Rainboom Research Review · 6:55pm Feb 6th, 2021
Let’s take a look back at something from the early days of FiM.
Discussions about the ‘physics’ of the sonic rainboom on internet forums was one of the things that drew me into the fandom in 2011-12, back in the days when no one paid much attention to politics and instead we had heated online arguments about different interpretations of cartoon physics. I didn’t write my own blog post about this at the time. There were so many attempts at this, I wanted to do something a bit different, so I wrote my story Rainbooms and Rationality instead.
We kick off with the YouTube video: Physical Impossibilities in My Little Pony: Friendship is Magic, which went viral in 2011, was picked up by mainstream media, and clocked up over 1.5 million views. The presenter analyses the rainboom clip, using the angle of the Mach cone to calculate Rainbow Dash’s velocity and show that reaching this would require a blackout-inducing 11.1g acceleration. In conclusion, the clip is rated “XP for dangerous acceleration, flying ponies, and breaking the light spectrum.”
This calculation was taken further in The Physics Behind the Sonic Rainboom, which points out that the acceleration leading up to the rainboom is nothing compared to the subsequent force which Rainbow Dash must undergo after saving Rarity in order to avoid hitting the ground. This requires a more extreme 1670g. Rainbow Dash – Physics is Magic did the calculation with different assumptions, taking the initial speed as hypersonic rather than sonic, and arrived at a result over an order of magnitude higher: 17,739g. While there may be disagreement about the numbers, this does not change the basic conclusion that Rainbow Dash is awesome.
A different perspective was offered by Physics from a Non-Brony: The Sonic Rainboom unraveled, which, after taking several paragraphs to set out why everyone else is wrong with key points highlighted in bold, makes the case the Rainbow Dash was actually moving at a sub-sonic speed by comparing her motion to the falling Rarity with reasonable assumptions about the terminal velocity of a falling pony. The author points out multiple times that they are not a brony.
While the calculations printed on pictures of ponies and rainbows were 20% cooler, the more interesting discussions were about the science and speculation about what could produce this violation of the light spectrum. I love it when anyone suggests she is breaking light speed, as it gives me the chance to talk about Cherenkov light and particle detectors. A more down-to-earth idea is a vapour cone, a cloud of water droplets that can condense in the path of a super-fast flying object, and could in the right circumstances reflect a rainbow spectrum, although not matching the rainboom very well.
While there has been so much attention paid to the rainboom itself, the details of the rainboom failure mode shown in Rainbow Dash’s initial training run have been largely ignored. Although this is perhaps a more physics defying feat than the rainboom itself.
Interesting. Even though I don't know enough about the subject to make an accurate theory, the vapour cone is the most likely option. If we look at Dashie in the seconds before the rainboom, a cone of what appears to be cloud forms in front of her. Still, I think we need to have a look at how the rainbooms fail like that and how the cone is able to make a pony spring backwards.
Just another reason I love this fandom, I don't ever remember having surprisingly deep discussions about topics like theology, physics, or history in other fandoms I've participated in.
It's a pity that there isn't a way to save favorite blog posts like there is for stories.
"Elasticity of the sound barrier" is definitely the kind of unexpectedly relevant terminology that makes Friendship is Magic such a delight to analyze.
My personal take on the rainbow part is something analogous to Cherenkov radiation. If we assume that magic propagates in a similar manner to light, but at much lower speed, it may be that a magical entity exceeding that speed creates a "thaumic shockwave."
As for the failure mode, maybe it has something to do with how flight magic, the compressed air in front, and the corresponding concentration of magic interact. Perhaps as Dash approaches the critical velocity, her flight magic is focused in front to shield her from the transonic effects, and the magic-saturated air becomes more and more "solid" in a similar manner to cloud structures. If she gets the magic focused just right, she is able to punch through this obstruction and continue accelerating; if her focus fails, she decelerates rapidly, and the compressed magic-air colloid rebounds, launching her away.
But that's just a theory. A MAGIC THEORY. Thanks for reading!
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Of course the speed of sound is connected to the elastic properties of a material. The reason why sound propagates is because when air is driven forwards it creates a pressure difference that pushes it back. But the idea that it could create a sufficient force to make a pony spring backwards is as crazy as ponies walking on clouds.
Yes.
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I feel like you might be a bit biased here. Just a pinch.
I agree with Eroraf86's theory.
I also watched RD get yeeted (is that the right term?) backwards more times than I probably should have
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Ah, right, that topic. Seeing some of the rainboom speculation online was what got me to finally take a closer look at those ponies I'd been increasingly seeing around the internet, all those years ago, as I recall. :)
Personally, I think that, if it's not just an even more different property of the universe, there's probably some interaction between the flight magic Rainbow Dash is using and the speed of sound in the medium she's moving through. The Rainboom State clearly appears to not just be flying faster and with more glow, given even conservative estimates of the accelerations needed on those turns, but a qualitatively (or quantitatively to the point of qualitatively, in the sense that both ice and steam could be described as H2O with different values for some parameters) different way of interacting with the world. This in turn implies a potentially interesting relationship between magic, and possibly just pegasus or equivalent magic, and the speed of sound transmission in the medium.
(Again, assuming an Equestria with physics sufficiently close to ours that that even applies -- but both ways there can be interesting, I think.)
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In other words, Dashie is awesome
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I see what Rainbow Dash’s entire problem was in recreating the rainboom! First, look at the second, animated image of a rainboom fizzle, and note that she has only one arm outstretched with the other folded under her. Then look at the first image sequence of a successful rainboom and note that she has both arms outstretched!
The sonothaumic barrier cannot be simply punched through as it reflects any thaumic field directed at it back at the source with strength proportional to the velocity of the oncoming thaumic field. Instead, interference is the name of the game. I hypothesize that Rainbow Dash is the rare pegasus that is capable of strong yet fine-grained manipulation of her thaumic field. By putting two hooves before her instead of just one, Rainbow Dash is able to use her thaumic field to set up an interference pattern (unconsciously, at first) in the sonothaumic barrier just ahead of her, forcing it to cancel itself out and creating a breach that she can then exploit for greater speed with accompanying optical, sonic, and (presumably) thaumic shock waves.
Or so I’ve heard.
I am open to the theory that all pegasus ponies are part-jet-fighter. It'd explain the sounds they make while zooming around.
Worth adding a couple of things to this discussion. Firstly, the biological factor: the fastest flying animals known are Peregrine falcons, which according to Wikipedia can achieve a maximum flight speed of close to 400 km/h. And they can only do that in a stoop or dive, using highly specialized wing and feather design. To achieve a conventional sonic boom, a flying animal would have to travel at the speed of sound, or 1,234.8 km/h. Frankly, sticking wings onto a basic pony body plan won't streamline you anywhere near enough. Conclusion: Magic.
Secondly, the prominence of a rainbow theme generally. Rainbow Dash creates a sonic rainboom that ends up triggering or catalysing the cutie mark acquisitions of six ponies who go on to wield the Elements of Harmony, which uses predominantly rainbow-based spells, which have also been used before (when Celestia banished Luna, the spell that created the Mare in the Moon also generated a rainbow shockwave on impact). And when Rainbow created the second rainboom, she was doing so to save a friend. Conclusion: Friendship.
Ergo, sonic rainbooms are friendship magic.
You know, one thing that no one else has done but feels like it wouldn't be too hard would be finding out how much horsepower she's putting down to get to the velocities that she does, at least at subsonic speeds. There would probably be some assumptions about her size, but I don't know if it'd be too hard to do an flow analysis via FEA in Solidworks to find out what her drag coefficient is and then go from there.
Now that's an idea. At fast enough speeds, water starts condensing in front of her. Forming clouds. Pegasi can interact with clouds as if it were a solid.
Therefore, the recoil is caused by RD being physically bounced back by the accumulation of too much cloud and not enough power, due to how flight magic both are required for speed, and cloud walking, creating a negative feedback loop if not managed properly.
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So if it is all about putting the maximum number of legs forward then why stop at two? Is the next stunt to pull off a four-hoof rainboom?
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They are sucking in air, mixing it with fuel, and igniting to let themselves be propelled forwards by the exhaust? They must have part dragon ancestry.
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Given that slightly different assumptions about how to interpret the scenes we see make a huge difference results, you could get a good-enough estimate just from a basic calculation from the final velocity. Of course a full FEA model would be cooler.
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In Equestria, it seems you can do anything with clouds.