Editing 2800: Down

{{comic
| number    = 2800
| date      = July 10, 2023
| title     = Down
| image     = down_2x.png
| imagesize = 611x290px
| noexpand  = true
| titletext = It's just that I get nervous about heights.
}}

==Explanation==
The direction that we call "down" is usually defined as the direction in which objects on Earth fall, which, for all intents and purposes, is the same as the direction that points toward the center of the Earth. This direction is therefore relative, as it depends on where you are located in relation to Earth's center, and is different for people in different locations. For example, from an outside viewpoint, the direction of "down" for people in {{w|Madrid}}, Spain is the opposite of the direction of "down" for people in {{w|Weber, New Zealand}}, as these two places are located at {{w|antipodes|antipodal points}} on Earth.

It is possible to redefine "down" by choosing a different point of reference, such as the center of a ''different'' planet, which is the situation shown in this comic. We see [[Megan]] seated at a desk, which would be perfectly normal if not for the fact that the scene is shown at a completely unnatural, almost upside-down angle. Megan explains to [[Cueball]] that the direction of "down" was redefined to be relative to {{w|Mars}} instead of Earth. Since Mars is located in space many millions of miles away, this means that "down" could potentially be in almost any direction.

Redefining down to be relative to Mars would be impractical for people on Earth,{{Citation needed}} as Mars is constantly moving with respect to Earth; this means that the direction of down will drift over time. Additionally, as Earth rotates once per day, the direction of down would also experience a 24-hour periodic wobble. It would be very difficult to keep track of this constantly-changing direction. Setting down relative to Earth's center avoids these problems (at least for beings on Earth!), as the Earth's center is static in relation to the motion and rotation of Earth.

Megan does not explain who exactly redefined down, or why they have the authority to do so, but it is most likely some scientific body such as the {{w|International Astronomical Union}} or the {{w|General Conference on Weights and Measures}}, which have the power to make such decisions - for example, the IAU defined planet and {{w|dwarf planet}} in 2006, and the GCWM redefined the {{w|kilogram}} in 2018. In reality, in addition to there being no governing body which determines the direction of down, such definitions are made only when there is compelling reason to, and they work hard to minimize the changes. (For example, the redefinition of the kilogram was done in order to ''prevent'' the mass of the kilogram from changing in the future by attaching it to physical constants.) Nonetheless, in the world shown in this comic, redefining 'down' appears to happen frequently enough for Cueball to be frustrated but not fazed by it.

It should also be noted that redefining down does not automatically alter the direction of gravity, which will still act in the same direction it did before. Therefore, it is unclear how Megan or Cueball are even aware of the change in definition, unless they are somehow {{tvtropes|MediumAwareness|aware of the comic they are in}} and "know" that they are oriented at a strange angle.

Cueball mentions that the redefinition of down is a side effect of redefining the origin of their coordinate system. A {{w|coordinate system}} is a way of representing locations in space using a set of numbers, where each number (called a coordinate) measures a distance travelled in one of the spatial dimensions. In order for these numbers to be meaningful, it is always necessary to define a single point as the origin, where all coordinates have the value 0. Locations can then be measured relative to the origin.

For example, a commonly-used coordinate system for Earth is the {{w|Earth-centered, Earth-fixed coordinate system}}, which defines the origin to be Earth's center of mass, and uses three pairs of points on the Earth's surface to define the directions of the three spatial dimensions; this allows any point relative to Earth to be specified as a triplet of three coordinates. Presumably, the coordinate system now used in the comic is a "Mars-centered, Mars-fixed" coordinate system, which would be good for things like launching satellites from Mars, but otherwise not very useful for most Earthly situations.

In the title text, Cueball states that he gets nervous about heights. Height is the distance between two points at different elevations, and elevation depends on which way "down" is - therefore, redefining down also redefines the concept of height. Since down now points toward Mars, and Mars is millions of miles away (about 34,000,000 mi or 55,000,000 km at closest approach), this means that Cueball - and indeed, everyone on Earth - is now standing at a height of about 34 million miles above Mars. While fear of heights is a common cause of anxiety, it doesn't really make sense for Cueball to be nervous in this instance - usually, when people are afraid of heights, it's because they are afraid of falling. However, gravity still points toward the center of the Earth, so Cueball is in no danger of falling to Mars. The joke is that Cueball is scared solely due to the redefinition of the situation - where previously he was standing on solid ground, now he is "perilously" clinging to the underside of a planet with a 34-million mile drop beneath him.

The only advantage of using Mars as down, is that everyone on Earth agrees on the direction of down, since Mars is so far from Earth that even those on either side of Earth orthogonal to the direction towards Mars, would still almost agree on the down direction.

In the recent game comic [[2765: Escape Speed]], the planet outside of the Crystal Sphere, based on the [[Click and Drag]] comic, doesn't have it's own gravity. So the space ship is pulled towards the Crystal Sphere no matter what side of this planet the space ship is located. This makes navigating difficult. Only the fact that landing on the surface (and sticking to it) is possible, makes it possible to explore the planet properly. 

The comic might be a reference to the novel ''Ender's Game'' by Orson Scott Card, in which the protagonist, Ender, notes that the directions "up" and "down" are arbitrary in space, and that it can be helpful to think of "down" as towards the enemy's base.  This aspect of ''Ender's Game'' was previously referenced in [[241: Battle Room]]

==Transcript==

:: [Megan is seated at a desk, in front of a laptop. The scene is rotated by 150° clockwise, so she appears to be upside down and angled.]

:: [Cueball enters the scene from the right side, behind Megan. He has three question marks below his head, oriented upright in frame.]

:: Megan: They announced that "down" is relative to Mars today.
:: Cueball: Ugh, I hate when they make another planet the coordinate system origin.

{{comic discussion}}

[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Physics]]
[[Category:Astronomy]]