If you had to travel At the Speed of Force, how fast would you have to go?

THERE WILL BE NO SPOILERS FOR ZACK SNYDER'S JUSTICE LEAGUE, OTHERWISE KNOWN AS THE SNYDER CUT.

Hello, I'm Sasi, This is Unnecessarily Complicated, and I just watched Zack Snyder's Justice League on the other day. Yeah, it was long, but it had it's moments. And the same can be said about the score. Sure, there was that new Wonder Woman theme, but then Flash got his new theme that was cool. (Seriously, Junkie XL has been putting out atleast one amazing track per DCEU Film he's worked on. What are you going to do when you're not saving the world? from Man of Steel, Is she with you? from BvS, and now ZSJL's At the Speed of Force.)

And I heard At the Speed of Force online, completely out of context, just the music. And now I'm listening to the 1 hour looped versions, on loop, and I can't get this song out of my head. If you haven't heard the song, here's the link, so you can listen to it while reading the post. But that title raises a question. What is the Speed of Force?

The origins of it's phrase go back to the comics, where there's a Extra-dimensional energy called the Speedforce, which the Flashes use to draw their strength from. Green Lanterns have the emotional spectrum, Nova Corps have the Nova Force, Jean Grey has the Phoenix Force, and like that, Flash has the Speed Force.

It's this connection with the Speedforce that allows him to go as fast as he does. In the CW's The Flash, and many times in the comics, it's depicted as a separate dimension, where you can freely enter and travel through, and come out at any other point in space and time.

But that's not a force. It's a separate universe. This is a dead end.

So, probably the best way to think about this, is how long does it take for something to be affected, once a force is applied? 

To answer that, we need to first understand what kind of a force?

Forces can be broadly classified as Contact and Non-Contact Forces, and the answer changes based on them.

Contact forces are those, where there is physical contact between the Force applier, and the object. Things like Friction, You pushing the mouse on the mousepad, walking, jumping, etc.

Non Contact forces are those where there's no physical contact between the objects that experience force. Things like, Gravity or Electromagnetism are examples.

Our best understanding of the Non-Contact forces is through the Standard Model. Oversimplifying things, each force has a carrier particle, and the effects of the force are transferred through these carrier particles. For Electric and Magnetic Forces, it's through Photons. For Gravitational Force, it's the theorized Graviton.

Because of this, the speed of these forces has a hard limit, at the speed of these particles. If a new charge spontaneously appeared somewhere, its field will appear at a distance, only when the carrier particle, the photons, appears at that spot. So, the speed of electromagnetic forces is the speed of light.

Now, gravity is a bit of a weird case. The gravitational force is calculated to travel at the speed of light, and we've observed Gravitational Waves moving at the speed of light. You might have heard about the Eight-minute delay between the Sun Disappearing, and the earth going off orbit. Unfortunately, there's no confirmed theory explaining how gravitons might work. Yet. Scientists and Theorists are actively working on that, and this is in fact the biggest focus of the grand unified theory.

Now the speed of contact forces has been a cornerstone of the debate around trying to get things, specifically information, to travel faster than the speed of light.

A common method to "break the light barrier", is to take a stick, of let's say, one light-second long. (About 300k Kilometers). If we swing this long stick, the other end will move as soon as we move this end we're holding. It should take one second for that to happen, but the entire stick starts moving at the same time.

Here's the thing, in a perfectly rigid body, it's what would happen. But unfortunately, there's no perfectly rigid body in the world. And any force you apply, only applies to the molecules in direct contact with it. It's this little displacement that travels as a deformation wave and moves the entire particle. And, in fact, it doesn't need something extremely long for the speed of this deformation wave's speed to show itself. Here is a slo-mo video of a golf swing. Albeit very little, you can see the effects of this as the stick bends due to this effect.

On something larger, that effect is going to be a lot more apparent. (And if you want to big brain and tell that this is the speed of torque, the same effect happens when you push at one end of the stick. So the Speed of Force and Speed of Torque is really the same since we're trying to find the speed, based on the time delay between the action and result)

So then, what is this speed of force?

Well, since this force is moving as a deformation wave of compression in the material, finding the speed of this compression should give our answer. And luckily, we know another wave that moves in compressions and rarefactions. Sound Waves. The Speed of a contact force is really the speed of a compression wave, or a sound wave, in a specific medium.

Okay, but is the title justified given what we see the Flash do?

Assuming the Speed of Force in the title refers to a non-contact force, it's absolutely justified. Flash says he's going a lot faster than what speed we're getting for the non-contact forces, to do what he does in that scene.

Not only is it a beautiful scene in a cool movie, with an amazing soundtrack. The Title of the soundtrack serves both as a pun on the character's source of power, a nod to the comics, and also is scientifically accurate.

I'm not saying ZSJL is perfect. But it does do a lot of things right.