Flash and Null: What Happens When Gravity is Shut Off?

Falling down is tough, but what about falling up? Or just having gravity disappear in a flash?

In the hunt for the 12 “bus-metas” on the most recent season of The Flash, the series got a chance to introduce metahumans with new and different powers – all of whom bit it to fuel the power of DeVoe, the Thinker. That’s all the spoilers for the season that you get. It was fun, it was serious, it was happy, it was sad, it was…well, it was The Flash. While the CW’s DC Comics-based shows can run the gamut in story, they do remain pretty consistent with tone, and even through everything that happened to him this season, Barry Allen, the Flash, continues to show what it means to be a hero. And just an all-around decent guy, too.

But that doesn’t mean there’s not science that can be done.

So – I’m looking at episode 17 of Season 4 of The Flash, “Null and Annoyed.” In it, we meet Null, a character who was hit by the dark matter at the start of the season. For Null, the matter gave her the ability to manipulate gravity, by touch. Null uses her newfound ability to become (or continue – we don’t know who she was before) a thief.

So yeah – powers over gravity…okay…

Towards the middle of the episode, Barry Allen (the Flash) and Ralph Dibny (who’s disguised as Detective Joe West) confront Null. She touches and gives a push to Barry who starts to float up, towards the ceiling. He’s brought back to STAR Labs where he’s shown to be floating – head up, feet down, and holding on to a bar to maintain his position. Caitlin Snow gives her evaluation – Null’s powers did something to affect the density of Barry’s cells. “It’s like you’ve been filled with helium,” she tells him.

Eventually, the effect wears off, and Barry falls to the floor, following Wells’ prediction. Prior to this, the consensus, as stated by Cisco, was that Null’s power had turned off gravity for Barry – that they needed to find some way to “re-engage the gravitational force” (and we’re going to assume the whole density/“filled with helium” was just a…yeah…that would be really problematic for biology. Superhero scientists can have an off day, just like anyone else).

Let’s go with the larger idea that gravity had somehow been “disengaged” for Barry. It’s a time-honored science fiction gimmick – “turning off gravity.” The thing is – what would that actually be like if it happened to you?

Gravity 101 – For Flashes and Everyone Else

There is a gravitational force between all objects. Planets, cars, you, your cat. Everything exerts a gravitational force on everything else. How much? That’s given – in a simple form – by Isaac Newton’s Law of Universal Gravitation, which looks like this:

F_g = Gm₁m₂/r²

Where:

F_g = the gravitational force between two objects (in Newtons)
G = the Cavendish constant, 6.67259 x 10^-11 N m²/kg².
m₁, m₂ = the masses of the two objects (in kilograms)
r² = the distance between the centers of the masses, squared (in meters)

Just plug the numbers in, and you’ll get the attractive force between any two objects, anywhere in the universe. Seriously. How cool is that? You’re attracted to the earth, but at the same time, the earth is attracted to you. Everything is attracted to everything. But as you can tell by the formula, the size of the force drops off precipitously with distance.

As for the “how” – as in how does the mass of something way out in the solar system affect me – you’re talking about the exchange particles. Gravity is one of the four fundamental forces of the universe (electromagnetic, weak nuclear and strong nuclear round out the rest), and each force is transmitted by a virtual particle. For example, all electromagnetic force (light, heat, etc) is mediated via photons. All weak nuclear by virtual particles called bosons, and strong nuclear by gluons. Gravity’s particles – they’re called gravitons, but as of yet, they haven’t been spotted.  No worries – gravity still works for everything and everyone.

Except Barry, apparently. As Cisco implied, Barry’s not being affected by gravity. Which would not be as cool as it sounds.

What would happen if gravity was disengaged for you? 

Think of this example – you and your friend are standing on the surface of the earth, and suddenly, without explanation, gravity just “turned off” for you. You’ve got no attraction to the earth anymore.

Your friend will keep moving along, on the surface of the earth, like nothing’s changed, because nothing has changed for them. You, on the other hand, and going to start going up. The reason isn’t because no gravity = instant float like Charlie Bucket after drinking the Fizzy Lifting Drink. The reason you’ll start to go up is because you’re traveling in a circle. Or rather, you were.

Think about spinning something above your head on a string. It keeps traveling in a circle because of the constant force toward the center – the centripetal (“center-seeking”) force. No centripetal force, no circular motion. You provide this force by pulling on the string as the object moves around – that pull towards the center is the centripetal force. Now – imagine you cut the string. The object will keep moving – in a straight line starting from when the string was cut. It won’t complete the curve or move in any path but a dead-straight one. That object? That’s you, and gravity was the string.

But why go up?

At the equator, the earth is moving eastward at 463.8 meters/second. You get this by taking the earth’s circumference in meters and divide it by the number of seconds in a day (86400 seconds – 24 hours x 60 minutes x 60 seconds) since earth revolves once in 24 hours. If gravity turns off for you, you’re still (ignoring air resistance) going to be moving eastward at 463.8 m/s, just no longer attached to the surface of the earth. You’ll be travelling in a straight line.

To your friend on the ground, you’re going to start to slowly rise, because the earth is round. Your rate of rise depends upon how far the earth curves away from you per second. Again, the earth rotates once per day – 360° in 24 hours (86400 seconds). So in one second, the earth rotates 360°/86400 seconds = 0.004°/second. Let’s set up the trigonometry:

To find the height (the side of the triangle opposite of our angle of 0.004°) we want the sine of that angle, because (remember SOH CAH TOA?):

sin (0.004°) = x/463.8 meters

Solve for x:

x = sin (0.004°)463.8 m

x = 0.032 m

x = 3.2 cm/second

Turn off gravity, and you don’t shoot into the sky. You putter upward at 3.2 centimeters a second. In a room with a 10-foot (3.05 m) ceiling, you’d hit it in a little over one and a half minutes, because time = distance/speed.

If you’re not being acted upon by any force, your motion would be constant rather than accelerated. Constant up from the frame of reference of someone on the ground. Which means you wouldn’t be squished when you hit the ceiling. Nothing is “pulling” you up. You’re rising because nothing’s holding you down and the floor is moving away in a circle.

Let’s bring this back to Barry, who’s floating free, with gravity disengaged. Central City’s not at the equator, so what effect would that have on his ascent? Velocity upward in this situation would decrease by the cosine of the latitude, or how far you are away from the equator. The earth is spinning fastest at the equator, and it gets slower as you move towards the poles (the circumference at a given latitude is less than that at the equator, but still goes around in 24 hours, so the velocity has to be less – you’re travelling less distance in the same amount of time). Which begs the question: where is Central City?

Historically in comics, Central City has been in American Midwest, and has been put as an analogue to Kansas City, MO, the latitude of which is 39° North. So…

cosine(39°) = .78

(.78)(463.8 m/s) = 361.8 m/s

Run the same calculations as we just did for the equator, and you’ll find that Barry – if gravity was just “turned off” would have been rising at 2.5 cm/sec, a little less as if his gravity had been turned off at the equator.

What was shown of Barry’s floating up after Null touched him looked pretty accurate. “Turning the gravity off” on a  person would result in a light upward float, and they would also be able to be pushed around with ease. In Barry’s case, Null disengaged the gravity acting on him and pushed him up. With no gravity hold him down or help to create static friction, he was completely at the mercy of her push, and quickly rose to the ceiling. Without gravity, any force – from a breeze to a nudge would be enough to send you moving in the direction of the force, and that’s a problem. A strong exhale would provide propulsion in the opposite direction you’re blowing. Your life would become a living testament to Newton’s Laws of motion. 

Unless you were standing perfectly still on a windless day, some force would be acting on you. If you (or say, the Flash) was running, your final step on the ground will push you up faster than you’d just float. Any rescue attempt would send you off on all new vectors with different directions and speeds. Your physics teacher would love having you around for demonstrations of vectors and Newton’s Laws, but you probably wouldn’t enjoy it so much. 

Oh, and the idea that the effect was caused by The Flash’s eponymous “dark matter,” and that it would just wear off and gravity would just turn back on again for Barry…well…okay. That’s some DC Universe superscience, there.

And I’m Free – Free-Floating…Up

If you ever find that gravity had been turned off for you, and you were rising at about 3 cm/sec…when would this stop being cool and start being a problem?

3 centimeters per second is about .1 kilometers per hour, so you’ve got plenty of time to hang out before some real problems start. If nothing’s pulling you down, you still have mass, you’d start to be pushed around by the winds, which would pick up the higher you went. At 1 km high (about 10 hours of rising), things would be very chilly, and the wind will really start to push you along.

At around 2 km high (about 20 hours of travel time up, and perhaps enough time for you to have become a national news story, and someone to have tried a rescue…), the temperature has dropped below freezing, and your exposed skin is at risk of frostbite. Oh, and the oxygen density has really dropped off – making it hard to catch your breath, and probably making you kind of sleepy. But hey, the view is petty spectacular.

You’d also have all the problems astronauts on board the ISS have as well when it comes to “zero g.” Let’s say everything about “you” has no gravity. If you’re upset about your situation and cry, your tears wouldn’t fall anywhere, they’d blob up on your eye, water’s surface tension would be the dominant force, not gravity. Circulation would be a little weird and different because it’s not relying on gravity to help pull blood downward – you’d probably get a little stuffy and your face would be a bit swollen, compared to normal. And I hope you went to the bathroom before gravity turned off for you. 

You’d still be able to breathe though, but the air would be well below freezing from here on up. At 8 km (80 hours of rising – hey, how are you getting food?), you’ve reached the death zone. There’s not enough oxygen at that height (and above) to support human life. After that, you’ll just be a frozen, slowly-rising corpse.

But hey – you had a lot of time to get there, and probably saw some incredible sights as the earth continued to spin underneath you, and you were carried along by the winds.

You’ll notice – it’s not dramatic at all, is it? A slow, lazy drift upward, pushed around by breezes to your inevitable death by asphyxiation. Gravity’s not dramatic – just always there. Always pulling. Not terrifying by any means. You want terrifying? You know what you need…

Reverse-G: The Scariest Villain Ever.

In the episode, it appeared that Null had some control over her abilities – that it, she could “tune” how much gravity or “reverse gravity” she gave to the objects that she touched. In DC Comics, Null’s powers are similar in that he (Null’s male in the comics) can “turn off” gravity for objects – letting them fall later. In the episode, objects weren’t just “weightless” as Barry appeared to have been – they rose and fell with different accelerations, suggesting that Null has some ability to “tune” the gravity her victims are experiencing, both strength and direction.

How do I know this? I used the formulas below for yourself on the scenes with Null in the episode and solve them for gravity. This effect is easiest to see when objects touched by Null rise way too fast to just have had their gravity “disengaged.”

If that was the case – that Null did have full control over the effect of gravity on an object or person, oh…the wasted potential. A villain that could reverse or otherwise change the direction of gravity – without changing the value of the acceleration, even – would be deadly. That’s because gravity is accelerated motion – falling things fall faster and faster.  

If Null wanted to be truly terrifying, all she had to have done was reverse gravity for Barry – make him accelerate at 9.8 m/s² up, not down. To figure out why this would be horrible, let’s pull out a kinematics formula:

For instance: d = 1/2gt² and v²=2gh

Where d = distance (up in this case), g = gravity, t = time, v = velocity and h = height. 

If Null reversed gravity, and Barry fell up for six seconds? He’s 176.4 meters above the ground. If she turned her power off and Barry fell from that height, his final velocity would be 58.8 m/s, or 131.5 mph. That’s a fatal 12 second rise and fall (six seconds up and six seconds down). Hit someone with that same power in a room with a 10 foot ceiling, and you’re slamming them into the ceiling at 7.7 m/s, or 17.2 mph.

Same if you could “turn” gravity in whichever direction you wished. Someone is 3 meters away from the wall to their right? Make that right wall the “floor” in your victims’ frame of reference, and they slam into it in just under second – all due to the physics of accelerated motion.  Acceleration is not your friend.

But if Null – or you…just saying, if you ever find yourself with these abilities – really did have control over gravity, she didn’t need to become a villain to make money. One call to Elon Musk, or anyone else trying to get materials into space, and her days of scraping by with smash and grab jewelry heists would have been over. She could put rockets up into space(*) with zero fuel cost and bring them back down again and charge whatever she wanted. And she’d probably get benefits, too. 

(*)  – slight spoiler, by using Null’s powers, DeVoe was planning to place a series of satellites into orbit around earth. 

I Teach STEM – How Can I Use This? 

The effects demonstrated by Null in “Null and Annoyed” aren’t that bad at all when it comes to gravity, forces and free fall…once you accept the idea that gravity can be shut off. Aside from asking students to figure out what would happen to a person if gravity was “turned off” for them (a great way to tackle a misconception they may have gained from movies and TV), there are a few other scenes with Null that can be used or worked out: 

1. Null’s first appearance and the robbery at the Museum (yes, where Jay and Silent Bob are security guards – Kevin Smith was the director of this episode). Null sends the crate up, and then has it crash back down. What was its acceleration up? How far up must it have been for it to crash down at 55 mph, as Barry suggested?

2. Inconsistencies with Barry’s floating and body position in STAR Labs. If he had zero gravity, why was he positioned like he was? Why could we see the strain on actor Grant Gustin’s face while he was “floating?”

3. The hostage car that Null always floats nearby. That’s a lovely freefall problem.

4. The final scene with Null – Barry flies upward, and Team Flash is tracking the suit’s telemetry. Do those numbers work? What about Ralph’s rescue plan? Would an airbag Ralph have been enough to stop Flash falling from that height without injury? 

And that’s just the start. Start looking at the episode with a little more detail, and you’ll be able to pull out the tons of force and motion ideas as well.