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1. The energy source needed to
create and maintain the galactic jet in galaxy PKS 0521-36 is
generated deep within the core of the galaxy, and is far too small
to resolved. The favored mechanism behind these cosmic fireworks
is a spinning, massive black hole. The hole is fueled by a
continual in-fall of nearby gas and stars. This gravitational
accretion process is far more efficient at converting mass to
energy than thermonuclear fusion processes which power individual
stars. The extraordinary high pressure and temperature generated
near the hole would cause some of the in-falling gas to be ejected
along the direction of the black hole's spinning axis to create
the galactic jet.
2. NASA's Hubble Space Telescope has uncovered the strongest
evidence yet that many stars form planetary systems. Hubble
discovered extended disks of dust around 15 newly formed stars in
the Orion Nebula, a starbirth region 1,500 light-years away. Such
disks are a prerequisite for the formation of solar Systems like
our own.
3. This is a Hubble Space Telescope image (right) of a vast nebula
NGC 604 in the Triangulum galaxy M33. This is a site where new
stars are being born in a spiral arm of the galaxy. Though such
nebulae are common in galaxies, this one is particularly large,
nearly 1,500 light-years across. The nebula is so vast it is
easily seen in ground-based telescopic images (left). At the heart
of NGC 604 are over 200 hot stars, much more massive than our Sun
(15 to 60 solar masses). They heat the gaseous walls of the nebula
making the gas flouresce. Their light also highlights the nebula's
three-dimensional shape, like a lantern in a cavern. By studying
the physical structure of a giant nebula, astronomers may
determine how clusters of massive stars affect the evolution of
the interstellar medium of the galaxy. The nebula also yields
clues to its star formation history and will improve understanding
of the starburst process when a galaxy undergoes a "firestorm" of
star formation.
4. This spectacular color panorama of the center of the Orion
Nebula is one of the largest pictures ever assembled from
individual images taken with the Hubble telescope
1. What makes the Universe tick?
We have reached the point where we can't go any further with many
of the other really interesting phenomena and questions in physics
until this problem is solved. To understand topics such as
the topics such as the origin of the Universe, the ultimate fate
of black holes and the possibility of time travel, we need to
understand how the Universe works.
We now have a good idea what the basic building blocks of matter
might be. Physics in the 20th century was built on the twin
revolutions of quantum mechanics (a theory of matter) and
Einstein's theory of space, time and gravitation known as
relativity. But it's extremely unsatisfying to find two
ultimate descriptions of reality when you are looking for just
one.
Trying to unify the two theories presents formidable technical and
conceptual obstacles that have challenged some of the finest
theoretical physicists for decades. For example, because
gravitation manifests itself as a warping of a four-dimensional
environment called space-time, applying quantum theory to gravity
causes problems. For one thing, it means bringing
Heisenberg's uncertainty principle to bear on space-time itself,
which is decidedly problematic.
But may be that means there's a problem with this approach:
perhaps we shouldn't be trying to quantise gravity alone.
Most recent attempts at unification subsume the problem of
quantizing gravity into a broader approach that aims to bring all
the forces of nature, as well as all subatomic particles, into one
theoretical framework. This is the idea that some physicists
call a "theory of everything".
One current approach is superstring theory, which posits tiny
loops of string (rather than point-like particles) as the basis of
all matter. Another approach, M theory, is still more
abstract and can be pictured as membranes moving in higher space
dimensions. But perhaps the level of progress in these ideas
is best summed up by the fact that no one quite remembers what the
"M" in M theory is supposed to stand for. There's a long
road ahead.
1. This Hubble telescope picture of
the Egg Nebula, also known as CRL2688, shows a pair of mysterious
"searchlight" beams emerging from a hidden star and criss-crossed
by numerous bright arcs. This image sheds new light on the poorly
understood ejection of stellar matter that accompanies the slow
death of Sun-like stars. The nebula is really a large cloud of
dust and gas ejected by the star, expanding at a speed of 115,000
mph (20 km/s).
2. This Hubble telescope snapshot of MyCn18, a young planetary
nebula, reveals that the object has an hourglass shape with an
intricate pattern of "etchings" in its walls. A planetary nebula
is the glowing relic of a dying, Sun-like star. The results are of
great interest because they shed new light on the poorly
understood ejection of stellar matter that accompanies the slow
death of Sun-like stars. According to one theory on the formation
of planetary nebulae, the hourglass shape is produced by the
expansion of a fast stellar wind within a slowly expanding cloud,
which is denser near its equator than near its poles
3. The end of a Sun-like star's life was once thought to be
simple: the star gracefully casts off a shell of glowing gas and
then settles into a long retirement as a burned-out white dwarf.
Now, a dazzling collection of detailed views from the Hubble
telescope reveals surprisingly intricate, glowing patterns spun
into space by aging stars: pinwheels, lawn sprinkler-style jets,
elegant goblet shapes, and even some that look like a rocket
engine's exhaust. In this picture of M2-9, twin lobes of material
emanate from a central, dying star. Astronomers have dubbed this
object the "Twin Jet Nebula" because of the shape of the lobes. If
the nebula is sliced across the star, each side appears much like
a pair of exhausts from jet engines. Indeed, because of the
nebula's shape and the measured velocity of the gas, in excess of
200 miles per second, astronomers believe that the description as
a super-super-sonic jet exhaust is quite apt.
4. Astronomers using the Hubble telescope have obtained the
sharpest view yet of a glowing loop of gas called the Ring Nebula
(M57), first cataloged more than 200 years ago by French
astronomer Charles Messier. The pictures reveal that the "Ring" is
actually a cylinder of gas seen almost end-on. Such elongated
shapes are common among other planetary nebulae, because thick
disks of gas and dust form a waist around a dying star. This
"waist" slows down the expansion of material ejected by the doomed
object. The easiest escape route for this cast-off material is
above and below the star. This photo reveals dark, elongated
clumps of material embedded in the gas at the edge of the nebula;
the dying central star is floating in a blue haze of hot gas.
2. What's the universe made of?
"Ordinary atoms of the sort we are made
of represent a tiny impurity in a universe dominated by Something
Else?"
Alas, the embarrassment continues. Physicists don't know for
sure what's out there. In astronomy, what you see isn't what
you get: stars, planets, gas and dust consist of normal atoms, but
for every gram of ordinary stuff in the Universe there are several
grams of unseen mystery matter.
We know this from the way stars move. The Milky Way spins too fast
for the gravity of its visible material alone to hold it together.
The stars on the periphery would be flung off if there wasn't a
lot of extra material tugging at them. Other galaxies are the
same. There is also unseen stuff between galaxies binding them
into milling clusters. Taking the Universe as a whole, the way it
expands and the cosmic background heat radiation - the fading
afterglow of the big bang - all the evidence points to the
presence of a pervasive, hidden universe.
Theories of what this "dark matter" might be are legion, from
hordes of black holes to ghostly particles coughed out of the big
bang. Basically, though, there are three ideas. First there is
"dark energy", which behaves like invisible stuff smeared
uniformly across space. Observations suggest it could make up as
much as two-thirds of the mass of the Universe. Then there are
MACHOs, short for massive compact halo objects, such as brown
dwarfs. Astronomers have detected some, but far too few to make up
the remaining dark matter.
Finally there are subatomic particles like neutrinos. These
ghostly entities hardly interact at all with other matter, and are
so inconspicuous that most of them penetrate the Earth unnoticed.
There are also a lot of them, outnumbering the atoms in the
Universe by a billion to one. But neutrinos probably all have a
very low mass, and so make only a modest contribution to the total
inventory of dark matter. Theorists conjecture the existence of
other deeply penetrating particles that would have a substantial
mass, known collectively as Wimps, for Weakly Interacting Massive
Particles, and experiments are under way to try to snare one.
More exotic ideas, such as matter hidden in a fourth space
dimension, or inhabiting a shadow universe, have also been
proposed. Probably the cosmic dark matter is a cocktail of
many things, some of them as yet undreamed of. Whatever it
may be, it seems that ordinary atoms of the sort we and the Earth
are made from represent only a tiny impurity in a universe
dominated by Something Else.
1. Astronomers have caught a peek
at a rare moment in the final stages of a star's life: a
ballooning shroud of gas cast off by a dying star flicking on its
stellar light bulb. The Hubble telescope has captured the
unveiling of the Stingray nebula (Hen-1357), the youngest known
planetary nebula. Twenty years ago, the nebulous gas entombing the
dying star wasn't hot enough to glow. The Stingray nebula
(Hen-1357) is so named because its shape resembles a stingray
fish. Images of a planetary nebula in its formative years can
yield new insights into the last gasps of ordinary stars like our
Sun.
2. The Key Project team used this Hubble telescope view of the
magnificent spiral galaxy, NGC 4414, to help calculate the
expansion rate of the universe. Based on their discovery and
careful brightness measurements of variable stars in this galaxy,
the Key Project astronomers were able to make an accurate
determination of the distance to the galaxy. The resulting
distance to NGC 4414, about 60 million light-years, along with
similarly determined distances to other nearby galaxies,
contributes to astronomers' overall knowledge of the expansion
rate of the cosmos, and helps them determine the age of the
universe.
3. Located some 13 million light-years from Earth, NGC 4214 is
currently forming clusters of new stars from its interstellar gas
and dust. In the Hubble image, we can see a sequence of steps in
the formation and evolution of stars and star clusters. The
picture was created from exposures taken in several color filters
with Hubble's Wide Field Planetary Camera 2. NGC 4214 contains a
multitude of faint stars covering most of the frame, but the
picture is dominated by filigreed clouds of glowing gas
surrounding bright stellar clusters.
4. When 19th century astronomer Sir John Herschel spied a swirling
cloud of gas with a hole punched through it, he dubbed it the
Keyhole Nebula. Now the Hubble telescope has taken a peek at this
region, and the resulting image reveals previously unseen details
of the Keyhole's mysterious, complex structure. The Keyhole is
part of a larger region called the Carina Nebula (NGC 3372), about
8,000 light-years from Earth
3. Was Einstein's antigravity really a mistake?
Einstein called it his biggest blunder. But he may have been right
after all to include a type of antigravity called the cosmological
term to his general theory of relatively.
The extra term gives space a repulsive property: it pushes itself
apart, making it expand faster and faster. Einstein added this
fudge factor because the Universe was thought to be static, so
something was needed to balance the gravitational pull of matter
to prevent the Universe collapsing. But in the 1920s, Edwin Hubble
found that the Universe is actually expanding, so Einstein
abandoned the "cosmological constant" in dismay.
But the idea has refused to die. The quantum theory of fields
predicts that even empty space is seething with energy, the
gravitational effect of which precisely mimics Einstein's
antigravity force (this is the dark energy referred to in question
2). The theory is vague about the actual strength of the
repulsion, but puts a guesstimate value on it.
About five years ago, however, astronomers found that the
expansion rate of the Universe seems to be picking up and put
their own "experimental" value on the strength of the antigravity
force. To the theorists' bafflement, the astronomers made it about
120 powers of 10 smaller than the theoretical guess.
It's an exasperating result. If the constant were zero, a profound
law of nature might account for it, but a non-zero number that is
so small compared to theory is very hard to explain. To make
matters worse, cosmologists like the idea of a very strong cosmic
repulsion during the first split second after the big bang,
because this underpins the popular scenario of an inflationary
universe. According to this theory, the Universe abruptly jumped
in size by an enormous factor just after it was born, driven by a
pulse of intense antigravity.
So if we want to keep inflation and account for today's
accelerating expansion, we need a theory that explains why
antigravity was once intense, then drooped precipitously, and
after that hovered at just above zero. In other words, we want to
know why the antigravity force was almost but not quite totally
eliminated in the primeval phase of the Universe.
One possibility is that the force fades with time. Another is that
it varies in space, so that far beyond the limit of our telescopes
it may be much bigger. If it were, the matter in that region would
have flown apart too fast for galaxies and stars to form, so it's
unlikely there would be any observers around to measure the force.
This explanation assumes that the cosmological term in our part of
the Universe is small purely by accident.
What we need is a theory that derives the strength of the
antigravity force as part of a unified description of all the
forces of nature. Unfortunately existing candidate theories, such
as superstrings and M theory, do not seem to pin down this
particular number, and its tiny value remains mysterious. So we're
back to question 1.
1. A star 40 times more massive
than the Sun is blowing a giant bubble of material into space. In
this colorful picture, the Hubble telescope has captured a glimpse
of the expanding bubble, dubbed the Bubble Nebula (NGC 7635). The
beefy star [lower center] is embedded in the bright blue bubble.
The stellar powerhouse is so hot that it is quickly shedding
material into space. The dense gas surrounding the star is shaping
the castoff material into a bubble. The bubble's surface is not
smooth like a soap bubble's. Its rippled appearance is due to
encounters with gases of different thickness. The nebula is 6
light-years wide and is expanding at 4 million miles per hour (7
million kilometers per hour). The nebula is 7,100 light-years from
Earth in the constellation Cassiopeia
2. Just weeks after NASA astronauts repaired the Hubble Space
Telescope in December 1999, the Hubble Heritage Project snapped
this picture of NGC 1999, a nebula in the constellation Orion. The
Heritage astronomers, in collaboration with scientists in Texas
and Ireland, used Hubble's Wide Field Planetary Camera 2 (WFPC2)
to obtain the color image.
3. The Hubble telescope has spied a giant celestial "eye," known
as planetary nebula NGC 6751. The Hubble Heritage Project is
releasing this picture to commemorate the Hubble telescope's tenth
anniversary. Glowing in the constellation Aquila, the nebula is a
cloud of gas ejected several thousand years ago from the hot star
visible in its center. Planetary nebulae have nothing to do with
planets. They are shells of gas thrown off by Sun-like stars
nearing the ends of their lives. The star's loss of its outer,
gaseous layers exposes the hot stellar core, whose strong
ultraviolet radiation then causes the ejected gas to fluoresce as
the planetary nebula.
4. The Hubble telescope continues to capture stunning, colorful
snapshots of stellar burnout. These images reveal the beauty and
complexity of planetary nebulae, the glowing relics of Sun-like
stars. This image of NGC 7027, for example, is one of the first
infrared views of planetary nebulae taken with Hubble's infrared
camera. In this picture, Hubble peers through the dusty core of a
young planetary nebula to reveal the bright, central star. This
picture also captures a young planetary nebula in a state of rapid
transition
4. Why do we live in three dimensions?
"Maybe space is actually not
three-dimensional at all, but only appears that way to us. It
could have 9 or 10 dimensions, maybe more"
Is it just a fluke that space has three dimensions, or is there a
deeper explanation? Some theories speculate that space emerged
from the big bang with three dimensions just by chance, and that
there may be other regions of the Universe with a different
number.
Logically there is no reason why the Universe should not have,
say, only two dimensions. A hundred years ago, Edwin Abbott wrote
Flatland, an account of a two-dimensional world in which
beings lived their lives confined to a surface. But the physics of
a 2D world would probably be very different from ours. For
example, waves wouldn't propagate cleanly as they do in 3D,
raising all sorts of problems about signalling and information
transfer. And since conscious life depends on accurate information
processing, these differences might be enough to rule out our
observing such a region.
Going above three dimensions brings different problems. For
example, planetary systems would be impossible because the inverse
square law of gravity becomes an inverse law of higher powers. So
it seems that a three-dimensional world might be the only one in
which physicists could exist to write about the subject.
But there are hints that this question is based on a false
assumption. Maybe space is not three-dimensional at all, but only
appears that way to us. It could have 9 or 10 dimensions, maybe
more. Some theories aiming to unify the forces of nature, such as
superstring theory, invoke the existence of more dimensions than
those we see.
They do this because the equations describing what is going on
often work out better when they are given a higher number of
dimensions in which to operate. It is not exactly a fudge: extra
dimensions have a history of solving the most pressing problems in
physics. Einstein needed a fourth dimension, time, to correctly
describe gravity, for example. And Theodor Kaluza added another
space dimension in an attempt to unify gravity with Maxwell's
equations for electromagnetism.
Of course, we can't see the extra dimensions, but there may be a
reason for that. They could be rolled up extremely small. Imagine
viewing a hosepipe from afar: it looks like a wiggly line. On
closer inspection, the line is revealed as a tube, and what was
taken to be a point in three-dimensional space could be a tiny
circle going around a fourth space dimension that's too small to
detect.
It is possible to conceal any number of extra dimensions this way.
Unfortunately, however, superstring theory does not yet predict
three unrolled dimensions, so it cannot offer a convincing
explanation for our experience of the Universe.
But there is another way to conceal a higher dimension. Suppose
physical forces restrict light and matter to a three-dimensional
sheet or "membrane", while allowing some physical effects to
penetrate into the fourth dimension. The inhabitants of
Flatland perceived three-dimensional objects as
two-dimensional projections into their place: a sphere, for
example, looked like a circle. In the same way, although we see
only three dimensions, what we do see could be a mere slice or
section from higher dimensions.
Our "three-membrane" space need not be alone in four dimensions.
There could be other membranes out there similar to our
three-dimensional membrane, but sitting in a four-dimensional
space. It will take as yet untried experiments to confirm the
existence of a fourth spatial dimension, but it was recently
suggested that the collision of two such membranes might explain
the big bang. So the fact that we're here at all might eventually
be considered evidence that space isn't really three-dimensional.
1. A new golden era of space
exploration and discovery began April 24, 1990 with the launch and
deployment of the Hubble telescope. Over the past six years
Hubble's rapid-fire rate of unprecedented discoveries has
invigorated astronomy. Not since the invention of the telescope
nearly 400 years ago have astronomers' vision of the universe been
so revolutionized over such a short stretch of time. This picture,
released to commemorate Hubble's sixth anniversary, shows several
blue, loop-shaped objects that are actually multiple images of the
same galaxy. The duplicate images were produced by a cosmic lens
in space: the massive cluster of yellow elliptical and spiral
galaxies near the photograph's center. This cosmic lens, called a
gravitational lens, is created by the cluster's tremendous
gravitational field, which bends light from a distant object and
magnifies, brightens, and distorts it. How distorted the image
becomes and how many copies are made depends on the alignment
between the foreground cluster and the more distant galaxy
2. What appears as a bird's head, leaning over to snatch up a
tasty meal, is a striking example of a galaxy collision in NGC
6745. The "bird" is a large spiral galaxy, with its core still
intact. It is peering at its "prey," a smaller passing galaxy
(nearly out of the field of view at lower right). The bright blue
beak and bright, whitish-blue top feathers show the distinct path
taken during the smaller galaxy's journey. These galaxies did not
merely interact gravitationally as they passed one another; they
actually collided
3. This ghostly apparition is actually an interstellar cloud
caught in the process of destruction by strong radiation from a
nearby hot star. This haunting picture, snapped by the Hubble
telescope, shows a cloud illuminated by light from the bright star
Merope. Located in the Pleiades star cluster, the cloud is called
IC 349 or Barnard's Merope Nebula.
4. From ground-based telescopes, this cosmic object -- the glowing
remains of a dying, Sun-like star -- resembles the head and thorax
of a garden-variety ant. But this dramatic Hubble telescope image
of the so-called "ant nebula" (Menzel 3, or Mz 3) shows even more
detail, revealing the "ant's" body as a pair of fiery lobes
protruding from the dying star.
5. Is time travel possible?
Maybe this should be question 1. Forget dark matter and quantum
gravity, this is the question everyone would love to answer.
Time travel has been a favourite science fiction theme ever since
H.G. Wells's trailblazing novel The Time Machine. But not
everything it describes is science fiction: travelling forwards in
time, for example, is a proven fact. Einstein's theory of
relativity predicts that an observer moving relative to Earth can
leap into Earth's future, and the effect has been confirmed using
atomic clocks. Dramatic time warps require speeds close to that of
light, which is possible in principle but would take a major feat
of engineering, not to mention a lot of money.
Going back in time is far more problematic. Relativity does not
rule out an observer being able to make a journey through
space-time and return to their past. But all scenarios so far
discussed require exotic circumstances.
One way to go back in time is to use a wormhole in space.
Theorists speculate that such a tunnel - or star gate - linking
two points in space-time, really might exist. Find one and you
could jump through it, coming out moments later in another part of
the Universe. They also suggest that if wormholes do exist, then
one could be adapted to form a time machine. You could go through
it and exit not only somewhere else, but "somewhen" else too. And
that could be in the future or the past.
If it were possible to visit the past then all sorts of paradoxes
ensue, of course, such as the conundrum of the time traveller who
goes back and murders his mother when she was still a baby.
Paradoxes can be avoided by insisting that nothing can defy the
principle of cause and effect, but two-way time travel is still
very weird.
If certainly seems too anti-rational for some physicists. Stephen
Hawking suggested a "chronology protection conjecture", surmising
that something would intervene to prevent physical objects or
influences looping back in time. This may occur because of
fundamental physical obstacles to constructing a time machine; for
example, quantum vacuum energy might surge without limit near the
entrance to the wormhole, in effect blocking it.
The conjecture remains unsolved, but it's not a problem that many
people can devote time and effort to. As Hawking has noted, it's
hard to get funding for time travel research. So it is likely that
a proof or disproof will have to wait for solutions to more
general problems, such as producing a tractable theory of quantum
gravity.
1. A nearby black hole is hurtling
like a cannonball through the disk of our galaxy. The detection of
this speed demon is the best evidence yet, some astronomers say,
that stellar-mass black holes — those that are several times as
massive as the Earth's Sun — are created when a dying, massive
star explodes in a violent supernova. The stellar-mass black hole,
called GRO J1655-40, is streaking across space at a rate of
250,000 miles per hour, which is four times faster than the
average velocity of the stars in that galactic neighborhood. At
that speed, the black hole may have been hurled through space by a
supernova blast.
2. Rising from a sea of dust and gas like a giant seahorse, the
Horsehead nebula is one of the most photographed objects in the
sky. The Hubble telescope took a close-up look at this heavenly
icon, revealing the cloud's intricate structure. This detailed
view of the horse's head is being released to celebrate the
orbiting observatory's eleventh anniversary. Hubble was launched
by the Space Shuttle Discovery on April 24, 1990 and deployed into
a 360-mile-high Earth orbit on April 25. Produced by the Hubble
Heritage Project, this picture is a testament to the Horsehead's
popularity. Internet voters selected this object for the orbiting
telescope to view.
3. Planet formation is a hazardous process. New pictures from the
Hubble telescope are giving astronomers the first direct visual
evidence for the growth of planetary "building blocks" inside the
dusty disks of young stars in the Orion Nebula, a giant "star
factory" near Earth. But these snapshots also reveal that the
disks are being "blowtorched" by a blistering flood of ultraviolet
radiation from the region's brightest star, making planet
formation extremely difficult.
4. Eta Carinae may be about to explode. But no one knows when - it
may be next year, it may be one million years from now. Eta
Carinae's mass - about 100 times greater than our Sun - make it an
excellent candidate for a full blown supernova. Historical records
do show that about 150 years ago Eta Carinae underwent an unusual
outburst that made it one of the brightest stars in the southern
sky. Eta Carinae, in the Keyhole Nebula, is the only star
currently thought to emit natural LASER light. This just-released
image taken last September resulted from sophisticated
image-processing procedures designed to bring out new details in
the unusual nebula that surrounds this rogue star. Now clearly
visible are two distinct lobes, a hot central region, and strange
radial streaks. The lobes are filled with lanes of gas and dust
which absorb the blue and ultraviolet light emitted near the
center. The streaks remain unexplained. Will these clues tell us
how the nebula was formed? Will they better indicate when Eta
Carinae will explode?
6. Are we living in a cosmic colander?
"Relativity does not rule out making a
journey through space-time and returning to the distant past"
Familiar through black holes may now be, they could still spring a
few nasty surprises on theoretical physicists. A black hole may
form when a larger star burns out. The core collapses in a split
second, crushed by its own enormous gravity. If the material were
exactly spherical, by symmetry all the matter would fall radically
towards a point at the geometrical centre of the core, so the
density and gravitational field there would escalate to infinity.
Since gravity manifests itself as a warp in the geometry of
space-time, the curvature of space-time would also become
infinite, creating a sort of edge or boundary to space and/or
time. Mathematicians call this a singularity.
No one knows what to make of singularities. Does space-time really
end there, or do singularities merely signal a breakdown of our
theory? If space-time did have a boundary, then it would be
impossible to predict what might come out of it. Since prediction
and determinism form the basis for any rational scientific picture
of the world, singularities would mark a line beyond which science
can't set foot.
With a black hole enveloping it, though, at least the
singularities are veiled, and not quite such as threat. In 1967,
Roger Penrose proposed a "cosmic censorship hypothesis", saying
that all singularities formed by gravitational collapse should be
decently clothed by a black hole and thus rendered unobservable to
us. The alternative - the existence of a "naked" singularity that
could bring about events that have no rational cause - was
regarded as abhorrent.
Then, a few years later, Stephen Hawking provided a new twist on
the problem. He discovered that black holes would emit heat
radiation and slowly evaporate away. Theorists puzzled over what
becomes of them in the end: does this evaporation eventually
expose the singularity at the black hole's heart?
The issue has been rephrased in the language of information
theory. When a star collapses to form a black hole, the
information content of the star - how many particles it contains
of each type, say - becomes inaccessible to an external observer.
So when the black hold evaporates, is that information given back,
encoded somehow in the Hawking radiation? Or does it go down the
singularity plughole and disappear for good? Black holes appear to
be pretty much ubiquitous in our Universe. If a singularity marks
a hole in space-time, is the Universe leaking information like a
cosmic colander? And if so, where does it all go?
1. Glowing like a multi-faceted
jewel, the planetary nebula IC 418 lies about 2,000 light-years
from Earth in the constellation Lepus. In this picture, the Hubble
telescope reveals some remarkable textures weaving through the
nebula. Their origin, however, is still uncertain.
2. The Hubble telescope has captured an image of an unusual
edge-on galaxy, revealing remarkable details of its warped dusty
disk and showing how colliding galaxies spawn the formation of new
generations of stars. The dust and spiral arms of normal spiral
galaxies, like our own Milky Way, appear flat when viewed edge-on.
This Hubble Heritage image of ESO 510-G13 shows a galaxy that, by
contrast, has an unusual twisted disk structure, first seen in
ground-based photographs.
3. A nearly perfect ring of hot, blue stars pinwheels about the
yellow nucleus of an unusual galaxy known as Hoag's Object. This
image from NASA's Hubble Space Telescope captures a face-on view
of the galaxy's ring of stars, revealing more detail than any
existing photo of this object. The entire galaxy is about 120,000
light-years wide, which is slightly larger than our Milky Way
Galaxy. The blue ring, which is dominated by clusters of young,
massive stars, contrasts sharply with the yellow nucleus of mostly
older stars. What appears to be a "gap" separating the two stellar
populations may actually contain some star clusters that are
almost too faint to see. Curiously, an object that bears an
uncanny resemblance to Hoag's Object can be seen in the gap at the
one o'clock position. The object is probably a background ring
galaxy.
4. The Hubble telescope has snapped this remarkable view of a
perfectly "edge-on" galaxy, NGC 4013. This new Hubble picture
reveals with exquisite detail huge clouds of dust and gas
extending along, as well as far above, the galaxy's main disk. NGC
4013 is a spiral galaxy, similar to our Milky Way, lying some 55
million light-years from Earth in the direction of the
constellation Ursa Major. Viewed face-on, it would look like a
nearly circular pinwheel, but NGC 4013 happens to be seen edge-on
from our vantage point. Even at 55 million light-years, the galaxy
is larger than Hubble's field of view, and the image shows only a
little more than half of the object, albeit with unprecedented
detail.
7. How come I can ask these questions?
"It's sometimes said that life is written
into the laws of physics, but there's nothing in the know laws to
compel matter to organize itself into life"
Where does consciousness come from? Why do some swirling
electrical patterns, such as those in a brain, have thoughts and
sensations attached, whereas others, such as those in the national
grid, presumably do not? Conversely, how does something as
insubstantial as a thought or desire move electrons and ions
around in brains to trigger physical movement? Or are these
questions themselves a meaningless muddle of concepts? Are these
even questions for physicists to answer?
Some think they are for physicists to answer - myself among them.
Relating the mental and physical worlds is something most
physicists avoid, but if physics claims to be a universal
discipline then it must eventually incorporate a description of
consciousness.
Quantum mechanics has been cited as the key, largely because the
observer plays a central role in the description of quantum
systems. But it is far from clear whether quantum effects can ever
amount to much on the scale of neurons.
Perhaps the real key is to go back to descriptions of life. Nobody
knows how, or precisely when or where, life began. Somehow a
mixture of lifeless chemicals became a primitive living thing.
This is unlikely to have happened in a single dramatic leap;
doubtless there was a long and complicated sequence of physical
processes. But it is not even clear that this biogenesis is a
problem of physics per se.
It is sometimes claimed that life is written into the laws of
physics. Although it is true that life would probably be
impossible if the laws had been slightly different, there is
nothing in the known laws to compel matter to organize into life.
If a "life principle" exists in nature, it will be found not in
basic physical laws but in areas such as complexity and
information theory. After all, the living cell is not some sort of
magic matter, but a highly complex information processing and
replicating system.
The principles governing information and complexity are still
being worked out. At some level, quantum mechanics must play a
part in the story of life, as Erwin Schrodinger surmised in the
1940s. Since the rules for quantum information processing differ
dramatically from those for classical systems, perhaps that will
provide the key to solving this puzzle.
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Answering
Mysteries
Come