We're all living in a virtual world at present and will likely continue to reside within one for the foreseeable future. Consequently, our events are all on zoom, a sentence that would have baffled most people even a year ago. Today, we share many questions that students have asked us through the aether, or, at least on Zoom.
DO YOU THINK THERE WILL BE A SUPERMASSIVE BLACK HOLE? Oh, we KNOW there are supermassive black holes. Astronomers believe that supermassive black holes reside at the cores of most galaxies. Supermassive black holes can be millions of times more massive than the Sun and have event horizons that are as large as Mercury's orbit: an immense size for a black hole! CAN YOU HEAR IN SPACE? This answer will devastate "Star Wars" fans who love the roaring whoosh sound generated by spacecraft as they tear through the void. Unfortunately, no sound is possible in the outer space vacuum. Sound needs a medium. Were I suddenly to suck all of the air off Earth, I wouldn't be able to hear any sounds at all. On a side note, scientists once believed that a substance called"aether" pervaded outer space. They reasoned that such a medium was necessary so as to allow light, which travels as a wave, to propagate through space. Their attempts to detect the aether, most notably during the famous Michelson-Morley experiment (1887), were unsuccessful. Physicists now know that, unlike sound, light needs no medium through which to travel. WHY IS THE SUN YELLOW? Well, the Sun ISN'T yellow! When seen in outer space, the Sun appears white. Like all stars, the Sun generates light photons along all wavelengths. Each star has a "peak wavelength," defined as the wavelength at which a star generates its greatest amount of energy. The Sun's peak wavelength is about 500 nm (nm = one billionth of a meter), which is within the green part of the spectrum. The Sun appears yellow because of Earth's atmosphere, which scatters blue light around the sky. The yellow light isn't scattered and appears to define the Sun's color. Were we to remove the atmosphere, the Sun would appear intensely white. We'd have no sound, either. Of course, if the air were suddenly gone, that would be the least of our problems. WHERE DID THE BUBBLE COME FROM (THAT EXPLODED IN THE BIG BANG)? Here, we crash headlong into metaphysical speculation. Cosmologists, those scientists who study the history and structure of the Universe as a whole, cannot explain its ultimate origin. Physical laws break down within the very first fractions of a second after the Big Bang.. (0.00000000000000000000000000000000000000001 sec, to be specific.) This negligibly small time period following the Big Bang, defined as the "Planck Wall," is a profound mystery. We don't know how the Universe actually started. We also don't know what preceded the Universe's birth. There is even a problem with that question because that event created space, energy, matter and time. As time, itself, was created, the question "what was before the Big Bang?" is unaskable. WHAT COLORS ARE STARS? Stars can exhibit many colors. As mentioned previously in the segment pertaining to the Sun's color, a star produces light at various wavelengths. The star's temperature determines the peak wavelength. Cooler stars, such as Betelgeuse (in Orion) and Antares (in Scorpius), are cool and therefore appear reddish because they'll produce more red light than any other color in the visible spectrum. Hotter stars, such as Rigel (also in Orion), will appear blue-white, as they'll produce more higher energy blue photons than any other photons along the visible spectrum. Although we see the stars as non-descript white dots, the sky is actually brilliantly colorful. We can't perceive most of this color because our eyes cannot perceive color at low light levels. Stars can be blue-white, white, orange, or reddish. WHAT'S IN BETWEEN THE STARS AND PLANETS? Lots and lots of empty space! For instance, the nearest star to the Sun, Proxima Centauri, is 4.2 light years away. This distance is equal to about 25 trillion miles. If the Sun were a softball sized sphere in Portland, Maine, Proxima Centauri would be a small apple in Key West, Florida. Along with the empty space, of course, one can have vast swaths of dust. Denser regions of dust and gas collect in what we call "nebulae." Astronomers have to take this dust into account when observing stars, as the most distant stars will appear dimmer than they should be owing to the presence of obscuring dust. This obscuration is properly known as "interstellar extinction." ARE WE ALONE IN THE GALAXY? WHAT IS THE NEAREST PLANET THAT CAN SUSTAIN LIFE? WHEN WILL WE DISCOVER LIFE ON ANOTHER PLANET? We decided to combine these three questions as the phrase "We don't know" is an appropriate response for all of them. Presently, we only know of one life-harboring world in the Universe and we're living on it. However, it seems highly unlikely that Earth is the only such planet in the galaxy, let alone the cosmos. Astronomers have found more than 2000*** exo-planets (planets in orbit around other stars) and will most definitely discover tens of thousands more. From these discoveries, they estimate that the Milky Way Galaxy could contain hundreds of billions of planets. In fact, the planet population could surpass the star population. The greater the number of planets, the greater the likelihood that life exists elsewhere in the galaxy. Personally, it seems highly probable that the Galaxy teems with life forms, considering that our Universe is so prodigiously creative. We just don't yet know where the nearest hospitable planet is located or even if any exist. We also don't know when we will actually find any. HOW LONG DO PLANETS LAST? Well, that depends on the star around which the planets revolve. We know that the planets around the Sun will remain for billions of more years. Eventually, the Sun will expand into a red giant once it depletes its core hydrogen reserves. (The Sun fuses hydrogen into helium to generate energy.) The Sun will likely envelope and therefore incinerate Mercury, Venus and perhaps even Earth. However, it will never expand out to Mars. When the Sun eventually perishes and becomes a hot, planet-sized white dwarf, the other planets will remain in orbit around it. Now, more massive stars can explode as supernovae. Such an explosion is so powerful, it would obliterate the planets around it. Of course, the resultant debris could reconstitute itself to form a new planet. The short answer is that all the solar system's planets will persist for billions of years more.
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 happening out there 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 commonplace. Presumably, space flight might eventually be commonplace, 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 watch Presidential debates too. You're asking a very deep question, indeed. It involves the definition of 'intelligence,' which is not straightforward. We consider humans 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 conceive 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. HOW DO WE EVER GET RID OF A BLACK HOLE? Black holes stay around quite a while, 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 disks tend to emit copious amounts of X-rays. 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. HAS 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.
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