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The practical case for manned spacef light gets ever-weaker with each advance in robots and miniaturisation - indeed, as a scientist or practical man, I see little purpose in sending people into space at all. But as a human being, I'm an enthusiast for manned missions.
There's no doubt that the Moon is more than a handy night light and a hair restorer for werewolves. It's responsible for the substantial amplitude of earthly ocean tides. These are of obvious influence if you're a geoduck, a type of clam that people dig up at low tide.
We have this interesting problem with black holes. What is a black hole? It is a region of space where you have mass that's confined to zero volume, which means that the density is infinitely large, which means we have no way of describing, really, what a black hole is!
The Universe forces those who live in it to understand it. Those creatures who find everyday experience a muddled jumble of events with no predictability, no regularity, are in grave peril. The Universe belongs to those who, at least to some degree, have figured it out.
Stars that become supernovae start off at least eight times heavier than our sun. They're so short-lived that, even if they have planets, there is unlikely to be time for life to get started. The surface is 40,000C and, as a result, the colouring will be extremely blue.
The chief contribution of such a radically new and more powerful instrument would be, not to supplement our present ideas of the universe we live in, but rather to uncover new phenomena not yet imagined, and perhaps modify profoundly our basic concepts of space and time.
Astronautics, strictly speaking, will be concerned with voyages to other stars. Remarkably enough, to achieve such feats, we might not even have to leave the earth. It would suffice to accelerate the sun itself to a very high speed and let it drag all its planets with it.
We're interested in things that have big teeth, and you can see the evolutionary value of that, and you can also see the practical consequences by watching 'Animal Planet.' You notice they make very few programs about gerbils. It's mostly about things that have big teeth.
I think there's a lot of intelligence out there, but that's just my guess. Question is: Are they peaceable or hostile? You could say that the peaceable ones are just going to stay at home and play with their Nintendos, so if you do meet any of them, they might be hostile.
One hardly knows where, in the history of science, to look for an important movement that had its effective start in so pure and simple an accident as that which led to the building of the great Washington telescope, and went on to the discovery of the satellites of Mars.
I'm interested in finding whether or not there is a really massive, what we like to call 'super massive' black hole at the center of our galaxy. And the reason this is interesting is that it gives us an opportunity to prove whether or not these exotic objects really exist.
The Platonists and their Christian successors held the peculiar notion that the Earth was tainted and somehow nasty, while the heavens were perfect and divine. The fundamental idea that the Earth is a planet, that we are citizens of the Universe, was rejected and forgotten.
If we ever established contact with intelligent life on another world, there would be barriers to communication. First, they would be many light years away, so signals would take many years to reach them: there would be no scope for quick repartee. There might be an IQ gap.
The stars look the same from night to night. Nebulae and galaxies are dully immutable, maintaining the same overall appearance for thousands or millions of years. Indeed, only the sun, moon and planets - together with the occasional comet, asteroid or meteor - seem dynamic.
Are two eyes, four appendages and an upright posture really essential for any creature that can ace the galactic SAT's? Maybe not. In fact, I'd venture that any aliens we ever detect or (less likely) encounter will look quite different than this self-referential stereotype.
Consider: Life arose on Earth close to four billion years ago. Four billion years of slithering, swimming, and soaring life forms. But only in the last 200 thousand years has a species arisen that can fathom the laws of nature and build hardware able to signal its presence.
The key to proving that there's a black hole is showing that there's a tremendous amount of mass in a very small volume. And you can do that with the motions of stars. The way the star moves around the center of the galaxy is very much like the way the planets orbit the sun.
Who is more humble? The scientist who looks at the universe with an open mind and accepts whatever the universe has to teach us, or somebody who says everything in this book must be considered the literal truth and never mind the fallibility of all the human beings involved?
Many people suggest using mathematics to talk to the aliens, and Dutch computer scientist Alexander Ollongren has developed an entire language (Lincos) based on this idea. But my personal opinion is that mathematics may be a hard way to describe ideas like love or democracy.
'Battleship' is not a film that Francois Truffaut would have made. Nor would any of those other namby-pamby European directors. Nope, this picture eschews that Continental obsession with small stories, set in quaint towns filled with pockmarked folk doing their banal things.
It is emphatically the case that life could not arise spontaneously in a primeval soup of any kind.... Furthermore, no geological evidence indicates an organic soup ever existed on this planet. We may therefore with fairness call this scenario the myth of the pre-biotic soup.
All the atoms we are made of are forged from hydrogen in stars that died and exploded before our solar system formed. So if you are romantic, you can say we are literally stardust. If you are less romantic, you can say we're the nuclear waste from fuel that makes stars shine.
The mission of NASA's Kepler telescope is to lift the scales from our eyes and reveal to us just how typical our home world is. Kepler operates by measuring the dimming of stars as planets pass ('transit') in front of them. It has found thousands of previously unknown worlds.
Consider that the overwhelming majority of those 40,000 near-Earth asteroids are small enough to fit on the parking lot at the mall. And while these rocky runts won't cause Armageddon, they could still flatten such popular hominid hangouts as Manhattan or downtown Des Moines.
Heads are a good deal, and I think they would be a common feature. It's hard to think of species that don't have heads, although there are some. It's good to have a head because it puts some of the sensory organs - eyes, ears, whiskers or whatever - next to the CPU, the brain.
How do you observe something you can't see? This is the basic question of somebody who's interested in finding and studying black holes. Because black holes are objects whose pull of gravity is so intense that nothing can escape it, not even light, so you can't see it directly.
In our interconnected world, novel technology could empower just one fanatic, or some weirdo with a mindset of those who now design computer viruses, to trigger some kind of disaster. Indeed, catastrophe could arise simply from technical misadventure - error rather than terror.
In the case of climate change, the threat is long-term and diffuse and requires broad international action for the benefit of people decades in the future. And in politics, the urgent always trumps the important, and that is what makes it a very difficult and challenging issue.
It would be sad if the expertise built up during the 40 years of the U.S. and Russian manned programmes were allowed to dissipate. But abandoning the shuttle, and committing to new launch vehicles and propulsion systems, is actually a prerequisite for a vibrant manned programme.
The most attractive habitats for synthetic sentience might be the vicinities of exceptional sources of energy - for example black holes, or even the neighbourhoods of large stars, which routinely boil off the energy of ten thousand suns. These are the destinations they may seek.
You're an interesting species, an interesting mix. You're capable of such beautiful dreams and such horrible nightmares. You feel so lost, so cut off, so alone, only you're not. See, in all our searching, the only thing we've found that makes the emptiness bearable is each other.
There are many instances in science, where those closest to the intricacies of the subject have a more highly developed sense of its intractability than those at some remove. On the other hand, those at too great a distance may, I am well aware, mistake ignorance for perspective.
'By convention there is color, by convention sweetness, by convention bitterness, but in reality there are atoms and the void,' announced Democritus. The universe consists only of atoms and the void; all else is opinion and illusion. If the soul exists, it also consists of atoms.
The fact that we can't easily foresee clues that would betray an intelligence a million millennia farther down the road suggests that we're like ants trying to discover humans. Ask yourself: Would ants ever recognize houses, cars, or fire hydrants as the work of advanced biology?
Any beings advanced enough to traverse interstellar distances are at least a thousand years beyond our technical level. Spending gobs of time examining our missiles is equivalent to sending the Air Force back to the Middle Ages and insisting they examine the chain mail factories.
When was the last time you bought an American-made radio or television? If you're Gen X or younger, the answer is 'never.' Does the label on that shirt or skirt you're wearing say 'Made in the U.S.A.'? If so, you probably got it at Goodwill, or maybe at a Smithsonian garage sale.
The Cosmos is all that is or was or ever will be. Our feeblest contemplations of the Cosmos stir us -- there is a tingling in the spine, a catch in the voice, a faint sensation, as if a distant memory, of falling from a height. We know we are approaching the greatest of mysteries.
Indeed the reasoned criticism of a prevailing belief is a service to the proponents of that belief; if they are incapable of defending it, they are well advised to abandon it. This self-questioning and error-correcting aspect of the scientific method is its most striking property.
Issues relating to global health and sustainability must stay high on the agenda if we are to cope with an ageing and ever-increasing population, with growing pressure on resources, and with rising global temperatures. The risks and dangers need to be assessed and then confronted.
The scientific issues that engage people most are the truly fundamental ones: is the universe infinite? Is life just a sideshow in the cosmos? What happened before the Big Bang? Everyone is flummoxed by such questions, so there is, in a sense, no gulf between experts and the rest.
Perhaps future space probes will be plastered in commercial logos, just as Formula One cars are now. Perhaps Robot Wars in space will be a lucrative spectator sport. If humans venture back to the moon, and even beyond, they may carry commercial insignia rather than national flags.
What's a space elevator? Simply described, it's a thin ribbon, about 3 feet wide and 60 thousand miles long, stretching upwards from the surface of the Earth. The lower end is bolted to a heavy anchor (think of an oil drilling platform), and the top is capped with a counterweight.
The neurochemistry of the brain is astonishingly busy, the circuitry of a machine more wonderful than any devised by humans. But there is no evidence that its functioning is due to anything more than the 10(14) neural connections that build an elegant architecture of consciousness.
Ocean planets might be very common in the universe because water is very common in the low-temperature environments where planets form and evolve. This might be especially true for super-Earths, which can retain volatiles more easily thanks to their larger mass and surface gravity.
It is a mistake to imagine that potentially great men are rare. It is the conditions that permit the promise of greatness to be fulfilled that are rare. What is so difficult to achieve is the cultural background that permits potential greatness to be converted into actual greatness.
I recall a lecture by John Glenn, the first American to go into orbit. When asked what went through his mind while he was crouched in the rocket nose-cone, awaiting blast-off, he replied, "I was thinking that the rocket has 20,000 components, and each was made by the lowest bidder."
Space doesn't offer an escape from Earth's problems. And even with nuclear fuel, the transit time to nearby stars exceeds a human lifetime. Interstellar travel is therefore, in my view, an enterprise for post-humans, evolved from our species not via natural selection, but by design.
Equipped with our five senses - along with telescopes and microscopes and mass spectrometers and seismographs and magnetometers and particle accelerators and detectors sensitive to the entire electromagnetic spectrum - we explore the universe around us and call the adventure science.
If you could drive straight down, into a tunnel bored through the crust of the planet, you'd hit this molten mess in about an hour. It's called the asthenosphere - a sluggish sea, several hundred miles thick, on which floats the Earth's cool epidermis - the so-called tectonic plates.
After I give lectures-on almost any subject-I am often asked, "Do you believe in UFOs?" I'm always struck by how the question is phrased, the suggestion that this is a matter of belief and not evidence. I'm almost never asked, "How good is the evidence that UFOs are alien spaceships?"