## Science-based what-if questions

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Eebster the Great
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### Re: Science-based what-if questions

I mean, if it has infinite density and finite, nonzero volume, then by definition it has infinite mass.

andykhang
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### Re: Science-based what-if questions

Also, if that thing have finite mass, then technically it would be made out of infinite of infitestimal with force infinitely close to zero.

Edit: Singularity here is more like in a math sense than a physics one. Weird point of math, is what I'm saying here, it you get my drift

Eebster the Great
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### Re: Science-based what-if questions

andykhang wrote:Also, if that thing have finite mass, then technically it would be made out of infinite of infitestimal with force infinitely close to zero.

I'm not sure what you mean. The idea of continuous matter is that a pure element is made of nothing but itself and is the same at all scales. (The latter point is the real problem, incidentally.) I don't know which force you're involving here.

Edit: Singularity here is more like in a math sense than a physics one. Weird point of math, is what I'm saying here, it you get my drift

Why would there be a singularity?

Soupspoon
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### Re: Science-based what-if questions

I think the 'singularity' would be in the first-or-more order derivative of 'thingness'. A hard edge of 'whatever' (say a "solidity field", as I had originally envisaged it) would mean an infinite slope/point of inflection from "nothing" to "something". Or so I interpret AK's "singularity in a mathematical sense". Or else closely related to the "AI singularity" (which is really the Event Horizon, as I think I've suggested at another time in another thread!) in that it's a boundary between universe-as-we-know-it and Here Be Dragon (i.e. as a Mass Noun/continuum).

andykhang
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### Re: Science-based what-if questions

Eebster the Great wrote:
andykhang wrote:Also, if that thing have finite mass, then technically it would be made out of infinite of infitestimal with force infinitely close to zero.

I'm not sure what you mean. The idea of continuous matter is that a pure element is made of nothing but itself and is the same at all scales. (The latter point is the real problem, incidentally.) I don't know which force you're involving here.

Edit: Singularity here is more like in a math sense than a physics one. Weird point of math, is what I'm saying here, it you get my drift

Why would there be a singularity?

Sorry, I kinda talk wrong here. What I mean is, if the thing is finite, yet could scale infinitely smaller without finding gap, then if you split this thing into infinite little piece, each piece would be the same object infintitely smaller, with infinitely less thing going on for it as any scale (less force, less mass, etc...)

Eebster the Great
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### Re: Science-based what-if questions

If we step away from infinity, the point is that at any given scale, all extensive properties will be scaled similarly, so there will be no qualitative difference. In such a universe, there would be no particular reason the Earth should be 12,700 km in diameter rather than 12,000,000 km or 12 km or 10-100 km.

andykhang
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### Dark Matter Black Hole

Supposed I gather all the dark matter in the Milky Way galaxy into one place close to Earth. Would it become a black hole, if so, is it any different? (Probably not, I assume)

Tub
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### Re: Science-based what-if questions

A dark matter black hole may or may not be a tiny bit darker than a regular black hole

Seriously, if you put heavy stuff within a region smaller than its schwarzschild radius, then you'll get a black hole. Dark matter has mass, so it'll work. From the outside, it won't look any different - all you can see is thermal radiation from the event horizon.

Soupspoon
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### Re: Science-based what-if questions

Given we don't yet really know what Dark Matter is (including possibly a mere artefact of some other misunderstanding yet to be fully identified and dealt with, but not matter at all) we may find that 'real' Dark Matter isn't the kind of stuff that would willingly clump together in that way. The above is as good a summary of what we might expect. But also be prepared to be surprised as things (seem to) become clearer about the stuff.

cyanyoshi
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### Re: Science-based what-if questions

There appears to be an order of magnitude more dark matter in/surrounding the Milky Way than the non-dark kind, so bringing it all in one place would seriously disrupt the structure of the whole galaxy and spell disaster for the Solar System. The Schwartzchild radius of that black hole would be between 0.1 and 1 light year, going all the way out to the inner edge of the Oort cloud.

Sableagle
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### Re: Science-based what-if questions

According to Bulbapedia,
Gardevoir is able to see the future using its psychic powers. Additionally, it is able to create small black holes, distort dimensions, and support itself without feeling the pull of gravity.

Just how small would a black hole have to be for it to be useful in a one-on-one fight and not count as a weapon of mass destruction?

Well, obviously it's a weapon of destructive mass compression, but let's take the example of some fool in a car trying to intimidate me and my pet Gardevoir while we're out cycling (would I need to buy a tandem for that?) and her defending me by creating a small black hole inside his crank-case. Just how small would it have to be to not wreck me?
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gmalivuk
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### Re: Science-based what-if questions

The smallest black holes all evaporate through Hawking radiation pretty damn quick, so you just need to decide how much energy you want the explosion to have and then create a black hole with the equivalent amount of mass.

Anything big enough to have macroscopically noticeable effects from the curvature of spacetime is going to be a WMD.
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Sableagle
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### Re: Science-based what-if questions

E = mc2 conversion? So for 10 kJ I'd need a 10000 / c2 kg black hole?

A 111.265 pg black hole. Umm ... around a billion atoms?
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andykhang
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### Black hole bomb

So yeah, supposed you're building something like that and purposedfully trigger it for it to explode (probably the fastest way to completely evaporate a black hole, tbh). Suppose that you also want to vaporize the black hole in it entirely, how thick would the enclosement need to be in other for it to hold it long enough before an Earth-size black hole release all it energy?

gmalivuk
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### Re: Science-based what-if questions

This calculator says an Earth-massed black hole would take 5.67x1050 years to evaporate.
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andykhang
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### Re: Science-based what-if questions

Earth-size (as in, diameter), not Earth-massed. Turn out, you can't build a black hole bomb if that thing is too small.

gmalivuk
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### Re: Science-based what-if questions

Bigger takes longer, and an earth-radius black hole would require almost a billion Earth-masses (and would take 2x1077 years to evaporate).

Edit: Of course, any black hole that's warmer than the temperature of radiation falling on it is going to grow, not evaporate, and the coldest you'd find in space is the temperature of the CMBR itself, which means any black hole bigger than about 1% of Earth's mass won't evaporate at all until the universe itself cools down sufficiently.
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p1t1o
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### Re: Science-based what-if questions

Sableagle wrote:According to Bulbapedia,
Gardevoir is able to see the future using its psychic powers. Additionally, it is able to create small black holes, distort dimensions, and support itself without feeling the pull of gravity.

Just how small would a black hole have to be for it to be useful in a one-on-one fight and not count as a weapon of mass destruction?

Well, obviously it's a weapon of destructive mass compression, but let's take the example of some fool in a car trying to intimidate me and my pet Gardevoir while we're out cycling (would I need to buy a tandem for that?) and her defending me by creating a small black hole inside his crank-case. Just how small would it have to be to not wreck me?

If Gardevoir is capable of conjuring objects inside his crank case, it really wouldnt have to be a black hole to wreck his day.

How about just a modest sized iron canonball?

Tub
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### Re: Science-based what-if questions

p1t1o wrote:If Gardevoir is capable of conjuring objects inside his crank case, it really wouldnt have to be a black hole to wreck his day.

How about just a modest sized iron canonball?

How about 1kg of glitter in the driver's compartment?

gmalivuk wrote:Bigger takes longer, and an earth-radius black hole would require almost a billion Earth-masses (and would take 2x1077 years to evaporate).

Edit: Of course, any black hole that's warmer than the temperature of radiation falling on it is going to grow, not evaporate, and the coldest you'd find in space is the temperature of the CMBR itself, which means any black hole bigger than about 1% of Earth's mass won't evaporate at all until the universe itself cools down sufficiently.

The black hole bomb from the video encloses the black hole in a mirror dome and accelerates the radiation in the ergosphere. Suspending the black hole in a bath of high temperature radiation is not going to expedite evaporation.

In practical terms, the limit of the bomb is not going to be the size of the black hole, but the quality of the mirrors, and your ability to keep them at a constant distance to the black hole. Rigid hollow spheres around point masses aren't stable.

p1t1o
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### Re: Science-based what-if questions

A black hole bomb could never be any more powerful than a matter/antimatter annihilation bomb of equivalent mass, so unless your target is gas-giant sized, thats probably your first choice.

I can't think of any interesting way to use a black hole on a car-sized target without reducing most of the planet to expanding plasma, or incorporating it into the black hole itself.

But I wonder what the lethal concentration of glitter in air is?

Sableagle
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### Re: Science-based what-if questions

I found a website that sells 0.008, 0.015, 0.035 and 0.040 glitter, among other sizes I can't see because of all the pop-ups, so I closed that tab again.

"Hi! Your website pissed me off, so I shall not be shopping with you or recommending you to friends ... ever."

I'm inclined to guess they mean inches, because if they mean mm those are bacterial sizes.

0.008 inches is 0.2032 mm, so we're still looking at small stuff.

The much more reasonable .gov sites (maybe they don't pay enough to get annoying pop-ups and faders, or maybe they've actually got more sense) for particulate matter list some sizes:
Particle pollution includes:

PM10 : inhalable particles, with diameters that are generally 10 micrometers and smaller; and
PM2.5 : fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller.
How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle.
[/quote]Three urban environments, office, apartment and restaurant, were selected to investigate the indoor and outdoor air quality as an inter-comparison in which CO2, particulate matter (PM) concentration and particle size ranging were concerned. In this investigation, CO2 level in the apartment (623 ppm) was the highest among the indoor environments and indoor levels were always higher than outdoor levels. The PM10 (333 µg/m(3)), PM2.5 (213 µg/m(3)), PM1 (148 µg/m(3)) concentrations in the office were 10-50% higher than in the restaurant and apartment, and the three indoor PM10 levels all exceeded the China standard of 150 µg/m(3). Particles ranging from 0.3 to 0.4 µm, 0.4 to 0.5 µm and 0.5 to 0.65 µm make largest contribution to particle mass in indoor air, and fine particles number concentrations were much higher than outdoor levels. Outdoor air pollution is mainly affected by heavy traffic, while indoor air pollution has various sources. Particularly, office environment was mainly affected by outdoor sources like soil dust and traffic emission; apartment particles were mainly caused by human activities; restaurant indoor air quality was affected by multiple sources among which cooking-generated fine particles and the human steam are main factors.[/quote]

Now to try to find details about how toxic those are without screaming at a website.

Dear gods. "These data indicates ... "

Finally:

US Midsize cars have internal volumes of 3681–4530 litres, so 1kg into the air vents would average out to about 250 g / m3, which is a 150000% increased risk of cardiopulmonary mortality.

What did Bliss Air not tell us? Timescale. Is that constant exposure over a decade, over one year or over a week or just half an hour twice a day for five days a week? Also, how soon is this heart attack likely to happen?
Oh, Willie McBride, it was all done in vain.

Eebster the Great
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### Re: Science-based what-if questions

Sableagle wrote:E = mc2 conversion? So for 10 kJ I'd need a 10000 / c2 kg black hole?

A 111.265 pg black hole. Umm ... around a billion atoms?

There are also clearly theoretical challenges with the notion of such a small black hole. Black holes are sometimes seen as having a minimum mass of about the Planck mass, or 20 micrograms.

Sableagle
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### Re: Science-based what-if questions

Well, I thought there'd have to be a minimum mass and it'd be greater than that of one iridium nucleus ... but 20 µg is quite a lot. 1797510357 J, or 429615 g TNT. Half a tonne, near enough. How convenient that such bombs have been made. We can *see* what it'd do!

That's not something you want to bring to a knife fight, is it?
Oh, Willie McBride, it was all done in vain.

Tub
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### Re: Science-based what-if questions

There are several lower bounds for black hole size. The uncertainty principle says that you cannot confine mass in an arbitrarily small volume, so any black hole's size (schwarzschild radius) cannot be smaller than the planck length (which is tiny), but such a black hole would have a mass of planck mass, which is surprisingly heavy for planck units.

We also don't know how space behaves around the planck scale, which is the whole problem with quantum gravity. Assuming that space is smooth enough to to form an event horizon around planck scale is.. speculative.

Wikipedia lists another lower bound of 1016 kg for any black hole containing Fermions. Unless I fumbled my units, that's roughtly the mass of hong kong and all the non-molten rock below it, compressed into a volume slightly smaller than a hydrogen atom. If such a black hole were to instantly evaporate into radiation, that would be equivalent to 100 earth-sized balls of TNT going off.

Letting a 10 year old boy control such powers seems unwise.

p1t1o
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### Re: Science-based what-if questions

Sableagle wrote:
That's not something you want to bring to a knife fight, is it?

Only if you love LOSING

gmalivuk
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### Re: Science-based what-if questions

Tub wrote:If such a black hole were to instantly evaporate into radiation, that would be equivalent to 100 earth-sized balls of TNT going off.

"Fortunately", such a black hole would actually take 2.7e24 years to evaporate.
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Zamfir
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### Re: Science-based what-if questions

US Midsize cars have internal volumes of 3681–4530 litres, so 1kg into the air vents would average out to about 250 g / m3, which is a 150000% increased risk of cardiopulmonary mortality.

The numbers are for PM2.5, particles with a hydraulic diameter below 2.5 micrometer. Your small glitter is 200 micrometer, so that's about a million times larger in mass terms. In health terms, they are completely different things. On a per-kg basis, fine particles are way, way more damaging than large particles. They stay airborne and they penetrate deep into the lungs.

Sableagle
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### Re: Science-based what-if questions

Fine, fine.

Five litres of stale cat urine, then.
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Tub
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### Re: Science-based what-if questions

gmalivuk wrote:
Tub wrote:If such a black hole were to instantly evaporate into radiation, that would be equivalent to 100 earth-sized balls of TNT going off.

"Fortunately", such a black hole would actually take 2.7e24 years to evaporate.

True if gradual evaporation via hawking radiation is the only relevant effect. But, assuming there is a lower limit for black hole size, then surely something else must happen once the black hole shrinks below that size. I have no idea what that could be, but one way or another it has to stop being a black hole at that point.

Eebster the Great
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### Re: Science-based what-if questions

Tub wrote:
gmalivuk wrote:
Tub wrote:If such a black hole were to instantly evaporate into radiation, that would be equivalent to 100 earth-sized balls of TNT going off.

"Fortunately", such a black hole would actually take 2.7e24 years to evaporate.

True if gradual evaporation via hawking radiation is the only relevant effect. But, assuming there is a lower limit for black hole size, then surely something else must happen once the black hole shrinks below that size. I have no idea what that could be, but one way or another it has to stop being a black hole at that point.

You are misunderstanding the scale. The minimal black hole has a mass of 2.2 × 10−8 kg and a radius of 1.6 × 10−35 m. Such a black hole, if it can evaporate at all, should do so almost instantly, on a time scale comparable to the Planck time of 5.4 × 10−44 s, releasing radiation with an energy of the Planck energy 2.0 × 109 J, or less than half a ton TNT equivalent.

The black hole gmalivuk is talking about that takes quadrillions of eons to evaporate is the one you took from Wikipedia at 1016 kg. That is 24 orders of magnitude more massive than the Planck mass, like the comparison of the mass of the Earth to the mass of a cat. While this microscopic black hole would be rather hot (12 million K), it would still take forever to radiate away so much mass.

gmalivuk
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### Re: Science-based what-if questions

Tub's point was that if that's actually the minimum mass a black hole can exist at (not just form, but remain), then it couldn't still be a black hole smaller than that. Whether that means it would suddenly explode and release all its energy at once, or whether it just means that there'd no longer be an event horizon and it'd just be a tiny amount of extremely dense matter, is unclear.
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andykhang
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### Gravity chain reaction

Since it's all about black hole recently, let keep up the streak.

So,IIRC, gravitational wave directly expand and contract the space itself, and the matter within it. So, theoratically, you could directly used the gravitational wave itself to compress thing into ridiculous density, and possibly into a black hole.

Assuming I want to turn every single star in the Milky Way Galaxy into a black hole, even for a brief moment, by having 2 astronomical scale black hole in a orbit that would result in them colliding at the center of the universe. At what size would it be enough to do that?

Eebster the Great
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### Re: Science-based what-if questions

Without doing any calculations, probably more massive than the observable universe. Gravitational waves result from a changing quadrupole moment in the gravitational field. Circular orbits have constant zero quadrupole moments, so they do not produce gravitational waves. And the waves produced by elliptical or decaying orbits are extraordinarily small except near a merger. To collapse red dwarfs into black holes would require a strain of something like 250,000. Over a distance of tens of kiloparsecs.

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### Re: Science-based what-if questions

From a Because science video: 9mm bullet hits man's skin at 350 m/s. Fails to penetrate even the thickness of a human hair (0.05mm). Kyle seemed to pull that number and "in 1 millisecond" out of his armpit at that point. I make it just over 4c/s that the bullet has to be accelerated backwards to stop it in that distance.

I'm pretty sure something ought to break down if you try to stop a bullet that hard, but what?

Would the bullet just splash?
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Eebster the Great
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### Re: Science-based what-if questions

You can find the magnitude of acceleration with Torricelli's equation, which does not include time as a variable:
a = (vf2 - vi2)/(2 ∆x)
Where a is the magnitude of average acceleration, vi is the initial speed (350 m/s), vf is the final speed (0 m/s), and ∆x is the magnitude of displacement (0.05 mm = 5 × 10-5 m). That gives a = 1.22 × 109 m/s2 = 4.09 c/s if c is the speed of light in a vacuum, as you surmised. The time can be calculated using the definition of average acceleration (a = ∆v/∆t) or any other equation of motion. In particular, using only three givens (with no intermediate calculations), you can use the property that if acceleration is constant, average velocity is the arithmetic mean of initial and final velocity ∆x/∆t = (vi+vf)/2. Solving for time gives ∆t = 285 ns = 2.85 × 10-4 ms, so "less than a millisecond" is a vast understatement. Bullets go kind of a long way in a millisecond, especially compared to a hair's breath.

This acceleration is about 120 million gees, which is about 300 times the surface gravity of a white dwarf or about 0.0002 times the surface gravity of a neutron star.

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### Re: Science-based what-if questions

Sableagle wrote:
Would the bullet just splash?

Well i mean that is a video of a bullet doing exactly that...

In ballistics, this is called "Interface Defeat" - where the difference in strengths/hardness overcomes the relationship between velocity, mass and impact depth.

Very high accelerations can be observed, 120million gees is not completely ridiculous. The acceleration of a 9mm round in a 10cm barrel is on the order of 440,000gees and that is over a much larger distance than would be travelled in an interface defeat. It wouldnt blow my mind if the 120millionG figure actually happens under some circumstances.
Just not with human skin, what was that garbage about?

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### Re: Science-based what-if questions

Luke Cage.

He is bulletproof, for some reason. Judging by the sound-effects, bullets bounced rather than splashing.

It's very silly. Because Science did a thing about it and someone was questioning his maths, so I checked out the maths too and ... like I said, Kyle pulled those numbers out of his armpit.
Oh, Willie McBride, it was all done in vain.

Sableagle
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### Re: Science-based what-if questions

Eebster the Great wrote:You can find the magnitude of acceleration with Torricelli's equation, which does not include time as a variable:
a = (vf2 - vi2)/(2 ∆x)
Where a is the magnitude of average acceleration, vi is the initial speed (350 m/s), vf is the final speed (0 m/s), and ∆x is the magnitude of displacement (0.05 mm = 5 × 10-5 m). That gives a = 1.22 × 109 m/s2 = 4.09 c/s if c is the speed of light in a vacuum, as you surmised. The time can be calculated using the definition of average acceleration (a = ∆v/∆t) or any other equation of motion. In particular, using only three givens (with no intermediate calculations), you can use the property that if acceleration is constant, average velocity is the arithmetic mean of initial and final velocity ∆x/∆t = (vi+vf)/2. Solving for time gives ∆t = 285 ns = 2.85 × 10-4 ms, so "less than a millisecond" is a vast understatement. Bullets go kind of a long way in a millisecond, especially compared to a hair's breath.

This acceleration is about 120 million gees, which is about 300 times the surface gravity of a white dwarf or about 0.0002 times the surface gravity of a neutron star.

Thanks.

I just worked something else out: if that bullet stops then its energy pretty much goes into heat, and it can't dissipate much heat in that tiny time interval, so it's going to get almost 500°C hotter.
Oh, Willie McBride, it was all done in vain.

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### Re: Science-based what-if questions

Sableagle wrote:Luke Cage.

He is bulletproof, for some reason. Judging by the sound-effects, bullets bounced rather than splashing.

It's very silly. Because Science did a thing about it and someone was questioning his maths, so I checked out the maths too and ... like I said, Kyle pulled those numbers out of his armpit.

Oooooh its a sci-fi thing, ok.

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### Re: Science-based what-if questions

Who was that on Wolverine's mercenary squad in X-Men Origins: Wolverine (IIRC) who stuck his arm down a tank/artillery muzzle to prevent it firing (successfully!)? Ah, nevermind, I think I recall that that was The Blob, in his svelte pre-('Bub'/)Blob days. But must have similar dissipative abilities (even before the weight gain).