# Shock waves at Mach 470 000

1. Oct 28, 2013

### chasrob

Yep, half light speed or thereabouts; superhero story :). I'm writing a story about this fellow who gets super powers, including super speed. He can move, fly, at up to 100 000 miles per second. He can also move around at normal speed if he concentrates on what he's doing.

Right after he acquired these abilities (he's super strong and invulnerable as well), we find him at an ocean beach at night, sitting on a bench. Thinking his new situation through, so to speak. You know how when you're sitting there, sometimes you take your foot and move it from the ground to your seat, sorta like with your heel on the seat of the bench? Well, the protagonist does this movement but loses his concentration and performs it at half c. IOW, his foot and leg move that fast, 1/2 light speed. He manages to stop before his foot hits the seat when the realization hits him.

The way I have it written: the movement causes a hurricane force shock wave to propogate outwards. Behind him on the boardwalk is some partying going on, a Mardi Gras of sorts in a tourist town. But there is this biggish stone and cement bridge structure immediately behind him that focuses the wave away from the crowd and out toward the surf. Fortunately for him. Unbeknownst to him, however, a beachcomber a few hundred yards away is hurled into pier pilings and killed. It's night OK? He didn't notice the lone person in the dark, no xray vision, heh.

Other than the superpowered magic, does this seem realistic? Or is the situation even more dire for the MC and his surroundings?

Thanks for your help.

2. Oct 28, 2013

### Ryan_m_b

Staff Emeritus
At half the speed of light this superhero has a kinetic energy of 900 petajoules, or 5 times more energy than hits the Earth from the sun every second. If he flies around in atmosphere it would be like trailing several nuclear explosions. That cement bridge is protecting no one.

Is there any particular reason you want him to fly at half the speed of light rather than say...the speed of sound?

3. Oct 28, 2013

### fulltime

I assume he picked up a meteorite that originated in Sagittarius A*, where everything happens at hyper speed due to the presence of a super massive black hole? Local species have to move slightly faster than half the speed of light in order to have a functioning society...

4. Oct 28, 2013

### Staff: Mentor

That means reaction time in the nanosecond range.

5. Oct 28, 2013

### phinds

Shock waves traveling at Mach 470 000 would imply that there is a substance in which the speed of sound is half the speed of light. I do not believe such a substance exists, and I CERTAINLY don't believe that it is the atmosphere of Earth.

6. Oct 28, 2013

### Ryan_m_b

Staff Emeritus
Sorry I assume you're joking but I don't quite get it.

I didn't even think of that, good point.

7. Oct 28, 2013

### chasrob

Yes, the MC has avoided that speed of flight in atmosphere and only plans to do so in space. Reason? The plot demands it. Or strongly recommends, one or the other.

The magic involves him being massless now that he's transformed, which i think would do away with those pesky kinetic energy equations. What insanity I had in mind was that even tho' his (the entity's) body masses zero, the force of him hitting the air molecules is still there and must be reckoned with.

So that was what I meant; his leg is doing the frightful speed... wouldn't it set up a hellacious shock wave travelling at about Mach one?

I have an inkling that it still would be um... explosive no matter what technobabble I used. Even tho' his leg only travels a couple feet.

Last edited: Oct 28, 2013
8. Oct 28, 2013

### Staff: Mentor

If he's massless, then any force applied, at all, would instantly put him at c. Kind of hard to fly through atmosphere when he can't even get a single atom out of the way.

9. Oct 28, 2013

### Hornbein

The speed of sound in neutron star cores is c/2.

10. Oct 28, 2013

### chasrob

That's interesting, sort of like a photon?

Maybe I could have him able to interchange having mass, no mass, or imaginary mass at demand. Or to use the ubiquitous--- "mimick" having mass, etc,

11. Oct 28, 2013

### phinds

Interesting. Who woulda thunk it?

12. Oct 28, 2013

### phinds

Sort of like ANYTHING that has no mass.

13. Oct 28, 2013

### Staff: Mentor

You can do whatever you want. You've already broken the laws of nature so something somewhere isn't going to make sense.

14. Oct 29, 2013

### Aero51

Since you asked about realism, since past Mach~10 the air dissociates and ionizes. Past Mach~15 the air is no longer "air" and is actually a plasma of sorts. I would presume at half the speed of light traveling through a fluid you would initiate nuclear reactions. This can be done when colliding a projectile with a solid such as aluminum at around 10000 mph.

Some research you may want to look into is done by Professor Andrew Higgins at McGill University in Canada.

15. Oct 29, 2013

### Staff: Mentor

16. Oct 29, 2013

### chasrob

I'll google that prof, thanks.

The distance is so short and the time frame is... a couple of nanoseconds? Hard to believe there's time for anything--and its over. Hell of a sonic boom besides?

17. Oct 29, 2013

### Ryan_m_b

Staff Emeritus
If he's massless then he'll travel at the speed of light. Either way though even if he is reducing his mass magically he still is moving at such speed as to rip apart the atoms of the atmosphere creating the effect others have mentioned (i.e. a nuclear explosion)

Doesn't really matter how short the timeframe is. If he's moving his arm through a few litres of air (I think, others can confirm) that he's just initiated nuclear reactions in those few litres. That's got to be at least a couple of kilotonnes worth of explosion.

18. Oct 29, 2013

### Ryan_m_b

Staff Emeritus
Thinking on it I may have a solution to your problem of a superhero so overpowered he can cause nuclear explosions by clapping and destroy the world just by jumping up and down a lot.

You've already written in magic in the sense that he can summon up energy from nowhere and use it to move himself super fast and make him invulnerable. Why not extend it a bit and write that the same magic leeches out into the atmosphere the faster he moves and quickly rearranges all the atoms out of his way. So before his arm rips apart molecules in the air the magic grabs them, accelerates them to high speed, positions them behind his arm and then saps away the energy back to the magic void it came from.

You could even write in limitations like it is harder to do the denser an object is (if you don't want him to get the power to warp through walls) and if the magic field detects liquid/solid it activates a feedback signal that massively slows him down (to prevent the aforementioned nuclear explosions). So he could fly through the air with no disturbance but if he flies into a wall he's decelerated to manageable speeds (i.e less than the speed of sound) and simply smashes through/into it.

How does that sound?

19. Oct 29, 2013

### chasrob

I wish I had the skills of improvisation that you have. That's a much better explanation than I have going. I think I'll [STRIKE]steal[/STRIKE] borrow it, OK?

Regarding the fellow's energy budget, I have him getting it from an exponentially dense space, exterior to and surrounding our multiverse. Dense with Hawking radiation. He got this, from there to here, via a (very long) wormhole.

Lotta problems there. How come he didn't blow up? That wormhole follow him around for a recharge every now and then? Why can't he just use the molehole once and store the energy for future use? If he does that, why doesn't he just blow up? How do you utilize energy storage to walk, talk, fly around, arm wrestle, etc., and do that without blowing up?

Your idea of magic fields giving him feedback and rearranging things is much better, methinks.

Last edited: Oct 29, 2013
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