快猫短视频

UH-OH, the mad scientists are at it again. In their determination to extract
nature鈥檚 secrets, physicists in America have built a machine so powerful it has
raised fears that it might cause The End of The World As We Know It.

鈥淏ig Bang machine could destroy Earth鈥� ran the headline over a story in
The Sunday Times last month. It claimed that our planet was in peril from a
vast new American particle accelerator on Long Island, the Relativistic Heavy
Ion Collider (RHIC), which will collide pairs of gold nuclei at high energies.
According to the article, RHIC could trigger a catastrophic event: the creation
of a black hole or a ravenous 鈥渟trangelet鈥� that could swallow up our entire
planet.

Within 24 hours, the laboratory issued a rebuttal: the risk of such a
catastrophe was essentially zero. The Brookhaven National Laboratory that runs
the collider had set up an international committee of experts to check out this
terrifying possibility. But BNL director John Marburger, insisted that the risks
had already been worked out. He formed the committee simply to say why they are
so confident the Earth is safe, and put their arguments on the Web to be read by
a relieved public.

Even so, many people will be stunned to learn that physicists felt worried
enough even to mull over the possibility that a new machine might destroy us
all.

In fact, they鈥檝e been fretting about it for over 50 years. The first
physicist to get the collywobbles was Edward Teller, the father of the hydrogen
bomb. In July 1942, he was one of a small group of theorists invited to a secret
meeting at the University of California, Berkeley, to sketch out the design of a
practical atomic bomb. Teller, who was studying the reactions that take place in
a nuclear explosion, stunned his colleagues by suggesting that the colossal
temperatures generated might ignite the Earth鈥檚 atmosphere.

While some of his colleagues immediately dismissed the threat as nonsense, J.
Robert Oppenheimer, director of the Manhattan Project, set up to build the atom
bomb, took it seriously enough to demand a study. The report, codenamed LA-602,
was made public only in February 1973. It concentrated on the only plausible
reaction for destroying the Earth, fusion between nuclei of nitrogen-14. The
report confirmed what the sceptics had insisted all along: the nuclear fireball
cools down too far quickly to trigger a self-sustaining fire in the
atmosphere.

Yet in November 1975, The Bulletin of the Atomic 快猫短视频s claimed
that Arthur Compton, a leading member of the Manhattan Project, had said that
there really was a risk of igniting the atmosphere. It turned out to be a case
of Chinese whispers: Compton had mentioned the calculation during an interview
with the American writer Pearl Buck, who had got the wrong end of the stick.

Even so, the Los Alamos study is a watershed in the history of science, for
it marks the first time scientists took seriously the risk that they might
accidentally blow us all up. The issue keeps raising its ugly head.

In recent years the main focus of fear has been the giant machines used by
particle physicists. Could the violent collisions inside such a machine create
something nasty? 鈥淓very time a new machine has been built at CERN,鈥� says
physicist Alvaro de Rujula, 鈥渢he question has been posed and faced.鈥�

One of the most nightmarish scenarios is destruction by black hole. Black
holes are bottomless pits with an insatiable appetite for anything and
everything. If a tiny black hole popped into existence in RHIC, the story goes,
it would burrow down from Long Island to the centre of the Earth and eat our
planet鈥攐r blow it apart with all the energy released. So why are
physicists convinced that there鈥檚 no chance of this happening?

Well, the smallest possible black hole is around 10^-35 metres across (the
so-called Planck Length). Anything smaller just gets wiped out by the quantum
fluctuations in space-time around it. But even such a tiny black hole would
weigh around 10 micrograms鈥攁bout the same as a speck of dust. To create
objects with so much mass by collisions in a particle accelerator demands
energies of 10¹⁹ giga-electronvolts, so the most powerful existing collider is
ten million billion times too feeble to make a black hole. Scaling up today鈥檚
technology, we would need an accelerator as big as the Galaxy to do it.

And even then, the resulting black hole wouldn鈥檛 be big enough to swallow the
Earth. Such a tiny black hole would evaporate in 10^-42 seconds in a blast of
Hawking radiation, a process discovered by Stephen Hawking in the 1970s. To last
long enough even to begin sucking in matter rather than going off pop, a black
hole would have to be many orders of magnitude bigger. According to Cliff
Pickover, author of Black Holes: A Traveler鈥檚 Guide, 鈥淓ven a black hole
with the mass of Mount Everest would have a radius of only about 10^-15 metres,
roughly the size of an atomic nucleus. Current thinking is that it would be hard
for such a black hole to swallow anything at all鈥攅ven consuming a proton
or neutron would be difficult.鈥�

So we needn鈥檛 lose sleep about creating an Earth-eating black hole in an
accelerator. But according to John Wheeler of Princeton University, there is
another way: detonating a big hydrogen bomb. He showed that the pressures
generated by a suitable explosion could crush matter to the densities needed
(around 10¹⁷ kilograms per cubic metre) to stand a chance of creating a black
hole. However, Wheeler estimated that a 鈥渟uitable鈥� H-bomb would require all the
heavy water in the oceans, and weigh many billions of tonnes. Some bomb.

The more discerning mad scientist might instead opt to pick a black hole 鈥渙ff
the shelf鈥�. One left over from the Big Bang or an exploding star, for example.
The temptation is certainly there, for as the Oxford mathematician Roger Penrose
showed 30 years ago, black holes make wonderfully clean sources of energy. Just
throw a skipful of junk at a black hole in the right way, Penrose discovered,
and it will eat up all the junk and then hurl the empty skip back out again with
more energy than it had before.

Fortunately, there鈥檚 not much chance of bringing a black hole to Earth any
time soon. After all, they would be rather unwieldy and the nearest one is
likely to be many light years away.

It was while dismissing the black-hole threat in last month鈥檚 Scientific
American that theorist Frank Wilczek of the Institute for Advanced Study in
Princeton mentioned an altogether more exotic form of killer blob:
鈥渟迟谤补苍驳别濒别迟蝉鈥�.

Strangelets are chunks of matter made from 鈥渟trange鈥� quarks as well as the
usual 鈥渦p鈥� and 鈥渄own鈥� types of ordinary matter. It might be possible to make
them in particle accelerators like RHIC. The risk is that a strangelet might
consume nuclei of ordinary matter and convert them into more strange matter,
transmuting the entire Earth into a strange-matter planet. But having raised
this appalling prospect, Wilczek quickly dismissed it.

And quite rightly, says the world鈥檚 leading expert on strangelets, Robert
Jaffe of the Massachusetts Institute of Technology. 鈥淪trangelets are almost
certainly not stable, and if they are, they almost certainly cannot be produced
at RHIC,鈥� he says. 鈥淎nd even if they were produced at RHIC, they almost
certainly have positive charge and would be screened from further interactions
by a surrounding cloud of electrons.鈥� Every one of these steps in the argument
would have to be flawed for strangelets to be a risk.

Blown to smithereens

But don鈥檛 heave a sigh of relief just yet. The Brookhaven scientists have
also considered an even more alarming possibility than the destruction of the
Earth. Could their mighty machine trigger the collapse of the quantum
vacuum?

Quantum theory predicts that the Universe is filled with a seething melee of
so-called vacuum energy. That might seem an unlikely threat to civilisation.
After all, it鈥檚 simply the average energy of the mess of particles that flit in
and out of existence all around us. As the Universe expanded and cooled, that
vacuum energy dropped down to the lowest possible level.

Or did it? What if the Universe is still 鈥渉ung up鈥� in an unstable state? Then
a jolt of the right amount of energy in a small space might trigger the collapse
of the quantum vacuum state. A wave of destruction would travel outwards at the
speed of light, altering the Universe in bizarre ways. It would be rather bad
news for us, at least: ordinary matter would cease to exist.

In 1995, Paul Dixon, a psychologist at the University of Hawaii, picketed
Fermilab in Illinois because he feared that its Tevatron collider might trigger
a quantum vacuum collapse. Then again in 1998, on a late night talk radio show,
he warned that the collider could 鈥渂low the Universe to smithereens鈥�.

But particle physicists have this covered. In 1983, Martin Rees of Cambridge
University and Piet Hut of the Institute of Advanced Study, Princeton, pointed
out that cosmic rays (high-energy charged particles such as protons) have been
smashing into things in our cosmos for aeons. Many of these collisions release
energies hundreds of millions of times higher than anything RHIC can
muster鈥攁nd yet no disastrous vacuum collapse has occurred. The Universe is
still here.

This argument also squashes any fears about black holes or strange matter. If
it were possible for an accelerator to create such a doomsday object, a cosmic
ray would have done so long ago. 鈥淲e are very grateful for cosmic rays,鈥� says
Jaffe.

But RIHC is special, goes the counter-argument, because it collides gold
nuclei together. What if some subtle unforeseen physical effect makes collisions
between heavy nuclei particularly dangerous? Fortunately, there are some heavy
nuclei among the multitude of cosmic rays that fly through the Solar System. 鈥淲e
believe there are relevant cosmic ray 鈥渆xperiments鈥� for every known threat,鈥�
says Jaffe. 鈥淓ven if one insists on gold-gold collisions, there have been enough
such collisions on the surface of the Moon since its formation 5 billion years
ago to assure us that RHIC experiments are safe.鈥�

So until we can build atom smashers so powerful that they can exceed the
energy of the punchiest cosmic rays, we needn鈥檛 lose any sleep over them.
Paranoiacs should look elsewhere, and a good place to start would be in the
pages of journals like Physical Review Letters, which have carried
schemes for extracting energy from the quantum vacuum. The worry here is that
no-one knows how much energy might be unleashed: calculations give answers
anywhere between zero and infinity. Arthur C. Clarke once raised the possibility
that some of those vast explosions we see in the cosmos may be smart-alec alien
scientists getting their comeuppance for tinkering with the quantum vacuum:
鈥渢hey might be industrial accidents鈥� he said.

Those of a nervous disposition should stop reading now. For some top
physicists are toying with the idea of recreating the birth of the Universe
right here on Earth (see 鈥淐osmos-making for amateurs鈥�). One of the big names
backing this idea is cosmologist Andrei Linde of Stanford University. He admits
that he has no idea how to trigger a little big bang, yet insists that the
experiment would not be catastrophic.

But then, as the Russian theorist Lev Landau once said: 鈥淐osmologists are
often wrong, but never in doubt.鈥� Perhaps Linde鈥檚 reassurance will turn out to
be the very last Famous Last Words.

快猫短视频s are often accused of trying to play God. But obviously they can鈥檛
really mimic the feats of the putative Creator of the Universe, and make a
universe in the laboratory. Or can they?

Before you snort in disbelief, you should know that some serious cosmologists
have considered the idea. Indeed, one of them has already had a shot at creating
a universe鈥攁lbeit inside a computer.

The idea dates back to the late 1970s, when Andrei Linde, now at Stanford
University, and Alan Guth of the Massachusetts Institute of Technology
separately came up with the concept of 鈥渋nflation鈥�. According to this idea, an
incredibly short, violent burst of expansion occurred around 10^-32 seconds
after the birth of the Universe. Propelled by concentrated vacuum energy,
inflation boosted the size of the Universe from one billionth the width of a
proton to the size of a grapefruit.

That鈥檚 what the theorists claim, but showing that inflation really did take
place like this is hard鈥� unless, of course, someone can recreate the right
conditions in the lab and watch what happens. Linde and his colleagues have
already done a dry run on a computer. 鈥淪etting up the simulations was hard work,
and only on the seventh day did we finish the first series,鈥� he reported in
Scientific American in 1994, adding in Strangelovian terms: 鈥淲e looked at
the shining screen, and we were happy鈥攚e saw that the universe was
驳辞辞诲!鈥�

This isn鈥檛 enough for Linde: he wants to do it for real. But theory suggests
that matter has to be squeezed to densities similar to those in the primordial
Universe before such fields appear. No-one has the faintest clue how to create
such densities, yet.

Linde is sanguine about the dangers involved, if it ever becomes possible.
鈥淵ou can think of our Universe as being like a smooth surface, with one part of
it inflating like a balloon. The new universe will be connected to ours by just
a tiny passage鈥攚hat we call a wormhole鈥攖he size of a subatomic
particle.鈥� Quite how we鈥檇 know we鈥檇 succeeded isn鈥檛 obvious, but at least there
seems little danger of someone tumbling into the new universe by mistake, or
anything nasty getting out.