Steemit.chat is dead. Being forced to socialize with my people I was asked the question that titles this article. A rather strange question that I was never asked before
The thing is, he also added that neither the method or shape of the substance matter. It can be a venom, poison, explosive... Whatever I want.
The topic of the question resides in "quantity"
Having nothing better to do, since the chatroom is dead (yes, again), I decide to write the answer by beginning with the poisons.
Any substance can kill us if we expose to a large quantity of it. As a matter of fact, things that we ingest on a daily basis are potentially poisonous if we consider that.
"All things are poison, and nothing is without poison, the dosage alone makes it so a thing is not a poison." -Paracelsus.
To evaluate toxicity the la median lethal dose (LD50) is used, this is the mass of a substance that is needed to kill 50% of the people exposed to it.
Take, water, for example. It IS toxic in large quantities: Its LD50 is around 90 ml per kilogram of body mass (of the person that ingests it, of course). This means that somebody that weights 70 kg, like me, would have 50% of dying by drinking 6.3 liters of water over a short period of time.
Dehydration is bad, over-hydration... worse.
Of course that 6.3 liters of water is a rather large amount of matter, and would not fit as a potential answer to that question. There's plenty of things around us that would kill us with much less effort, like: sugar.
It has an LD50 of 29.7 g/kg, I would have to eat a bit over 2 kg of sugar to put my life at risk. That's roughly around 3.5 kg (7.7 pounds) of Nutella, in case you're wondering.
Table salt has a ten times higher toxicity with 3 g/kg. 249 grams (0.55 pounds) of salt in my salad to have a 50/50 chance of surviving.
Those are things we normally ingest, lets get off the chart a bit
450 mg/kg is lead's magic number, this is 31.5 g would compromise my well being. This is... if I ingested it. If I shot a 22 cal bullet with a rifle to my head, the dose would be lower, and not have that 50% bonus!
Now, this looks good! Speed makes things become lethal!
The most toxic substance known until today is the "Botulinum Toxin", it is produced by a bacteria called "Clostridium Botulinum". Its intravenous LD50 is around 1.3 to 2.1 nanograms/kg of body mass (1 nanogram is one thousand-millionth of a gram). So, I'd need around 91 to 149 ng of it injected to reach the danger zone. Now, let me warn you: Buying Botulinum Toxin (BOTOX, for short) can be quite expensive at today's rates.
Therefore, this is the poison that may kill a person with the smallest amount of substance. Yet, not only poisons can kill us!
Time to go into sci-fi mode!
Antimatter, how much do we need to kill me? We can produce it in particle accelerators. Extremelly small quantities of it and we have no clear understanding on how to contain it yet (The last record I've heard of was of 17 minutes).
This is a nice candidate, sin when it contacts normal matter both annihilate each other releasing all their masses in the shape of energy (100%). Contrasting it with things we may see everyday: The nuclear fission process like the one on bombs or in stars only converts 0.7% of the mass into energy... You can see how much can that small percentage can do.
A single gram of antimatter interacting with matter would have as much energy as 43 million kilograms of TNT. How much mass of antimatter is needed to vanquish me?
To be safe, lets suppose that someone attempted to bomb me in an "allahu akhbar" style. Then, 100 g of TNT would be needed (to be sure that I don't come back). those 100 grams would be equal to 2.33 nanograms of antimatter. Comparing that mass to the Botulinum Toxin: Antimatter wins!
Yet, it may not be cost efficient: 58 million USD to produce those 2.33 ng!
I hate when I start thinking, then I just cannot stop!
My next idea would be heading right into subatomic particles, radiation.
Anywhere you go, your body is bombarded by really tiny projectiles.
When these particles collide against our cells, they may destroy part of their DNA and create errors in the genetic code. You know... Cancer.
I would say that this is the smallest amount of mass needed to kill a man. A single subatomic particle triggering Cancer in the worst possible place.