Q: What are “actual pictures” of atoms actually pictures of?

Something IBM made with some very flat, very clean, very cold copper and a few hundred carbon monoxide molecules.

Something IBM made with some very flat, very clean, very cold copper and a few hundred carbon monoxide molecules.

Physicist: Actual pictures of atoms aren’t actually pictures at all.

There are a few good rules of thumb in physics.  Among the best is: light acts like you’d expect on scales well above its wavelength and acts weird on scales below.  In order to take a picture of a thing you need light to bounce off of it in a reasonable way and travel in straight lines (basically: behave like you’d expect).  But the wavelength of visible light is about half a micrometer (a two-millionth of a meter) and atoms are around one ångström (a ten-billionth of a meter) across.  On the scale of atoms, visible light acts too wonky to be used for photographs.

Atoms are literally too small to see.

An actual photograph of a billiard ball (#3) and what we have in lieu of a photograph of an atom.

(Left) A photograph of a 3 ball.  (Right) What we have in lieu of a photograph of an atom.

You could try using light with a shorter wavelength, but there are issues with that as well.  When light has a wavelength much shorter than an atom is wide, it takes the form of gamma rays and each photon packs enough energy to send atoms flying and/or strip them of their electrons (it is this characteristic that makes gamma rays dangerous).  Using light to image atoms is like trying to get a good look at a bird’s nest by bouncing cannonballs off it.

There are “cheats” that allow us to use light to see the tiny.  When the scales are so small that light behaves more like a wave than a particle, then we just use its wave properties (what else can you do?).  If you get a heck of a lot of identical copies of a thing and arrange them into some kind of repeating structure, then the structure as a whole will have a very particular way of interacting with waves.  Carefully prepared light waves that pass through these regular structures create predictable interference patterns that can be projected onto a screen.  Using this technique we learned a lot about DNA and crystals and all kinds of stuff.  This is the closest thing to a photograph of an atom that is possible using light and, it’s fair to say, it’s not really what anyone means by “photograph”.  It’s less what-the-thing-looks-like and more blurry-rorschach-that-is-useful-to-scientists.  Even worse, it’s not really a picture of actual individual atoms, it’s information about a repeating structure of atoms that happens to take the form of an image.


By passing light (left) or even electron streams (right) through a regular, crystalline structure we create an interference pattern that gives us information about the structure of the crystal (but never pictures of individual atoms).  The picture on the left (left) is a pattern created by DNA (species unimportant).  Notice how not obvious the helical structure is.  The picture on the right is created by an electron beam passing through some simple mineral or salt.

These techniques are still in use today (are relatively cheap), but since 1981 we’ve also had access to the Scanning Tunneling Electron Microscope (STM).  However, despite the images it creates, the STM isn’t taking a photograph either.  The STM sees the world the way a blind person on the end of a tiny robotic arm sees the world.

The essential philosophy behind the Scanning Tunneling Electron Microscope is what allows this dude to know more about the bottom of this chili cauldron than you do.

The STM is basically a needle with a point that is a single atom (literally, it is the pointiest thing possible) which it uses to measure subtle electrical variations (such as a stray atom sitting on what was otherwise a very flat, clean surface).  The “Tunneling Electron” bit of the name refers to the nature of the electrical interaction being used to detect the presence of atoms; when the tip is brought close to an atom electrons will quantum tunnel between them and the exchange of electrons is a detectable as a current.  The “Scanning” bit of the name refers to how this is used to generate a picture: by scanning back and forth across a surface over and over until you’ve bumped every atom with your needle several times.  The pictures so generated aren’t photographs, they’re maps of what the STM’s needle experienced as it was moved over the surface.  The STM “sees” atoms using this needle in the same way you can “see” the bottom of a muddy river with a pokin’ stick.

An STM and some of the pictures it "paints".

An STM and some of the pictures it pokes into being.

This technology has been around for decades and, like the advent of the synth, has given rise to all manner of jackassery.

Posted in -- By the Physicist, Physics, Quantum Theory | 4 Comments

Q: If you were shrunk to microscopic size would you be able to see normally? Would you be able to see microscopic things?

The original question was: In the ‘60s sci-fi classic “Fantastic Voyage,” the crew of a submarine crew are shrunk to microscopic size and injected into the body of an injured scientist.  I realize that this film is rather sloppy from a scientific point of view, but here’s my question:  The shrunken crew members are able to see microscopic objects, like white blood cells.  But, assuming you could scale a person down, does having smaller eyes necessarily mean you can see smaller – even microscopic — objects?  I can’t make out one-point type, even if it is printed clearly through some high-resolution photographic process.  Would I be able to if I were the size of an ant?  Would scaling down our eyes give them the same capabilities as a microscope?

The Fantastic Voyage, 1966.

The Fantastic Voyage, 1966.

Physicist: Yes and no, but mostly no.  This question basically boils down to: if you were scaled down so that tiny things were large compared to you, would they appear large to your now-tiny eyeballs, with all of their microscopic details made macro?

If you were shrunk down until a blue

If you were shrunk down until a Lego brick appeared as large as this sound stage at Estudios Churubusco, then would it literally look like this to your tiny eyes?

The answer is yes: as lenses and eyeballs shrink, the world literally does look bigger.  But mostly no: the smaller you get, the darker the world will appear and if you’re shrunk to less than about one 10,000th of your size, the lenses in your eyes will cease to work on visible light.

A smaller lens with the same shape and material will focus light at a proportionately shorter distance.

A smaller lens made in the same shape and with the same material will focus light at a proportionately shorter distance.  This means that your eyes should continue to work normally; things that are now relatively larger, will appear larger.

The way light interacts with a lens is dictated by the material and the geometry of the lens.  Assuming your tiny eyes are the same shape and material as your present eyes (and they always appear to be in the movies), they should work normally.  If there’s a cell or Lego brick in front of you and about your size, it will appear to be about your size.  You should be able to see smaller details as though the tiny object were literally larger just by walking up to it.

There is an issue.  The amount of light bouncing off of tiny things, or flying into tiny eyes, is small.  So tiny eyes are always in the dark.  Overcoming this problem is why fancy microscopes have light bulbs.  Assuming that you, the things you’re interacting with, and the distance to the things you’re interacting with, are all scaled down by the same factor, x (e.g., you’re shrunk and injected into the bloodstream of Dr. Benes), then everything around you will appear to be darker by the inverse square of this factor, x-2.  Everything around you would appear to be x times bigger, but the lights would all be x-2 times dimmer.

Smaller eyes mean less light. By the time you're the size of a cell, the amount of light needed for a human eye to see would set you on fire.

Smaller eyes collect less light. By the time you’re the size of a cell, the amount of light needed for a human eye to see is more than enough to set you on fire.

So if you’re shrunk from being a couple meters tall to being a couple millimeters tall (shrunk by a factor of 103), then the tiny world around you would appear one millionth as bright (decreased by a factor of 10-6).  The noon-day Sun would appear about as bright as a full Moon to the milli-you.

In the Fantastic Voyage the ship is shrunk to one micrometer across; a factor of around ten million, 107.  The ambient light would need to be one hundred trillion times brighter in order for their environment to have appeared normally lit.  If you tried this, you’d see just fine for the fractions of a second before you were cooked.  1014 is a big factor.

Even worse, there’s a diffraction limit brought about by the wave nature of light.  Below scales about as large as its wavelength, light starts to act more wavy and less particly.  It oozes around corners and ripples around obstacles.  In a micro-meter eyeball visible light cannot be relied upon to propagate in a straight line; instead it would splash haphazardly onto your retina.  As you shrink through the diffraction limit (assuming there was still enough light to see) the world would get blurrier until it just “blurred out” entirely.  Visible light has a wavelength of about half a micrometer and our pupils are around 2 – 5 mm across; about ten thousand times bigger.  So, if you were shrunk by a factor of around ten thousand, then you’re eyes will no longer be able to focus incoming light and project it into useful images.  You’d basically be in a haze of the average light coming from every direction.

Left: Laser light going through a wide aperture. Right: laser light going through a very small aperture.

Left: Laser light through a wide aperture. Right: laser light through a very small aperture.  The scattering effect of diffraction prevents micrometer scale (or smaller) eyes from being able to form images.

White blood cells are about 10 μm across, or about 20 visible-light-wavelengths.  The diffraction limit would start to be an issue when they appear to be about the size of golfballs, and you’d be completely blind when the white blood cells appeared to be about the size of your head.

Despite the difficulties, micrometer sized eyes do exist.  But because of the difficulties, they’re crap.  Fortunately, the smallest eyes belong to (technically “are”) single celled critters, which are universally too dumb to notice the quality.  Synechocystis is cyanobacterium (uses photosynthesis for energy) that’s about 3 micrometers across and uses its entire body as an eyeball.  Light passing through the cell focuses a little more in the surface of the cell opposite from the light’s source.  This isn’t a trick that’s difficult to evolve; it’s something raindrops do just as well en route to the ground.  What makes Synechocystis an “eye” is the fact that it then reacts to that “image”.  By swimming away from the bright spot it swims toward the Sun (or any other bright source of light), which is a good move for a critter that eats light.  Because of the diffraction limit, this sloppy slightly-brighter-region is about the only image that the tiniest possible eyeball can create and we shouldn’t expect to find eyes much smaller.

A whole tiny world of Mr. Magoo's walking toward the light.

Synechocystis: the smallest, or very nearly the smallest, eyes possible.

Posted in -- By the Physicist, Biology, Physics | 7 Comments

Q: How does one attain an understanding of everything?

Metatem, High Chair of Truscience: The true path to enlightenment, born of the enlightenment, is obviously Truscience.  Truscience replaces the “old science”, which is full of complicated symbols that no one understands, crazy stories about ancient lizard monsters killed by a giant rock, and the laziest creation myth ever conceived: a “Big Bang”.  St. Bertrand forgive the fools!  It is common knowledge that if you can’t explain an idea to a 5-year-old, then you don’t understand it.  Clearly “scientists” don’t understand much of anything.  All of Truscience is, of course, completely backed up by modern scientific knowledge only without any of the wrong stuff (hence the name).

Truscience combines the true findings of the old science with modern quantum meditation.  Finally free of the shackles of “math” we can come to understand reality through the lens of the Truself.  It took trillions of years of old science for humanity to finally realize that it doesn’t take trillions of years of science to fully comprehend the manyverse.  To know the full scope of time and space we need only ask Laplace’s Demon.

The great Knower.

The High Chancellor communing with followers of Truscience from other planets, post-singularity energy matrices, and the future.

I can’t underscore this enough: science is hard.  It takes decades of meditation, logic, and introspection to be granted total knowledge and at all times you’ll be assailed from all sides by the Unreasoning masses who have been fooled into believing that mathematics and expensive equipment are the path to knowledge.  Fortunately, you don’t have to understand Truscience to completely believe it.  In fact, striving to understand every little thing really gets in the way.  All you need is faith.  Faith and a nominal fee to participate in a few classes, workshops, and friendly, purifying get-togethers.

We (the followers of Truscience) have come a long way from our cargo-cult origins.  Whereas we once only went through the motions of science without a spiritual connection, now we have access to the manyversal truths.  For example, we now know that we will all live forever.  As St. Newton divined, “energy is neither created nor destroyed” and as St. Einstien proved “energy and matter are the same thing”.  Therefore, once our matter-bodies release our energy-selves each be sorted by Maxwell’s Demon; some will ascend into the Singularity and some will be left behind to be crushed under our robot feet.

We also now know that whatever we believe is true.  As St. Shrodinger showed when he killed a cat with his mind, quantum physics means that we can make of reality whatever we truly wish.  It wasn’t until after I earned all my degrees and found my true name, Metatem, that I came to understand Truscience.  Now that I’m 7th degree, it’s my turn be in the High Chair.

According to our most basic precepts, all people are followers of Truscience (zeroth degree) except of course for “the Unreasoning”; which includes such poisonous influences as concerned family members and old-science “scientists” who dispute the truth of Truscience.  The power of Truscience is that it’s true whether you believe it or not, because we believe it (and thus it is manifestly so).  And we should know.  The followers of Truscience are smarter than followers of every other religion and creed for a simple reason: the Aumann Agreement theorem, which says that all smart people will eventually agree.  Therefore all smart people either believe in Truscience, haven’t heard of it, or have been compromised by an Unreasoning.

Truly, how can something with so much science and smart, moral people not be true?

Posted in -- Guest Author, April Fools | 5 Comments

Q: Can planes (sheets) be tied in knots in higher dimensions the way lines (strings) can be tied in knots in 3 dimensions?

Physicist: Yes!

And just to be clear, we're not talking about this. This is cheating.

Just to be clear, we’re not talking about this. This is cheating.

Mathematicians are pretty good at talking about things in spaces with any number of dimensions.  Sometimes that math is fairly easy and even intuitive.  For example, a line has 2 sides (ends), a square has 4 sides, a cube has 6 sides, and a hypercube has __* sides.

Ordinary knots (that you can tie with string) can only exist in exactly 3 dimensions.  It’s impossible to create a knot in 2D since every knot involves some amount of “over-and-under-ing” and in 2D space there’s none of that.  Because it makes the math more robust, mathematicians always talk about knots being tied in closed loops rather than on a bight.  In part because once you’ve connected the ends of your string the knot you’ve got is the knot you’ve got, and that invariance is very attractive to math folk.

In order to tie even the simplest knot (left) you need to

Left: In two dimensions, no matter how complicated and convoluted your string is it can never be tied in a knot.   Right: Even the simplest knot requires at least three over-under excursions into three dimensional space to get around self-intersections.

In 2D, if you have a dot inside of a circle, it’s stuck.  But if you have access to another dimension (“dimension” basically means “direction”), then you can get the dot out.  In exactly the same way, if you can “lift” part of a regular knot into a fourth dimension it’s like opening the loop and you’re free to untie your knot in the same way you’d untangle/untie anything.  Afterwards you just “lower” the segment of the string back so that it all sits in 3D and now you’ve just got a loop of unknotted string (very creatively, this is called an “unknot”).  So, you’ve managed to untied your knot without worrying about self-intersections and all it took was an extra dimension.

In 2D a dot can be stuck inside of a circle, but if we have the option to "lift"

In 2D a dot can be stuck inside of a circle, but if we have the option to “lift” part of the circle in a new direction then the dot can get out.  From the perspective of the flat denizens of 2D space, this looks like part of the circle being removed.

All that was just to say: be excited, the way you tie your shoes is only possible in universes similar to (with the same number of dimensions as) our own.  You can’t tie a knot in a string in two dimensions and a knotted string in four (or more) isn’t really knotted at all.

The way we talk about ordinary knots is in the context of a loop (tie your knot and then splice the loose ends of the string).  The generalization of a loop (a 1-sphere) to higher dimensions is first the surface of a regular sphere (a 2-sphere), then the surface of a hyper-sphere (a 3-sphere) and so on.  An N-sphere can be tied in a knot in N+2 dimensional space.

An N-sphere can be tied in knots in N+2 dimensions. 1-spheres can be tied in knots in three dimensions (they're call)

An N-sphere can be tied in knots in N+2 dimensions. 1-spheres can be tied in knots in three dimensions (these are known colloquially as “knots”), which means that they can actually be created.  2-spheres (the surface of a ball) can be tied in knots in four dimensions.  The image here is only a cross-section of such a knot.

It turns out that if you have an ordinary knot, you can use it to create a higher dimensional knot.  There are a several ways to do this.  There’s “suspension“, which usually doesn’t work (the created knot is often not a “manifold“, which is kinda cheating), and there’s also “spinning” which always works.

The basic idea behind spun knots. As the line moves it sweeps out a surface.

The basic idea behind spun knots.

To create a “spun knot” you rotate it in a higher dimensional space and collect all of the points that it sweeps through.  The picture above is more symbolic than applicable.  In this picture a knot in 3D is spun to create a sphere that’s still in 3D space, but with a funky-shaped tube running around its equator.  That’s not a knot (knot at all).  This process needs to be done in four dimensions, where the added direction allows you to get around the self-intersection problem, but the basic idea is the same.  So for every knot that you can tie with a loop of rope in 3D, there’s a knot you can tie with a hollow sphere in 4D.

And yes: you can keep going into higher and higher dimensions using the same idea.

While you can’t directly picture a four dimensional knot, you can create cross-sections (the same way a 2-dimensional being might picture 3-dimensional objects using cross-sections).  This video (~0.4MB) shows 3D cross-sections of a rotating 4D knot.  But be warned: that video is, for lack of a better word, groovy.

Sometimes a group of scientists will get really involved with a particular subject and kinda disappear up their collective butts for a while (especially mathematicians).  Eventually one of them will emerge like a prairie dog and bark “fellow dudes and dudesses, we should really send a message to the world so they don’t worry about us” at which point a summarizing paper such as this or this is written (about higher dimensional knots in this case), in an attempt to convey to a slightly broader audience what they’ve been doing.

And now to justify our existence!

Mathematicians after a long think.

The tied sheets painting is by Teun Hocks and is from here.

The 4D knot picture and the video are from here.

The spun knot picture was lifted remorselessly from the second paper mentioned earlier.


Posted in -- By the Physicist, Geometry, Math | 8 Comments

Gravity Waves!

Physicist: A few days ago we managed to detect gravity waves for the first time.  Gravity waves were predicted a century ago by Einstein as a consequence of his general theory of relativity.  This success isn’t too surprising from a theoretical stand point; if
your theories are already batting a thousand, then when they bowl yet another field
goal for a check mate no one is shocked.

What is amazing is not that gravity waves exist, but that we’ve managed to detect
them.  The effect is so unimaginably small that it can be overwhelmed by someone
stubbing their toe a mile away or filing their taxes wrong.  Gravity is literally
the geometry of spacetime: very particular, tiny increases and decreases in
distances and durations.  There’s a fairly standard technique for doing this: light
is bounced back and forth along two separate paths between mirrors (in this case the
length of those two paths are each 4km) dozens of times.  The light from these two
paths is then brought together and allowed to interfere.  If the difference in the
length of the two paths changes by half a wave length, then instead of destructive
interference we see constructive interference.  The actual path difference is
substantially less than half a wave length, but it’s still detectable.

LIGO is b

A gravity wave detector is a device that very, very carefully measures the difference between the lengths of two long paths.  (Left) The tiny difference is detected by looking at the interference between lasers that travel along each path.  (Right) What the detector in Livingston, LA looks like from above.

When a gravity wave ripples through the Earth, the lengths of the two paths change
by about one part in 1021 which is a tiny fraction of the width of a proton over 4 km.  Keep in mind that the light that’s doing the measuring is bouncing off of mirrors that are made of atoms (each of which is much bigger than a proton) and that those atoms are constantly jiggling, because that’s what any level of heat does to matter.  This level of precision is the most impressive part of this whole accomplishment.  Your heart beat is currently throwing around the building you’re in by a lot more than a proton’s width.  And yet, despite the fact that the literally everything in the world is a source of experiment-ruining noise, LIGO is able to filter all of it out and then go on to detect the ridiculously faint signal of a couple of black holes a fair fraction of the universe away and even sort out details of the event.

The signal that we’re hearing about now was actually detected in September.  The cause appears to be the merging of two black holes about 1.3 billion lightyears away (which puts the source well outside of our backyard).  These black holes started with masses of around 36 and 29 times the mass of the Sun and after combining left a black hole with a combined mass of about 62 Sun-masses.  Astute second graders will observe that 36+29>62.  This is because gravity waves carry energy.  In this case the final event turned about 3 Sun’s worth of energy into ripples in spacetime that are “loud” enough to literally (albeit very, very slightly) rattle everything in the universe.  So, if we ever contact aliens from the other side of the universe and they also have nerds, then we’ll have something to talk about.  By the way, this signal (unlike so many in physics) has a frequency well within the range of human hearing.  Properly cleaned up, it sounds like this.

(Top) The signal as detected at the two observatories. The noise is bad enough that without at least two observatories it would be much more difficult to see it. (Middle) The signal as predicted by our understanding of general relativity. (Bottom) The remaining noise after the signal has been subtracted. Notice that it is now fairly constant. (Picture on the bottom) This is a plot of the strength of the signal using color vs. frequency on the vertical axis and time on the horizontal axis.

(Top) The signal as detected at the two observatories. The noise is bad enough that without at least two observatories it would be much more difficult to see it.
(Middle) The signal as predicted by our understanding of general relativity. (Bottom) The remaining noise after the signal has been subtracted. Notice that it is now fairly constant.
(Picture on the bottom) This is a plot of the strength of the signal using color vs. frequency on the vertical axis and time on the horizontal axis.

This is the first direct measurement of gravity waves, but it isn’t the first evidence we’ve seen.  If you have two really heavy masses in orbit around each other, you’ll find that they’ll slowly spiral together.  This is strange because it implies that the masses are losing energy.  But to what?  We first measured this effect with pulsars, which are a kind of neutron star (the next densest things after black holes).  Pulsars are so named because they produce radio pulses that are extremely regular.  You can think of them as giant space clocks.  They’re precise enough that they allow us to figure out exactly how they’re moving using doppler shifts, and they’ve shown that closely orbiting pairs lose energy in exactly the way we’d expect based on our theoretical understanding of gravity waves.

So what can we use this for?  So far we’ve been able to “hear” black holes merging (several more times since September).  We’re not only detecting the spiraling in, but also the process of the black holes coalescing.  Once they come in contact they briefly form an unshelled-peanut-shaped black hole before assuming a spherical shape.  This process is called the “ring down” and it also creates audible gravity waves that give us information about the behavior of black holes.  But beyond heavy things in tight orbits and ringing black holes, what will we hear?  Short answer: who knows.  If you go out in the woods you’ll hear trees falling over when no one is around and lots of bears shitting, but there’s no telling what else you’ll hear.  The only way to find out is to go out and listen.  As our gravity wave detectors get better and more plentiful we’ll be able to hear fainter and fainter signals.  We can expect to hear lots of black holes merging; not because it’s common, but because it’s loud and the universe is big.  Soon we’ll start hearing things we don’t expect and that’s when the science happens.  It’s nice to have our theories regarding gravity waves proven right, but being right isn’t the point of science.  As long as you’re right, you’re not learning.  It’s all the things we don’t expect that will be the most exciting.

Gravity wave astronomy is only the third way we have of observing the distant universe: light, neutrinos, and now gravity waves.  We didn’t know what we’d find with the first two and it’s fair to say we don’t know what we’ll learn now.  Exciting times.

You can read the paper that announced the achievement here.  And check out the author list: there was more collaboration on this than a Wu Tang album.

Update (6/20/2016): And again!

Posted in -- By the Physicist, Experiments, Physics | 10 Comments

Q: Is it possible to parachute to Earth from orbit?

Physicist: Yes and no, but mostly no.

It’s certainly possible to parachute safely to Earth from the top (or nearly the top) of the atmosphere, but this question isn’t about parachuting from space it’s about parachuting from orbit.  An orbit isn’t just a matter of being very high, it’s mostly a matter of being very, very fast.

Newton tried to explain orbits in terms of a progressively more and more powerful cannon.

Newton tried to explain orbits in terms of a progressively more and more powerful cannon.

When you throw something it follows a curved path that eventually intersects the surface of the Earth (technically this is already an orbit, it just gets interrupted by stuff in the way).  If you use a cannon, then the curve straightens out a bit but it still intersects the surface of the Earth, just farther away.  With a really, really powerful cannon (or more likely: a rocket) you can get something moving so fast that the curve of its fall matches the curve of the Earth.  When this happens the object is in orbit; a closed loop around the Earth that repeats forever.

You may have noticed that the Earth isn’t terribly curved, so it may seem that you’d need to be moving impossibly fast to follow it.  That’s exactly the case: above the air but near the surface of the Earth you’d need to be moving sideways at about 8km/s.  This is more than 23 times faster than the speed of sound.  Not slow.

A) An astronaut in low Earth orbit, who will stay there.
B) A stationary astronaut at the same height, who will be on the ground (impact on the ground) in half an hour or so.

This 8 km/s speed corresponds to the slowest, lowest orbit.  Any other orbit either won’t bring you close to the atmosphere or will do so faster (at up to about 11 km/s).  Being the slowest and lowest, these roughly circular “near Earth orbits” are very popular (that is to say: cheap).  Near Earth orbit is probably what you’re imagining when you think of parachuting to the Earth.

Orbits at different heights. In low Earth orbit are the International Space Station, the Hubble space telescope, and most communication satellites.

Orbits at different heights. In low Earth orbit are the International Space Station, the Hubble space telescope, and most communication satellites.

So here comes the point.  You can go as fast as you want if you’re doing it in space, but when you’re measuring your speed in km per second, air starts to feel like concrete (hot concrete).

The effects of air on something designed to handle it. A bag of meat (a person) would fare worse.

The effect of air on a “heat shield” designed to handle it (the bottom of the Apollo 11 crew capsule).  A bag of meat (like a person in a spacesuit) would fare worse.

When an object plows through air at very high speeds it tends to burn, shatter, and shred.  Parachutes are used for most entries and reentries, but not initially; most of the deceleration from orbit is handled by heat shields, which are a cross between parachutes and bricks (or a brick and another kind of brick).  Once enough of a falling object’s speed has been shed by a heat shield (typically slower than sound, but up to a few times faster), it is then safe to deploy an actual parachute.

If you were to jump (fast) out of the International Space Station with the aim of entering the atmosphere and deploying your chute, you’d find it filled in short order then torn to ribbons shortly after.  Like any falling star, you’d find yourself hot, dead, and profoundly luminous.  Like icy meteors, you’d probably flash into steam and air burst before reaching the ground.

The reason you can’t parachute from orbit is simply a matter of engineering.  We haven’t yet created parachutes that can survive being deployed, and then work properly, at speeds above around mach 2.  At reentry speeds, which are in excess of mach 23, parachutes just can’t hold up.  However, someday it may be possible.  We know that the accelerations involved are survivable, and there don’t seem to be any fundamental limitations, we just need better materials and techniques.  Also, for at least a little while, a spacesuit capable of reentry on its own (before the parachute has had a change to slow it) would be nice.

Merely falling from space is probably pretty easy.  The highest jump so far was from 24 miles up.  A jump from space is a mere four times higher.  You’d need a rocket instead of a balloon, but aside from being a silly thing to do, there’s nothing stopping someone from doing it.

Posted in -- By the Physicist, Engineering, Physics | 8 Comments