Serious Scientific Answers to Absurd Hypothetical questions

[ARS]

AK47 rounds have an energy of 1,991 J per bullets. A single AK47 magazine contains 30 bullets, totalling 59,730 J. Assuming you didn't brace the recoil, you will be pushed by the total force of 59,730 J to the opposite direction. The only thing that's missing is a factor of your mass and the friction on the floor in order to calculate the distance travelled

Edited December 11, 2017 by ARS

[kerbiloid]

AKM (AK47 is just a fake name for an East-Asian counterfeit) bullet mass = 7.9 g, velocity = 715 m/s.
Total impulse = 7.9*10^-3 * 715 * 30 = 170 kg*m/s.

If the body mass = 85 kg, delta-V = 170/85 = 2 m/s.

[DDE]

3 hours ago, Spaced Out said:

If you sat in an office chair and fired an AK-47 that was placed so the thrust from recoil would be directed through the Center of Mass, how far would you move per shot?

Start here: https://what-if.xkcd.com/21/

[ARS]

There are redout and blackout effect caused by high-G when going at highspeed maneuver, but mostly it's during prolonged maneuver such as "pulling up from steep dive at high speed before the pilot start to faint". But what happen when it's instantaneous sudden maneuver like this:

At that kind of maneuver, what kind of effect that'll be inflicted on human body by the sudden change of G-force?

[MatterBeam]

6 hours ago, ARS said:

There are redout and blackout effect caused by high-G when going at highspeed maneuver, but mostly it's during prolonged maneuver such as "pulling up from steep dive at high speed before the pilot start to faint". But what happen when it's instantaneous sudden maneuver like this:

At that kind of maneuver, what kind of effect that'll be inflicted on human body by the sudden change of G-force?

Car crash levels of damage. Massive bruising, concussions, joints popping, ribs breaking, and at even higher levels, you get organ and blood vessel rupture. Its not pretty.

[TheSaint]

19 hours ago, ARS said:

150 years is a very long time. Things got claimed by marine life VERY FAST. Salvaging the sunken ships for metals is not worth the price and effort. The metal would be barely recognizable and poor quality because of rust and getting rid the corals that grew around it is simply too much hassle when all you want to get is just metal. The most that you can get is science, but that can be done without lifting the whole ship to the surface. Sunken ship becomes an underwater ecosystem for a variety of marine life. Lifting that ship isn't gonna be a good idea, since you potentially destroying that ecosystem. Aside from that there's an unwritten rule for sailors to simply left the sunken ship underwater and not disturbing it to honor those who died aboard the ship and sunk with her

Actually, there is a very good reason to salvage steel from very old shipwrecks: Low-background steel. All steel that has been produced since the advent of above-ground nuclear testing is contaminated with minute amounts of long-lived radionuclides that are suspended in the atmosphere. You can stop holding your breath, they are present in such small amounts that they pose no hazard to human health. But what they do present a problem for is apparatus that are designed to detect very minute amounts of radiation. So any such device needs to be constructed out of steel that was produced prior to 1945. One of the most common sources of such steel is shipwrecks, including (as pointed out in the linked article) the German WWI High Seas Fleet that was scuttled at Scapa Flow.

14 hours ago, kerbiloid said:

AKM (AK47 is just a fake name for an East-Asian counterfeit)

Just to be pedantic, the AK-47 was the original Soviet assault rifle that was produced in 1947. The AKM was the improved model that was introduced in 1959. The AKM was produced in far greater numbers than the AK-47, and when most people picture an AK-47 what they are probably picturing is an AKM or a clone thereof. But the AK-47 was actually produced and fielded by the Soviet Union for 12 years as their front-line assault rifle.

[kerbiloid]

10 minutes ago, TheSaint said:

But the AK-47 was actually produced and fielded by the Soviet Union for 12 years as their front-line assault rifle.

That was AK. Without 47 or M. Manufactured and fielded since 1949, not since 47.
Original "AK-47" was not being manufactured in amounts, it was an experimental party.

Edited December 11, 2017 by kerbiloid

[Zeiss Ikon]

20 hours ago, Spaced Out said:

If you sat in an office chair and fired an AK-47 that was placed so the thrust from recoil would be directed through the Center of Mass, how far would you move per shot?

A while back (in this thread, I think) I calculated that a 10 mm round would push 100 kg of shooter and space suit around .05 m/s.  Coincidentally, the 7.62x39 round has a similar momentum -- instead of a 180 grain bullet at 1600 ft/s, it's a 100 grain bullet at around 2300 ft/s.  You'll get a little more rocket effect from the gas with the AK (due to higher pressure when the bullet leaves the bore) than with the 10 mm pistol, but that's hard to quantify.  So, you, rifle, and office chair mass (not surprisingly) close to 100 kg.  You fire one round, and get pushed to a speed of 2-3 inches (.05 to .08 m) per second, and if the floor is very smooth and level, and the chair's casters in exceptionally good condition, you'll move a few inches.

Of course, if you unload a whole 20 round magazine as rapidly as the (USA minimum hassle) semi-auto mechanism will function, you ought to be able to get up to around 1.5 m/s -- about average walking speed -- and that would let you coast (very roughly) five or ten meters before friction brings you to a stop.

Edit: I'm not a Kalashnikov expert.  If it's a 30 round magazine, you'll get 50% more velocity.  Hope those casters are in good shape and that floor's clean -- if a caster hits a piece of junk that acts like a wheel chock while you're rolling at 2+ m/s, you might take a tumble.  Fortunately, the rifle you're carrying will have an empty magazine by that time.

Edited December 12, 2017 by Zeiss Ikon
magazine capacity

[DDE]

8 hours ago, Zeiss Ikon said:

Of course, if you unload a whole 20 round magazine as rapidly as the (USA minimum hassle) semi-auto mechanism will function, you ought to be able to get up to around 1.5 m/s -- about average walking speed

You require additional dakka.

[Green Baron]

Gawd is it really necessary to show weapons of potential mass murder here in this little game forum ?

Kindly asking for a little sensibility .... :-)

Edited December 12, 2017 by Green Baron

[0111narwhalz]

5 minutes ago, Green Baron said:

Gawd is it really necessary to show weapons of potential mass murder here in this little game forum ?

Kindly asking for a little sensibility .... :-)

Hard to argue that rockets don't fall under that, considering their historical origins.

[Green Baron]

6 minutes ago, 0111narwhalz said:

Hard to argue that rockets don't fall under that, considering their historical origins.

That would be political. But rockets without warheads are so cute ... :-)

[DDE]

1 hour ago, Green Baron said:

Gawd is it really necessary to show weapons of potential mass murder here in this little game forum ?

Two words: BD Armory.

BRRRRRT!

[raxo2222]

5 hours ago, Green Baron said:

Gawd is it really necessary to show weapons of potential mass murder here in this little game forum ?

Kindly asking for a little sensibility .... :-)

Not to mention antimatter fuel, xray "laser" beams and RKV/Warp Drive ramming into planets *cough* Interstellar Extended mod *cough*

[Diche Bach]

@Zeiss Ikon, @ARS, @TheSaint Neat! Good posts

Got a new one  . . . Was watching a YT about James Webb and of course the issue that looking far away = looking back in time arose. Had a crazy thought occur to me but I'm sure one of you will be able to clear it up.

Would it be possible to look at the same astronomical object at TWO (or perhaps) more different times by pointing a telescope in two distinct directions? The microwave background radiation seems in a way to be reflecting this principle.

What if we could literally look back at the Earth a couple billion years ago by some black magic of astronomy!?

Edited December 12, 2017 by Diche Bach

[Gaarst]

18 minutes ago, Diche Bach said:

Would it be possible to look at the same astronomical object at TWO (or perhaps) more different times by pointing a telescope in two distinct directions? The microwave background radiation seems in a way to be reflecting this principle.

Not sure what you mean there. If you look in two different directions you'll see two different objects. The CMBR is a bit of an exception but it's not an object in itself, and even then it's not perfectly homogeneous.

Quote

What if we could literally look back at the Earth a couple billion years ago by some black magic of astronomy!?

You can't. If you want to see the Earth 1 billion years ago, you have to observe it from 1 Gly away. Since you need more than 1 billion years to travel 1 Gly, at best you'll be able to observe the Earth as it was shortly after you left.

That or you find a way to travel faster than light.

[Diche Bach]

Well indulge me just a bit more on this . . . Let us project where (relative to our current position in the cosmos) the Sol system was 1 billion years ago, and then point our telescopes there. As you have pointed out, We will not see Sol there because our trajectory from there to here is not of the proper shape and velocity. Consider that for a moment. I would imagine it should be possible for an object moving through space time to travel on an arc of sufficient curvature and speed that it arrives at a point in its future sufficient to look at itself in the past no?

I suppose that is really the question I'm getting at: What sort of trajectory and speed would be required for an observer to be able to look back at themselves at an earlier point in time?

ADDIT: and no I haven't been dipping into the Magic Mushroom Egg Nog prematurely. Perhaps a bit too much C++ on the brain, but nothing pharmacological 

Edited December 12, 2017 by Diche Bach

[sevenperforce]

34 minutes ago, Diche Bach said:

@Zeiss Ikon, @ARS, @TheSaint Neat! Good posts

Got a new one  . . . Was watching a YT about James Webb and of course the issue that looking far away = looking back in time arose. Had a crazy thought occur to me but I'm sure one of you will be able to clear it up.

Would it be possible to look at the same astronomical object at TWO (or perhaps) more different times by pointing a telescope in two distinct directions? The microwave background radiation seems in a way to be reflecting this principle.

What if we could literally look back at the Earth a couple billion years ago by some black magic of astronomy!?

Actually, yes. It's rare, but it can happen. A distant galaxy cluster bends light from even more distant objects around itself. If we are nearly lined up with both objects, then we can sometimes see multiple images of the same object. When we are perfectly lined up, this produces an "Einstein ring":

The blue ring is the image of a single object exactly on the other side of the central cluster.

When we're almost (but not quite) lined up and the mass distribution of the lensing object is just right, we get multiple discrete images. The most famous is the Einstein cross:

The light from the actual object takes four discrete paths to wrap around the galaxy on its way to us. Since those paths differ in length, what we are seeing here is a single object at four different points in time. The image on the left is the youngest, followed by the image on the bottom, then the one on the top, and finally the one on the far right.

This could get really interesting if, for example, there was a hypernova in the actual object. We'd see an extra flash of light first from in the left image, then in the bottom, then the top, then the right, based on the difference in the path lengths for each image.

If I recall correctly, this has recently been used to watch a "replay" of a supernova. We saw a fairly close supernova in one image and recognized that we could expect it in the other image just a few hours later, so we had time to train several telescopes exactly on the spot and get some really good data.

Now, the maximum amount of time difference between any two images is a function of the ray path length, so there's a limit to how much delay is possible. And light wouldn't be able to curve around a 180-degree lens and come back to us, so we can't image prehistoric Earth that way.

[Diche Bach]

So given the speed of light, what trajectory would an object have to achieve (arc and velocity I reckon) in order to "catch up to" light it reflected at some point in its past, i.e., to "see itself in the past."

[sevenperforce]

18 minutes ago, Diche Bach said:

So given the speed of light, what trajectory would an object have to achieve (arc and velocity I reckon) in order to "catch up to" light it reflected at some point in its past, i.e., to "see itself in the past."

That question doesn't compute.

[magnemoe]

12 minutes ago, sevenperforce said:

That question doesn't compute.

it does, but it involves inventing an faster than light drive and then figure out the physic of it by testing it.  
Details is left for above poster. 
 

[Diche Bach]

Well, speeds of say  . . . 30% c are 'tenable' no? VERY costly, and "out of reach" in being stuck at the conception stage, but tenable it seems. I don't have the knowledge to say just how fast one might go with actual existing technology (but assuming things like: a One World Government, no corruption, graft, waste or profiteering and a citizenry who are almost uniformly devotees of science and eager to devote 50% of their earnings to fund Humanities interstellar endeavors).

Perhaps with enough money and time speeds even on the order of 90% c are possible!?

So now let us imagine we have such a space craft traveling along in a specific trajectory (somewhere between Neptune and the Oort Cloud and effectively "in orbit" of the galactic center and just slightly prograde of the orbit of the Sol System itself.

The ship is reflecting light from the various luminous objects in the universe and (depending on albedo, shape, etc.) reflecting in pretty much every direction (including prograde and the full cone we might consider "forward" around prograde). Even though it is traveling at 90% c it is still not fast enough to "catchup to" the image of itself which it is projecting forward (nor in any other direction). Light is moving faster than it is so it cannot catch up to its own projection by simply going forward.

But what if it makes a turn at point t along its original trajectory? The light it was reflecting at point t will go spreading through the cosmos more or less eternally, but it will always move in straight lines from point t (omitting the fact that it could be blocked, reflected, refracted or whatever).

I suppose what you are all telling me is: without exceeding the speed of light it is not possible for the space craft to catch up to the light it projected at point t. You are probably correct, but this was the "thought experiment" I had in mind. "What would it take" for the space craft to catch up with its own image and see itself as it looked at point t?

Edited December 13, 2017 by Diche Bach

[Steel]

7 minutes ago, Diche Bach said:

I suppose what you are all telling me is: without exceeding the speed of light it is not possible for the space craft to catch up to the light it projected at point t. You are probably correct, but this was the "thought experiment" I had in mind. "What would it take" for the space craft to catch up with its own image and see itself as it looked at point t?

You've answered your own question there. You'd need to find a way to travel faster than light.

[Diche Bach]

6 minutes ago, Steel said:

You've answered your own question there. You'd need to find a way to travel faster than light.

 but . . . but What about the curvature of space-time continuum or some shiz!? Surely!? . . . 

Physics is a harsh mistress . . . 

Doesn't the Alcubierre drive essentially require either (a) a ~Nanogram of dark energy, i.e., infinitely more than we can be 99.99% confident even exists, else (b) infinite baryonic energy?

Harsh realities like this lead me to entertain the idea that there really is a supreme being responsible for it all, including the evolution of our consciousness . . . butinstead of it being a benevolent Northern Euro Beardy guy or a Flying Pasta creature, it is really . . .

Edited December 13, 2017 by Diche Bach

[DAL59]

1 hour ago, Diche Bach said:

Nanogram of dark energy

Negative Energy.  A few tons of it, too.