the universe keeps expanding and the wavelength of the radiation does the same, thus decreasing its temperature.

The title text is a play on comments referring to fast-changing weather on a more ordinary human timescale, such as Mark Twain's quip, "If you don't like the weather in New England now, just wait a few minutes."

A ten-day forecast was used in 1245: 10-Day Forecast. In 1379: 4.5 Degrees, Randall looked at the weather over long periods of time as well. in 1643: Degrees he addressed Celsius vs. Fahrenheit for measuring temperature.

Image using Celsius

A different user-made version for the picture using Celsius instead of Fahrenheit can be found here: Five day forecast in Celsius.

Transcript

[A grid with six rows of five columns, where each row is labeled to the left. For each of the 30 squares a temperature is given in Fahrenheit at the top left. The rest of the square represents the weather as in a weather forecast (or some other relevant items for the comic), mainly in bright colors. Below are the six labels given above each of their five weather symbols with temperature given below these symbols description.]

Your 5-day forecast

[A bright yellow sun.]

38°F

[A grey cloud.]

41°F

[A grey cloud with six lines of blue raindrops below.]

36°F

[A grey cloud in front of a yellow sun.]

40°F

[A bright yellow sun.]

44°F

Your 5-month forecast

[A bright yellow sun.]

38°F

[A green Christmas tree with red presents beneath it.]

29°F

[A grey cloud with four snowflakes below.]

21°F

[A grey cloud with four snowflakes below.]

24°F

[A grey cloud.]

35°F

Your 5-year forecast

[A bright yellow sun.]

38°F

[A grey cloud.]

25°F

[A bright yellow sun.]

36°F

[A grey cloud with six lines of blue raindrops below.]

37°F

[A bright yellow sun.]

41°F

Your 5-million-year forecast

[A bright yellow sun.]

38°F

[A bright yellow sun.]

52°F

[A grey cloud.]

40°F

[Two red flying saucers (with bright domes) are shooting energy beams downwards. One of the beams seems to impact with something at the bottom of the panel, which then explodes. Two plumes of smoke rises up from below, drifting to the right.]

275°F

[A grey cloud in front of a yellow sun.]

40°F

Your 5-billion-year forecast

[A bright yellow sun.]

38°F

[A larger orange sun.]

105°F

[A very large red sun.]

371°F

[A pale yellow panel with no drawing.]

71,488,106°F

[A night sky with many bright stars.]

-452°F

Your 5-trillion-year forecast

[A bright yellow sun.]

38°F

[A night sky with many bright stars.]

-452°F

[A night sky with many stars.]

-452°F

[A night sky with fewer not so bright stars.]

-452°F

[A night sky with few dim stars.]

-453°F

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Discussion

As far as I can figure out, -452 F is something like 4 K, which seems a bit too warm (above OTL microwave background). It probably should be -456 in the next-to-last row and -458 in the last row (-459 for the last column). --141.101.81.76 12:58, 20 November 2015 (UTC)

Inside a galaxy, it presumably is a bit warmer than CMB, since there are stars around to heat the interstellar medium a little. --Aaron of Mpls (talk) 05:40, 22 November 2015 (UTC)

If Randall is going to use Farenheit why don't we stick with Rankine, thus -452 F works out at about 8 R? (Saves all the messing about with multiplication and division) 162.158.34.147 13:15, 23 November 2015 (UTC)

Thanks for the conversions to degrees C as being a 58 year old Brit I have never understood degrees F (I know what they are just I have no idea whether 60F is cold, cool or comfortable). I have always used 5, 10 and 21, Winter, Spring and Summer sun - well works for Middle Brittan) RIIW - Ponder it (talk) 19:09, 20 November 2015 (UTC)

FYI 60 degrees F outside is quite pleasant, a little cool, but inside your feet get cold. 15.5 degrees C NotLock (talk) 09:12, 22 November 2015 (UTC)

Yes thank you for the conversions, _most_ readers of this comic use metric units: http://daretorant.com/wp-content/uploads/2010/06/metric-system.jpg Martin (talk) 21:52, 22 November 2015 (UTC)

As a younger Brit (56) I grew up with Farenheit, I'm not sure where in the UK our 58-year old grew up, but I don't remember a concerted effort to use SI units until the mid seventies. For me it's the other way 'round: 60F sort of OK as long as it isn't windy, 70F quite warm, 80F Phew! What a scorcher! All the centigrade equivalents are just too small! :) 162.158.34.147 13:15, 23 November 2015 (UTC)

Perhaps the original Brit is only 58F, and was born c. 2000.108.162.238.87 21:09, 1 December 2015 (UTC)

There will be ambient starlight in addition to the 2.7K background which should raise the temperature slightly. However, the 2.7K background will also redshift to a lower temperature as time goes on: T propto 1/a where a is the scale factor of the Universe. Would be a good assignment for a cosmology class. 173.245.54.48 13:07, 20 November 2015 (UTC)

Aha, what will last longer than stars etc is the silly Fahrenheits. 162.158.91.165 17:49, 20 November 2015 (UTC)

There are five columns. Either the first column is "today" and one should not speak of predictions after five (m/b/trillion) years (as is currently the case a couple of times), or the first column is "tomorrow (etc.)" and then the prediction of "A bright yellow sun; 38°F" for one trillion years would be very strange. Jkrstrt (talk) 18:39, 20 November 2015 (UTC)

Randall lives in a cold climate! 188.114.97.127 21:37, 20 November 2015 (UTC)

If the "red giant" temperature measures the sun's core, how do you explain the last panels showing decidedly non-white-dwarf temperatures? --199.27.130.234 03:48, 21 November 2015 (UTC)

Regarding the 5-year-predicion: It seems to me that the temperature is in average rising a bit across the year, maybe a reference to the slow process of global warming? This would not be the first time, there are even whole comics just about global warming, especially about the noticeable speed and the "in average"-importance (e.g. 1379, 1321) 162.158.92.118 (talk) (please sign your comments with ~~~~)

I don't believe so. Five years is probably too short a period for discussing global warming. Limit it to a single place and even more so. Limit it to a sample of one day per year, and I believe you can't bother looking at the p-values. --Ahyangyi (talk) 15:56, 29 March 2016 (UTC)

Image with °C

I hope someone will find my low-effort edited version useful: http://www.explainxkcd.com/wiki/index.php/File:five_day_forecast_Celsius.png --Asdf (talk) 18:15, 26 June 2017 (UTC)

Nice work. It's mentioned above the explanation section. I'm hoping the values are correct. ;-) --Dgbrt (talk) 18:39, 26 June 2017 (UTC)

Thanks, I thought it'd be forgotten. I rounded the last value down from -269.44... to -270 degrees C to keep the joke though.

Edit: Of course someone had thought of this before. See this Reddit thread to see a better image and conversion to kelvins. --Asdf (talk) 20:56, 26 June 2017 (UTC)

I’m thinking that maybe the flying saucers arrived to help us evacuate the planet (using tractor beams), before it was too late. Brenda (talk) 12:17, 21 May 2019 (UTC)