THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N, 70.2667° W
Founded January 1970
"Don't cry because it's over; smile because it happened."
THE DAILY ASTRONOMER
Tuesday. January 26, 2016
Tide of Questions II
We continue with part II of "Tide of Questions." Yesterday, we
posted answers to some of the many questions posed by students in
Portland's Breakwater School. (Hence the title "Tide of Questions."
ha ha*) Actually, the students submitted these questions to
Bernie Reim, author of the excellent "What's Up" column and co-host of
the weekly radio show "Radio Astronomy." Time did not allow Reim and
his blow hard cohort to address all the questions, so we thought we'd
answer them on the DA. We decided to devote two articles to the
effort, owing to the number of submitted questions.
Note that sometimes we will combine questions that are closely related.
We now cheerfully continue with our query cavalcade!
WHAT IS DARK MATTER ALL ABOUT?
Well, we still don't know. Astronomers are confident that dark
matter exists in great quantities. They've deduced its existence by
observing stellar motions in galaxies. Although dark matter doesn't
emit any detectable electromagnetic radiation (hence the term 'dark.')
it still exerts a gravitational influence on the visible matter around
it. Astronomers noticed that the stars in our galaxy are moving very
quickly. Such speeds are determined by the amount of matter within
the galaxy. The greater the amount of matter, the faster the
velocity.** Astronomer concluded that if the only matter in the
Milky Way were the visible matter, the stars would be moving much more
slowly. The physics of the issue is quire straightforward: there
has to be a lot more material within the Milky Way than we can see.
Some estimates suggest that 90% of the Milky Way consists of this
dark matter.
The problem is that we don't know its nature. Now, scientists have
only hypotheses about what it could be. One extraordinary
hypothesis suggests that gravity might be leaking into our Universe
from another one! We don't know what dark matter's nature, but
we do know of its existence.
WILL THERE BE ANOTHER BIG BANG?
There are a couple of ways to address this question. We'll begin
by quickly recalling that the Big Bang is the single event that most
cosmologists believe gave rise to the Universe out of the void.
It is believed to have occurred about 13.8 billion years ago. It
produced everything in the cosmos: space, matter, energy, and even
time. We cannot imagine that the Big Bang will happen again in
our Universe. However, remember that the Universe is expanding.
This expansion is accelerating with time, causing the Universe to grow
more rapidly. If some mechanism could possibly impede and
eventually reverse this expansion, the Universe could implode back in
on itself. Eventually, everything could be drawn back into a
singularity that would then explode as another Big Bang. This
reversal is known as "the Big Crunch." Based on what we know now,
it seems highly unlikely that such a 'crunch' will occur, as the
Universe is expanding faster now than it was in the past. Some
cosmologists wonder if eventually the Universe will literally rip
itself apart.
Also, it is possible that other 'Big Bangs' are occurring out in what
is called the "Multiverse." This multiverse is a hyperdimensional
region that spawns Universes almost like bubbles in water. On
this level, Big Bangs could be very common as one Universe after
another is brought into being.
NOTE: The sheer scale of the material Universe in both size and in
the variation of its component parts staggers the imagination.
WHEN WILL OUR GALAXY SUCK ITSELF UP INTO A BLACK HOLE? IS THERE
ANYTHING A BLACK HOLE CAN'T SUCK IN?
Black holes have bad reputations. They are, indeed, immensely
powerful entities, but they don't have the suction power that many
people believe. For instance, let's pretend the Sun turned into a
black hole. (It can't, of course, because it doesn't have enough
mass, but we're just pretending.) The Black Hole Sun, Mr. Cornell,
though very small, would still exert the same gravitational force on
the planets. Deprived of energy, the planets would be dormant, but
they wouldn't be sucked into the black hole like soap bubbles down a
drain. Only if an object approaches a black hole would it then
be trapped by its gravitational field and drawn into it.
Our galaxy contains a supermassive black hole in its center. The
stars orbit around it. (Next time your outside and looking at the
sky, realize that you are in a solar system that is moving at more
than 150 miles per second in a wide, 225 million year orbit around a
supermassive black hole.) Most galaxies likely contain these
supermassive black holes, but none of them will be consumed by them.
WILL GOING TO SPACE EVER BE "NORMAL" FOR A PERSON? WILL "REGULAR"
PEOPLE EVER GO?
One would think so. We recall (not directly, of course) that
Charles Lindbergh made history in 1927 by flying solo across the
Atlantic. Now, millions of people routinely fly across the Atlantic
every year. Flight is common place. Presumably, space flight might
eventually be common place, as well. Certainly, many science fiction
writers envisage a future world in which people zip back and forth
between planets as readily as they now hop from continent to
continent. The problem is logistics. As vast as Earth is, there
is oxygen everywhere. One can venture to the deepest jungle or
remotest desert and still have an abundance of air to breathe.
Ascending into outer space is far more problematic as travelers would
need to bring all their essentials with them, including water and
oxygen. Also, there is not as much of an impetus for people to go
into space...yet! Diplomats, business travelers, adventurers,
tourists travel all over the world to myriad destinations. Right
now, the only reason "regular" (i.e. non scientific) types of people
would want to go to space would be for the extraordinary experience of
being in space. Perhaps if some industries develop that require
space travel, more humans will lift off the surface and maybe space
travel will become commonplace, as well.
HOW DID THE BIG BANG HAPPEN?
We have no idea.
Cosmologists don't know how the Universe came to be. They believe
that it started with the Big Bang: an "explosive" event which created
space, time, matter and energy. What precipitated the Big Bang is a
mystery. The problem pertains to the phrasing. As time, itself,
started in the Big Bang, it is nonsensical to ask "what was before the
Big Bang?" because the word "before" is time relative. The M-Theory
posits that the collision of M-branes in a hyperdimensional
multi-verse might have spawned our Universe. From our limited
perspective, this collision appears as a birth from the void. Of
course, this is a theory. Nobody truly knows how the Big Bang
happened.
DO THEY STILL USE ROCKETS AT NASA?
Oh, yes, they do. While NASA is not currently capable of sending
humans into space (and the less said about that, the better), it is
still sending probes into space and satellites into orbit around
Earth. Deploying probes and satellites requires rockets that will
lift objects off the planet's surface. Firing material out of the
bottom of a rocket provides the "lift." Rockets are a particularly
powerful application of Isaac Newton's Third Law "Every action has an
equal and opposite reaction."
HOW ARE BLACK HOLES MADE AND COULD WE MAKE ONE?
Most black holes form when highly massive stars. Stellar
astronomers believe that a star has to be at least 20 times more
massive than the Sun to form a black hole. When such a star
exhausts its core fuel reserves, the outer layers collapse onto the
core, crushing it down into a very small volume. When the core is
still producing energy, the energy pressure pushes out, which prevents
the outer layers from falling in toward the core. When this energy
pressure abates, gravity pushes the outer material down. The
gravity then becomes immensely powerful because so much material is
compressed into a minuscule space.
We know of no mechanism by which we could compress matter down into
such a small space. To give you an idea, if you wanted to make
Earth into a black hole, you would have to crush the entire planet
down into the size of a marble. Good luck!
HOW DOES A BLACK HOLE HAVE SO MUCH GRAVITY?
What a black has is powerful surface gravity. Let's use Earth as
an example. Right now, every part of Earth is pulling on you
gravitationally. The parts closest to you, such as the material
right under your feet, is pulling on your harder than the parts
farther away, such as in Australia or Japan. Every particle pulls
on every other particle. The closer the particles are to each other,
the stronger the pull between them becomes. If, for instance, we
squeezed Earth so that it was smaller but still was just as massive,
then the distance between you and the parts of Earth farthest from you
would decrease and they would pull on you more strongly. The planet's
surface gravity would increase. Also, the escape velocity would
increase. "Escape velocity" is the velocity an object would need to
attain in order to escape from Earth. Right now, that velocity is
seven miles per second (25,200 miles per hour.) If Earth were
compressed into a smaller volume, its escape velocity would increase .
If we squeezed Earth down to the size of a marble (see the previous
question), Earth's escape velocity would equal the speed of light
(186,290 miles per second) and it would become a black hole.
WHY DO WE THINK THERE IS INTELLIGENT LIFE ON EARTH?
Yes, I stayed up late to watch the debates, too.
You're asking a very deep question, indeed. It involves the
definition of 'intelligence,' which is not straightforward. We
consider human intelligent because, at the base level, we are
'sentient,' or 'self aware.' Humans are parts of the Universe that
are aware of the Universe and ask questions about it. We also make
tools, communicate through intricate languages, and can perceive of
the remote future. We also ask questions about our origin and the
purpose of existence. Some would assert that merely asking the
question "Are we intelligent?" is, itself, evidence of intelligence
and therefore is self-referential, or is a question that answers
itself.
Intelligence, like everything else in the Universe, is a far more
complex matter than it might initially seem to be.
WHAT WILL NASA DO WITH THE 20 BILLION DOLLARS THAT THE GOVERNMENT JUST
GAVE THEM?
(Just for fun, go to a Libertarian web-site and post the same question.)
NASA is currently working on various projects. They are currently
constructing the James Webb Space Telescope, the next generation
orbiting telescope due to be launched in 2018. They are also
working on the Orion spacecraft: a vessel capable of transporting four
astronauts to the Moon and Mars. There is also the InSight Mars
Lander program. This lander is due to launch in about 2 - 3 years.
(It was originally slated to launch in March 2016.) Also, NASA is
working on Solar Probe Plus, the first mission to study the Sun's
corona. These are just a few of the current missions slated for
the near future.
WHAT IS THE FURTHEST THING FROM EARTH THAT HAS BEEN SEEN THROUGH A TELESCOPE?
As of now, the most distant object yet seen through a telescope is
EGSY8p7 (EGSY-2008532660), a galaxy 13.2 billion light years away. An
image of this object was captured by the Hubble Space Telescope and
in July 2015 was established as the most distant object yet observed.
This galaxy formed about 570 million years after the Big Bang. It is
an infant galaxy dating back to the early epochs of the Universe.
HOW DO WE EVER GET RID OF A BLACK HOLE?
Black holes stay around quite awhile, but they do eventually
"evaporate" through the emission of Hawking radiation. Hawking
radiation is a quantum physical effectt that permits particles close
to the event horizon escape. In so doing, this radiation wicks away
a small amount of the black hole's matter. At first, Hawking
radiation emission is slow. However, as a black hole loses matter
through this radiation and shrinks, the emission rate increases until
eventually the black hole evaporates altogether.
Of course -and this is an immensely important point- the evaporation
time for a stellar mass black hole is approximately
20,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
years!
For comparison, the current age of the Universe is 13,800,000,000 years!
Black holes vanish in very deep time.
IS A BLACK HOLE HOT OR COLD?
Generally quite cold. The internal temperature, according to
estimates, would be about a millionth of a degree above absolute zero.
(Absolute zero is minus 273.15 degrees Celsius.) Just outside of
the event horizon, the temperatures can be quite high if the black
hole is surrounded by an accretion disk: a disk of matter stripped
from a nearby stellar companion. The disc material rotates very
quickly close to the black hole, but more slowly farther away. This
differential rotation can generate temperatures in the hundreds of
million of degrees. For this reason, accretion disk tend to emit
copious amounts of X-rays.
CAN YOU GO SUPERSONIC TO ANOTHER GALAXY THROUGH BLACK HOLES?
Theoretically, black holes might be attached to wormholes, technically
called Einstein-Rosen bridges. These wormholes could provide conduits
to distant parts of the Universe or into another Universe, altogether.
These constructs are merely theoretical. Scientists don't know if
they actually exist.
Black holes might not be suitable for travel because of the powerful
tidal forces they exert. If you approached a black hole and came
within about 250 miles of one, the force exerted on your feet would be
millions of times more powerful than the force exerted on your head.
You would literally be ripped apart into your component subatomic
particles.
Supermassive black holes are much larger, so the force differential
would be less. One could, perhaps, use these black holes as
conduits, but, honestly, the risk is enormous. It is possible that
Einstein Rosen bridges, if they exist, collapse when material is
introduced into them. Not only dangerous, but unreliable.
DOES THE UNIVERSE END? HOW LONG DOES IT GO?
We don't know. We know that the observable universe is more than 13
billion light years in radius. Of course, we don't know how much of
the actual Universe consists of the observable one. It could be that
the Universe we see is a minute fraction of the entire system. So,
we know the observable Universe extends 13 billion light years in all
directions. We don't know if the Universe is boundless and far
larger than the one we can see.
HAD A DOG EVER BEEN IN SPACE?
Oh, yes. Many times. There have been 57 Soviet space missions in
which a dog was onboard. However, some dogs have been in space more
than once, so the number of dogs who've actually been in space is
about 37. The most famous of these is Laika, who, in 1957, was
the first animal to orbit the planet. Unfortunately, Laika died of
heat exposure during the descent. One should say Laika was the
first life form to orbit Earth, as Soviet cosmonaut Yuri Gagarin
became the first human to orbit the planet in 1961. It was a common
Soviet practice to place stray dogs in space, for mission scientists
were then unsure how space would affect living beings.
WHY IS THERE SPACE?
A beautiful metaphysical question. I wish I had a better answer, but
I don't. This question delves into the deepest realms of
philosophical speculation. Why does anything exist? What is the
fundamental nature of space and time? Why do we perceive them as we
do? As powerful as physics has proven to be, we cannot even begin
to address these questions with conventional scientific methods.
Physics enables scientists to describe how particles interact in space
and through time. The actual fabric of reality is, at least for
now, inexplicable.
ARE WE ALIENS?
Well, yes, actually, we are. If we eventually travel to other star
systems, we will be the aliens. We are not accustomed to thinking of
ourselves in this manner because we're all living on our home planet.
Of course, in every other part of the Universe, we would be the
aliens.
WHAT IS AN EVENT HORIZON?
An event horizon is the region around a black hole where light cannot
escape. What exists beyond an event horizon is largely
theoretical. Physicists know that a black hole should crush
itself down into a singularity: a mathematical point of no dimension.
We cannot directly observe this, of course, because such a
singularity would be enclosed in an event horizon.
WHY DON'T YOU AGE IF YOU ARE TRAVELING AT THE SPEED OF LIGHT?
Because time stops!
Time is velocity dependent. This means that when a vessel travels,
time dilates slightly. The faster the speed, the greater the time
dilation. Of course, at low speeds, such dilation effects are
negligible. Time dilation occurs because the speed of light is
constant in all inertial reference frames. For instance, let's say
that you are on a probe measuring the speed of a light beam. Somebody
at rest also measures the speed of the same light. You would both
arrive at the same value no matter how fast you're traveling. The
only way to explain this consistency in by the time frame. Your
time stream would be running slower than the time stream of the
stationary observer.
If your spacecraft could attain light speed, time would stop
altogether. Anybody on such a craft would not experience at time at
all, even if thousands of years elapsed in the Universe.
WILL THE UNIVERSE EXPLODE?
Probably not. However, the expansion of the universe is accelerating
and therefore it might rip itself apart eventually. Or, perhaps, the
Universal expansion might stop and it could then reverse back on
itself. This reversal could then implode the Universe, which might
then be reborn in another big bang.
*The joy of thinking I'm clever when I'm actually not is I get the
pleasure of feeling clever, anyway.
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