1642: Gravitational Waves

Explain xkcd: It's 'cause you're dumb.
(Redirected from Gravitational Waves)
Jump to: navigation, search
Gravitational Waves
"That last LinkedIn request set a new record for the most energetic physical event ever observed. Maybe we should respond." "Nah."
Title text: "That last LinkedIn request set a new record for the most energetic physical event ever observed. Maybe we should respond." "Nah."


Megan, Cueball, and Ponytail are observing the results from a gravitational wave detector (see details below). This comic came out on the day that the first direct observation of gravitational waves was publicly announced on 2016-02-11. The actual event was recorded five months before on 2015-09-14, but it was not reported publicly before they were sure it was a real signal. It seems that Randall knew in advance about this announcement because this comic was published on a Thursday, not following the normal publish schedule, to coincide with the announcement, and there were no other comics released Friday that week. (The altered schedule could be viewed as a meta-reference to the warping of spacetime.) That scientists knew there might be an announcement on the way, and more details for the interested can be seen in these two videos from Space Time: Have Gravitational Waves Been Discovered?!? and LIGO's First Detection of Gravitational Waves! (See also their follow up The Future of Gravitational Waves).

This is the second time within a month that a new astronomical announcement (of something discovered months before the actual announcement) has resulted in a related comic. The first being 1633: Possible Undiscovered Planets.

From the patterns in the gravitational waves detected by this instrument, it might be possible to guess the nature of the event (e.g. two bodies with dissimilar masses circling a fixed point, two bodies with equal mass circling each other, collision of two massive bodies, etc.). It might also be possible to triangulate the location of the event. Based on these two facts (the location and nature of the event) we might be able to determine which astronomical bodies caused this event (and the status of those bodies afterwards). Thus, it provides an additional medium to observe the universe in addition to telescopes observing all kinds of electromagnetic radiation. This new medium might enable us to observe properties that we couldn't observe with the rest of our observation instruments.

However, the scientists in this comic appear to be receiving more than the expected signals from black hole collisions, they also receive gravitational spam messages, such as invitations from Linkedin, a mortgage offer, and an announcement of a social meet-up, rather than observing astronomical events (see table below).

There is also a joke on the social meet-up's use of the word local group because the 'Local Group' is also the technical name for the group of galaxies containing the Milky Way.

It is not clear if these so-called "events" are causing gravitational waves to be generated or if something, perhaps an alien civilization, is encoding spam messages in gravitational waves. It is plausible that aliens are using gravity waves to encode their messages, as we do something similar with electromagnetic waves to encode and send our messages. However, it would take an extremely advanced civilization to achieve gravity wave encoding. It requires the controlling of orbits and oscillations of super-massive bodies like the Sun, or more likely bodies ten times more massive than it. For example, the first event detected, both in this comic and in real life, was a merger of two black holes of roughly 30 solar masses each.

The title text makes the speculation, that something is sending spam encoded in gravity waves, seem more plausible, as it follows up with a joke that the message senders have gone to such a length that they caused the most energetic event recorded ever (perhaps on the scale of a few supernovae or black hole collisions). One of the scientists is so impressed with this effort that he suggests that they actually post a reply, but one of the other person declines with a "Nah"! (As you should always do with spam, else you will just encourage the sender by making it clear that there actually is a receiver on this address.) Randall may have been referring to the fact that the detected event had a power output equal to 50 times that of the entire visible universe.

In 1365: Inflation gravitational waves are also mentioned.

Gravitational waves[edit]

A gravitational wave detector is a device used to measure gravitational waves, small distortions of spacetime that were first predicted by Albert Einstein in 1916. Gravitational waves are ripples in the spacetime fabric itself.

In layman terms, a gravitational wave is like moving a stone through water while partly submerged. It will cause waves on the surface of the water as it moves through it. These waves will spread away from the center of disturbance and as they move, they will cause the water molecules to oscillate around their mean positions. Similar waves are created in the space-time fabric when two celestial bodies interact with each other. If you concentrate on an area of the fabric far away from the point of disturbance, it can be observed that if the wave causes compression in one direction, it'll cause expansion of the fabric in the other. See this page for nice animations.

Note that anything with a mass will cause a gravitational wave. Just as waves created by small stones are tiny in comparison to waves created by huge rocks in water, the waves from humans moving around will be tiny compared to the waves created by celestial bodies. Also, the bigger the body, the stronger the wave and the farther away it can be detected. That is why we can only detect gravity waves from heavy bodies like black holes or neutron stars but not from us moving around further than around 10m from the test masses. (the LIGO Hanford observatory has also had problems with tumbleweeds hitting the building and had to build a fence).

Now, let's consider spacetime fabric as a thin rubber sheet. If you mark any two points on this sheet and stretch or compress it along the axis joining those two points, the relative positions of these points with respect to their neighboring points do not change, but the distance between them changes.

LIGO (Laser Interferometer Gravitational-Wave Observatory) is a large-scale physics experiment designed to detect this compression/expansion, and it was LIGO who discovered the signal that caused this comic. (For a very detailed description of what the team at LIGO did and the history behind see this 90 minutes feature Gravitational Waves: A New Era of Astronomy Begins from the 2016 World Science Festival).

Two facts need to be remembered to easily understand the experiment. First, the speed of light (c) is constant and the speed of an object is the distance moved divided by the time taken to travel that far. Second, gravitational waves cause opposite effects (compression and expansion) in directions perpendicular to each other. At LIGO, an experiment is set up where two perpendicular long tunnels are constructed with apparatus to emit and detect laser beams. The beam from a laser is split into these two tunnels. After going through the tunnel and back again a few times the beams are brought back together. The lengths of the tunnels are set up in such a way that, in the absence of gravity waves, destructive interference between the two combined beams causes them to cancel one another out, resulting in the detector observing zero light intensity. When the gravitational wave passes through earth, one of the tunnel is expected to expand while the other is expected to compress. Due to the difference in lengths, the destructive interference is incomplete and the detectors will be able to detect the presence of light. This observation can be concluded as "detection of the gravitational wave passing through".

Explanation of observed events[edit]

Event Explanation
Black hole merger in Carina (30 M, 30 M)

Possibly legitimate result from the gravitational wave detector. M means 1 Solar Mass (1.98892×1030 kg). So the statement means that two black holes, each one 30 times more massive than our Sun were observed merging in the Carina constellation. This observation is similar to the one actually reported in the announcement on the day of this comic, were the two black holes had masses of 36 and 29 solar masses (with an uncertainty that meant they could have had masses as close as 32 and 30 solar masses vs the 30+30 in this event). Also the location of the event matches with Carina. Although at present time it is not possible to pinpoint the location of the event (that will need more detectors spread out across Earth) they still manage to find out that it most likely originated in the Southern Celestial Hemisphere, which is also where the Carina constellation is located.

Zorlax the Mighty would like to connect on Linkedin

A typical LinkedIn request. As this may be a message encoded in gravitational waves, it either means that LinkedIn has now grown outside the Earth, or that the Zorlax person would like to contact Earth. Zorlax is likely a reference to a kid's television gameshow, based on time travel, Zorlax and the Time Travellers. The first sentence in the movie is: Four billions of years ago in the Earths core, destined to be the master of time he is the Mighty Zorlax. It is likely someone with the power over time would be able to create gravitational waves at his own leisure.

Black hole merger in Orion (20 M, 50 M)

Again, a possibly legitimate observation from the gravitational wave detector. It detected a black hole merger of two bodies in the Orion constellation. One of them is 20 times more massive than Sun, the other is 50 times more massive than the Sun. As Orion is located at the celestial equator and since the masses are far from the one announced on the day of this comic, this would then represent a possible 2nd event to be measured later.

Mortgage offer from Triangulum Galaxy

Triangulum Galaxy, also known as Pinwheel Galaxy, is a spiral galaxy approximately 3 million light-years from Earth. It is the third largest galaxy in the Local Group after the Andromeda Galaxy and the Milky Way, these three being the only spiral galaxies in the group. This is presumably an offer to extend a loan, with a house on Earth serving as collateral. However, unless we develop wormholes or faster-than-light travel technologies, it will be difficult to submit an application, even if the offer is legitimate.

Zorlax the Mighty would like to connect on Linkedin

Same person who sent us LinkedIn invite moments ago. This repeated request may imply that Zorlax is desperate, or may be a jab at LinkedIn's persistence in spamming users with unaccepted connections to view and/or accept them. According to the title text, this was the most energetic physical event ever observed; it may be that Zorlax is demonstrating his capabilities in the hopes that the request would be accepted.

Meet lonely singles in the local group tonight!

The space advertisers are using space-GeoIP technology on a galactic scale to send spam. A Local Group is the technical term for the group of nearby galaxies that also includes the Milky Way, our own galaxy. There are more than 54 galaxies and few other celestial objects in our local group. This Local Group along with several others form the Virgo Supercluster. It would seem that the advertiser is targeting ads to everyone in the Virgo Supercluster. However, finding "lonely singles" in the 54 galaxies within our local group might be easier said than done for humans here on Earth. Another joke is that human race has been trying to find not just "lonely singles" but any lifeforms beyond Earth for the past few decades and hasn't been able to find them successfully. It seems that gravitational wave detector in the cartoon helped with this mission as well. This kind of spam was previously featured in 713: GeoIP.


[Cueball, with arms up, is standing behind Megan who has her hands at her mouth, and who in turn is standing behind Ponytail, who is sitting in front of a large computer console with a screen, a keyboard, and several items on the side (presumably lights and labels). Three wires lead away from the console out of the image to the right.]
Megan: The gravitational wave detector works! For the first time, we can listen in on the signals carried by ripples in the fabric of space itself!
[Larger panel with the same setting in the middle, but both Cueball and Megan have taken their arms down. More of the wires from the console can be seen to the right. The computer lists six events:]
Computer: Event: Black hole merger in Carina (30 M, 30 M)
Computer: Event: Zorlax the Mighty would like to connect on Linkedin
Computer: Event: Black hole merger in Orion (20 M, 50 M)
Computer: Event: Mortgage offer from Triangulum Galaxy
Computer: Event: Zorlax the Mighty would like to connect on Linkedin
Computer: Event: Meet lonely singles in the local group tonight!

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


"Local group" refers to https://en.wikipedia.org/wiki/Local_Group. Lonely singles (black holes?) meeting on a galactic scale would produce another gravitational event. 21:39, 11 February 2016 (UTC) Christoph Berg

Should we add a Trivia section regarding the fact that this comic was posted outside the normal M-W-F schedule? Edo (talk) 23:03, 11 February 2016 (UTC)

Should there be some kind of mention of the possibility (or lack thereof) of artificial gravity waves being used for long-distance communicaiton? --Joshupetersen (talk) 23:41, 11 February 2016 (UTC)

I'm not sure everyone knows what the solar mass symbol looks like. Thaledison (talk) 23:51, 11 February 2016 (UTC)

I think the explanation needs a bit more on the analogy that humans rely heavily on electromagnetic waves for communication. It is reasonable to expect aliens to use gravitational waves for the same as the theoretical basis for encoding messages would likely not need to be change. 08:29, 12 February 2016 (UTC)

Please go ahead and edit it, I'm done for now. I've added lots of stuff. This is the first comic I've tried explaining in full, and it has become quite big. ;-) So far I was only doing small edits here and there... 09:16, 12 February 2016 (UTC)
EDIT - I added a sentence about it. Please do any further edits if you like... 09:24, 12 February 2016 (UTC)
I think this has something to do with |Google Wave or am I overthinking it? 12:11, 12 February 2016 (UTC)

Odd for a massive-object-related comic to not contain a your-mom-joke reference. 12:09, 12 February 2016 (UTC)

"Black hole merger in Carina (30 M☉, 30 M☉)" refers to the public announcement of the first detection ever made of gravity waves from the LIGO-VIRGO experiment. The announcement has been publicly done thursday 11 February 2016, the same day the drawing has been done. This is not a "Possibly legitimate result", but a scientifically proved legitimate result. The drawing has been done in honor to that major scientific first ever observation (which will probably lead to a Nobel Price). -- 15:04, 12 February 2016 (UTC)

I think that the word "merger" is a pun. It is not normally used to describe black hole collisions, but is common in spam messages about stock tips. Not being a native English speaker, I wouldn't attest this, but someone who is might confirm... Mumiemonstret (talk) 11:26, 14 September 2016 (UTC)

"Zorlax is a kid's television gameshow, based on time travel", and "Formed billions of years ago in the earths core, cursed to be but a floating head, gifted with a knowledge of the ages and destined to be the master of time. He is the mighty... ZORLAX!" See here and here. Maybe someone knows this kid's television gameshow. --Dgbrt (talk) 19:21, 12 February 2016 (UTC)

I did not , but I found the reference by googling without spotting your post. It has been included in the explanation in the table. --Kynde (talk) 20:15, 22 February 2016 (UTC)

"One of the receivers is quite impressed with this and suggests that they have to reply to the spam just because the sender has made such an effort to send the message." This line: I actually interpreted the title text as worry rather than being impressed. If a cosmic being is moving around celestial bodies just to make a LinkedIn request and is making increasingly-intense messages, it might be best for the safety of whatever to prevent it from escalating any further. Am I the only one who understood it this way? Jeudi Violist (talk) 19:45, 12 February 2016 (UTC)

Just to be complete: The spam messages could also come from a prankster messing with the computer or some equipment between the experiment and the computer. Of course this is less (if at all) funny than the thought of encoding messages in gravitational waves. (talk) (please sign your comments with ~~~~)

De Speld (dutch "news" site similar to The Onion) reports the gravity waves are the result of natural gas production in Groningen. 14:41, 13 February 2016 (UTC)

I have a somewhat different take on this comic. The "Explanation of observed events" section seems to imply that these messages are directed towards earth. My interpretation is that the team has tapped into some sort of intergalactic internet, where stars are communicating with each other (and, perhaps, looking for other stars to mate with) Sysin (talk) 17:20, 13 February 2016 (UTC)

The event log is presumably a reference to some kind of computer event log, perhaps for network events. I'd assume it's modeled on some obscure Linux thing. I actually came here hoping for an explanation of what type of event log Randall is spoofing. 20:27, 13 February 2016 (UTC)


The Nature article on the discovery mentions that there was a number of "injections" of fake signals in LIGO to test whether the scientists can tell apart real and fake signals. The original signal now considered a confirmation of gravitational waves was first thought to be an injection. This comic might be showing such an experiment with a mixture of real and fake signals.

-- 14:22, 14 February 2016 (UTC)

Is it possible that the "most energetic event is a pun"? As in, "My kid is full of energy," or "That was an energetic party." Mikemk (talk) 08:24, 15 February 2016 (UTC)