For Plato, the world of appearance was a kind of dream, and the real world was something that only the initiated could begin to understand through logic and mathematics, and perhaps a dash of magic. So far as it existed, matter was evil, and the universe was strictly bounded in space and time.
For Epicurus, the world of appearance was the real world. There is a void, or vacuum, which is infinite in space and time. It has always existed. It will always exist. It goes on forever and ever. In this void is an infinite number of atoms. These are very small, and therefore imperceptible, but indivisible particles of matter. They have always existed and will always exist. They are all moving through the void at an incredibly rapid and uniform speed. The world as we see it is based on combinations of these atoms. Every atom is hooked, and the collision of atoms will sometimes lead to combinations of atoms into larger structures, some of which endure and some of which we can eventually perceive with our senses. All observed changes in the world are the result of redistributions of the invisible atoms that comprise it.
Though we are not able to see these atoms, we can infer their existence by looking at the world that our senses can perceive. All events — the wearing away of a rock by water, for example, or the growth of crystals or trees — can be fully explained by an atomic hypothesis. Since there is nothing that cannot be so explained, there is no need of any other hypotheses. In a surviving explanation of his method, he says:
…[I]n our study of nature we must not conform to empty assumptions and arbitrary laws, but follow the prompting of the facts.
Everything in the universe is made of atoms. We are made of atoms. Our souls are made of very fine atoms. Our senses work because every other physical object is continually casting off very thin films of atoms that represent it exactly as it is. These films strike on our senses and give us vision and sound. Heat is produced by the vibration of atoms temporarily trapped in structures that prevent them from their natural onward motion.
Whether or not anyone can at any moment think of a likely explanation, all events in the universe can be explained in purely naturalistic terms. Assuming atoms and motion, no further hypotheses are needed to explain the world.
Epicurus was not the first to explain the world by an atomic hypothesis. That was Democritus (460-370 BC). But he seems to have developed the hypothesis with a consistency and detail that took it far beyond anything that earlier philosophers had conceived.
Perhaps his most notable innovation is the doctrine of the swerve. There are two objections to the atomism of Democritus. The first is that if the atoms are all moving at the same speed and in the same direction, like drops of rain, there is no reason to suppose they will ever collide and form larger compounds. The second is that if they are not moving in the same direction, they will collide, but they will form a universe locked into an unbreakable sequence of cause and effect. This conflicts with the observed fact of free will.
And so Epicurus argues that every atom is capable of a very small and random deviation from its straight motion. This is enough to give an indeterminacy to the universe that does not conflict with an overall regularity of action.
Sean Gabb, “Epicurus: Father of the Englightenment”, speaking to the 6/20 Club in London, 2007-09-06.
September 7, 2016
QotD: Plato, Epicurus and Democritus
December 9, 2015
SF “war in space” memes of improbability
Charles Stross explains several SF novel shibboleths that make him want to hurl the book against the nearest wall, including so many “war in space” stories:
Newton’s Second Law, for dummies. E = 1/2 * (mv2) — it’s not just a good idea, it’s the law. Notice the huge distances I alluded to above? Well, to get between planet A and planet B in anything approximating reasonable human time spans, you need to go fast. And if you go fast, your velocity relative to the bodies around you is also high. In event of an inelastic collision the kinetic energy transfer is proportional to the square of your velocity; and this has drastic consequences for space ships. Suppose you’re in low Earth orbit and you hit a piece of space junk, for example a screw that’s fallen off someone else’s ship. It’s traveling in pretty much the same orbit as you, but inclined at 30 degrees. What happens? What happens is you get a happy fun experience much like being hit by a bullet from a high-calibre sniper’s rifle, because (I can’t be bothered to do the trig here) it’s packing a velocity component angled across your path at a goodly fraction of orbital velocity, and at orbital velocity a kilogram of water packs kinetic energy equal to about ten times its mass in exploding TNT.
You know what a high-speed car crash looks like, right? Space ships travel a lot faster than that: if they hit something, it’s going to be very messy indeed. And that’s at sluggish orbital velocities; if you starship is barreling along at about 85% of the speed of light general relativity has something to say on the subject and it’s kinetic energy is equal to about half it’s rest mass — the equivalent of a 10 megaton hydrogen bomb for every kilogram of hull weight. (The pilot’s space-suited body alone packs the energetic punch of a Peak Strangelove 1980s USA/USSR strategic nuclear exchange.)
Human bodies are basically squishy sacks of goopy grease and water emulsions held together by hydrogen bonds and disulphide bridges between protein molecules and glommed onto some big lumps of high-grade chalk. We evolved in a forgiving, water-dominated low-velocity world where evolution didn’t bequeath us nervous systems able to comprehend and deal with high energy interactions other than in an “ooh, that lightning bolt was close! Where’s cousin Ugg?” kind of way. We can’t even see objects that flash across our visual field in less than 50 milliseconds — a duration in which, at orbital velocity, an object will have travelled on the order of half a kilometer.
Intuition and high energy regimes: do the math, or your space combat will be a whole bundle of nope.
(Other related cognitive errors include but are not limited to: Napoleonic navies clashing in space and firing broadsides back and forth at one another’s line of battle … spaceships with continuous high acceleration fusion-powered motors or similar that don’t glow white-hot then melt because vacuum is an insulator and shedding that much heat is a hard engineering problem (hint: a 100 ton spaceship accelerating at 1g requires 1 megaJoule of thrust: using a photon rocket for maximum efficiency that’s going to require 3 x 1015 watts of juice going in, if it’s 99.9% effective at heat dissipation that means it’s racking up around three terawatt of leakage, and that’s equivalent to about 45 kilotons of nuclear explosions per minute of waste heat) … warships using active radar to hunt for one another (hint: active sensor reach is inversely proportional to the fourth power of the emission strength, passive sensors obey the inverse square law) … warships using stealth in space (hint: infrared emissions, second hint: the background temperature you want to avoid standing out against is 2.73 degrees Kelvin, i.e. liquid Helium temperature) …
Oh for fuck’s sake, don’t get me started on war in space, we’ll be here forever unless we just throw physics to the winds of fiction and delegate all our hand-waving to magic hyperspace or cyberspace technology or something.
March 31, 2011
“Free neutrons don’t beam, homie”
The ever-informative wormme has another good post up, this one is about misunderestimating neutrons:
We can’t say for sure TEPCO was monitoring for neutrons there — they’ve made some pretty big mistakes so far — but they’d be hard to miss. All those emergency responders sprawled lifelessly on the ground would have been a clue. From that absolute godawfully unimaginable flux of ground-zero neutrons, doncha know. Because despite “reporting” like this:
…observed a neutron beam…(snip snip)…when a beam of neutrons…
Free neutrons don’t beam, homie. (emphasis added, obviously) Apart from neutrinos and anti-neutrinos, nothing’s harder to beam than neutrons. They like to spread, not bunch. (Okay, Leopold, maybe muons and the like are worse.)
A neutron walks into a bar and says, “how much for a drink?”. Bartender says, “for you…no charge.” The neutron beamed…
October 9, 2010
“Global warming is the greatest and most successful pseudoscientific fraud I have seen in my long life”
James Delingpole posts the most interesting resignation letter you’re likely to see this year:
Harold Lewis is Emeritus Professor of Physics at the University of California, Santa Barbara. Here is his letter of resignation to Curtis G. Callan Jr, Princeton University, President of the American Physical Society.
Anthony Watts describes it thus:
This is an important moment in science history. I would describe it as a letter on the scale of Martin Luther, nailing his 95 theses to the Wittenburg church door. It is worthy of repeating this letter in entirety on every blog that discusses science.
It’s so utterly damning that I’m going to run it in full without further comment.
August 31, 2010
Do we live in a “basement” universe?
Many years back, one of the mailing lists I regularly read had a long and interesting discussion about the possibilities of creating new universes. Not in a science-fictional sense, but based on the theories then current and using the technologies which were already under development at the time. They were referred to as “basement universes”, “pocket universes” and so on. It was fascinating, although my weak math abilities forced me to skip over the parts of the discussion with all the numbers and symbols.
Elizabeth sent me a link to John Gribbin’s “Are we living in a designer universe?”, which took me back to those fascinating discussions:
The argument over whether the universe has a creator, and who that might be, is among the oldest in human history. But amid the raging arguments between believers and sceptics, one possibility has been almost ignored — the idea that the universe around us was created by people very much like ourselves, using devices not too dissimilar to those available to scientists today.
As with much else in modern physics, the idea involves particle acceleration, the kind of thing that goes on in the Large Hadron Collider in Switzerland. Before the LHC began operating, a few alarmists worried that it might create a black hole which would destroy the world. That was never on the cards: although it is just possible that the device could generate an artificial black hole, it would be too small to swallow an atom, let alone the Earth.
However, to create a new universe would require a machine only slightly more powerful than the LHC — and there is every chance that our own universe may have been manufactured in this way.
August 7, 2010
Bereaved Ohio family suing Norfolk Southern for failing to change laws of motion
Sorry for their loss, but suing the railroad because the train crew didn’t change the laws of physics to avoid hitting Matthew Johnson as he ran along a trestle won’t work:
The family of a man who was hit by a train while jumping off a trestle into a river two years ago is suing the railroad and a local canoe center, according to documents filed in Clark County Common Pleas Court Thursday, Aug. 5.
Matthew Johnson, 21, died Aug. 10, 2008 while he and three other people were standing on a train trestle between Old Mill Road and the Masonic Temple grounds.
Johnson’s mother, Carol Johnson, of West Carrollton, has filed suit against Norfolk Southern Railway Company and Aaron’s Canoe and Kayak Center, Springfield.[. . .]
Among the allegations listed in the complaint:
• The canoe company “knew or should have known that individuals frequently went onto the train trestle and jumped into the Mad River.”
• Train conductors “failed to timely and effectively stop the train,” causing Johnson’s death.
• The railroad was negligent in its duty to “maintain and equip its train with all necessary navigational and/or safety devices.”
Just so we’re clear here: there is no “navigational and/or safety device” ever conceived that can safely stop a multi-thousand ton freight train in less than hundreds of metres of distance. Physics does not play favourites — once that much mass is in motion, it takes a lot of energy to stop it without catastrophic dis-assembly.
