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Answering ALL Your Questions [Starts With A Bang]
“And in the end
The love you take
Is equal to the love you make.” -Paul McCartney
Every once in a while, I throw the chance out there (on facebook, twitter, or google+) to ask me whatever questions you want. Yesterday, for some insane reason, I invited people across all three platforms to ask me whatever they liked, with a dual promise that I’d not only answer them, but that the best ones would receive a free “The Year In Space” calendar for 2013, courtesy of the Planetary Society.
Image credit: The Planetary Society.
So I got a ton of questions, and now I’ll do my best to answer them as quickly but as comprehensively as possible. Let’s begin…
Image credit: Fayette County Public Schools, http://teach.fcps.net/immex/.
1.) Since you talked about Helium : What is the value of nitrogen in air for the body?
You might think “not much” at first; the nitrogen transferred into our blood through our lungs doesn’t play much of a biological role, whereas we need oxygen for some of our most vital biological functions. But that doesn’t mean we’d be happier if our atmosphere were 100% oxygen; quite to the contrary, we’d start suffering from some intense problems almost immediately. You’d accumulate fluid in your lungs, damage your pulmonary capillaries, experience chronic chest pains, reduce the amount of oxygen absorbed into the blood, and experience the collapse of many of your alveoli. Because your body doesn’t just need oxygen, it needs oxygen at a specific pressure, and if you breathed 100% oxygen at normal atmospheric pressure, these are the side effects. If you breathe oxygen at an enhanced pressure it gets even worse, and can result in nausea, dizziness, muscle spasms, and even seizures and convulsions. The way to fix this, if you want to breathe 100% oxygen, is to do so only at reduced pressure, which is what the Gemini and Apollo astronauts did. So the nitrogen in the air regulates the relative pressure of oxygen in your lungs; tinker with the balance at your own peril!
Image credit: Curt Renshaw.
2.) If faster-than-light communication worked, would there be a time-dilation in communication if one point were moving relativistically relative to the other?
So — first off — it doesn’t. There is, as far as we understand the laws of physics and the fundamental particles that exist, there is no faster-than-light communication. But this question represents a deep problem with why: if there were faster-than-light anything, then all of a sudden the notion of “events,” as in, what came first and what came second, is entirely dependent on how quickly and where you’re moving. If faster-than-light communication were possible, then it would also be possible to receive a message before it was sent. This is both impossible for obvious reasons, but also because special relativity forbids it. And happily so.
Image credit: Cosmic Inflation by Don Dixon.
3.) I’d love to know once and for all why Inflation precedes the Big Bang and not the other way around?
Briefly, the Big Bang is the idea that if you extrapolate further back into the past, the Universe was hotter, denser, smaller, and higher in energy. But you cannot go arbitrarily far back; there is an observed upper limit to what the energy density was in the past. You can also ask the question of whether anything could have happened to set up the Big Bang, and whether that thing would make any new predictions. That’s what inflation is: the thing that preceded and set up the conditions that were present at the earliest times where the Big Bang model matches up with our physical reality, and that’s why inflation precedes the Big Bang and not the other way around.
Image credit: DigitalGlobe.
4.) How hard is it to confirm or refute that North Korea sent up a satellite?
It’s very easy if you’re watching, and very hard if you’re not. A little more nuance: if you can’t catch them in the act, it becomes much easier to tell the sooner you find it, and becomes much more a game of detective-work the later you first find out about it. In this particular case, the evidence is pretty overwhelming that they did, but it would be much easier if we were continuously monitoring them from, say, geosynchronous orbit.
Image credit: Smoot Cosmology Group / Lawrence Berkeley Labs.
5.) How do we know there is more than the observable Universe, and do we know what’s beyond it?
By measuring the curvature of the Universe on the largest scales, we can determine whether it’s curved or not, and if it’s not, what the limits on curvature are. Through precision observations of the Cosmic Microwave Background, we’ve determined that if the Universe does close in on itself again, its physical size is at least about 150 times larger in radius than our observable Universe is. Based on the isotropy and homogeneity of what we see, it’s very reasonable to assume that beyond our observable Universe lies more Universe, indistinguishable from our own. More information here in this previous post.
Image credit: Decay (2012) – The LHC Zombie Movie.
6.) Have you seen the new CERN LHC Zombie movie, made by Ph.D. students?
No, I haven’t. But you can watch it here, if you’re interested. At some point years ago (maybe 2007 or 2008?), fellow cosmologist Robyn Levine made a zombie-attack video where a zombified version of myself attacked and ate a random stranger outside of the AAS meeting in Austin, Texas. But that’s as close as I’ve come.
Image credit: Olive Juice of http://greenlightcard.wordpress.com/.
7.) What is the source of Inertia?
Inertia, as we commonly use it, is a measure of how difficult it is to change an object’s momentum. If something is at rest, how difficult is it to accelerate it, and if something is in motion, how difficult is it to change that motion? For practically all terrestrial applications, this is the same as an object’s mass. So if you’re asking what the source of inertia is, it’s mass. If you’re asking “where does mass come from,” you can either blame the Higgs field and quantum chromodynamics, which is responsible for the mass of matter in our Universe, or baryogenesis, which is what created the matter that we’re made out of today.
Image credit: Quantum Optics Group at Ludwig-Maximilians-Universität München.
8.) Can quantum mechanics explain both the universe and the human brain/consciousness?
Quantum mechanics doesn’t explain the Universe so much as govern it. Some of the laws of physics are quantum mechanical in nature, and this applies to all particles and interactions in the Universe. It applies to the Universe and to the human brain equally. There are some phenomena in the Universe which require quantum mechanics to work (such as nuclear fusion in the Sun), and other phenomena for which quantum mechanics has no bearing (such as the orbit of the Sun around the galactic center). It is open to debate which category human consciousness falls into (i.e., we don’t know yet), but from my perspective, we would perceive ourselves to be conscious even in the absence of quantum mechanics.
Image credit: the Millenium Simulation at Max-Planck-Institute for Astrophysics.
9.) We refer to the universe as expanding or contracting as if it’s finite thing. If it’s doing either, what are the theories of what lies beyond our Universe?
It is expanding on large scales: groups and clusters of galaxies are expanding away from one another, moving farther and farther apart as time continues on. On small scales — within gravitationally bound groups and clusters — it is contracting in the sense that gravity will bring those objects together, resulting in mergers, in the future. On even larger scales than our observable Universe, there is simply more Universe, governed by the same laws as our own. People speculate about an even bigger scale, where there may be regions with different laws of physics, and where the Universe there is vastly different from our own. But these speculations are not based in our current understanding of physics, and have no evidence to support them. It doesn’t mean they’re wrong, but it means they’re beyond the scope of science right now. I’ll stick to my answer from question #5.
Image credit: NASA, ESA, and A. Feild (STScI).
10.) If we look in different directions, is the age [of the Universe] different? If not does this imply we are at the epicenter of the big bang?
The age of the Universe — and every measurable property of the Universe, in fact — appears to be the same in all directions. This is what we refer to as “isotropic,” and this observation tells us that the Universe has no preferred direction. When we combine it with the observation of “homogeneity,” or the fact that the Universe has the same apparent properties in all locations in space, it implies that all observers in our Universe would conclude that the age of the Universe is 13.7 billion years old, that it’s expanding with them (apparently) motionless at the center. But this is only an apparent illusion; isotropy and homogeneity in the context of general relativity ensures that there is no epicenter to the Big Bang, but rather that it occurred everywhere simultaneously 13.7 billion years ago.
Image credit: Wikipedia user Alethe.
11.) Who is John Galt?
The worst radio personality of all time, not in fact but in fiction. Those 100 pages at the end of Atlas Shrugged where he delivered his interminable soliloquy were some of the most painful I’ve ever read.
Image credit: 2012 Showtime Networks Inc. (of Tyson, anyway).
12.) In a one on one. Who would win? You or that Tyson guy?
I assume by “that Tyson guy” you mean this Tyson guy. I saw him in the Atlanta airport just last month and he was really nice, posing for photos with every passerby that wanted one. I’m younger, I’m in pretty good shape and I still have two ears, but I’d stand no chance against Iron Mike, and I know it.
Oh, that Tyson guy? He used to wrestle in college; that would actually be a potentially interesting bout. Put it together and we’ll donate all the proceeds to charity, and then we’ll find out!
Image credit: NASA, and I believe SDO.
13.) It’s my understanding that the Earth’s iron core helps to protect us from radiation from the Sun. If so, how?
It’s not so much that we have an iron core as much as we have an active core with a magnetic dynamo inside! This produces the large magnetic field at the surface of the Earth that’s sufficient to shield the Earth from high-energy charged particles emitted from the Sun. (Charged particles are bent by a magnetic field, and in the case of the Earth, our field bends particles that were headed straight towards us safely out of our way.) Without it, the Sun would eventually strip our atmosphere away, which is what we think happened to Mars, and why its atmospheric pressure is only 1/140th of what Earth’s is!
Image credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team; stitching of the HUDF and the XDF fields by me.
14.) When did you realize you wanted to study physics/astrophysics as a career? What would you be if you weren’t a physicist/professor/teacher?
When I was a senior in High School, I was in A.P. Physics, and hated it. Our teacher always showed up underprepared, and I felt like we weren’t learning any of the interesting things that the Universe had to offer, while my A.P. Chemistry classes had us studying electron structure of individual atoms and molecules. It was only in college that I realized that I did love physics, but I was fooled by a bad (for me) teacher. After I graduated, I taught High School, and it was while I was working in a job that I liked (but didn’t love) that I realized exactly what it was I’d rather be doing: learning in-depth about the physical Universe on the largest scales. I started graduate school in 2001 and I’ve never looked back. There are lots of other activities I enjoy and could have been happy doing, but I’m sure I’d choose astrophysics and cosmology all over again if I had to do it once more.
Image credit: A. Ahlbrecht, A. Alberti, D. Meschede, V. B. Scholz, A. H. Werner and R. F. Werner.
15.) How do John Stewart Bell’s “Six possible worlds of Quantum Mechanics” hold up today?
I have no idea. I have never encountered this essay, but I have tremendous respect for Bell’s work as far as the development of quantum mechanics goes. I’ve never found any appeal in alternative “interpretations” of quantum mechanics beyond Bohr’s original Copenhagen Interpretation; if they help you wrap your head around understanding what’s physically going on, by all means, investigate them. But no alternative offers any advantage as far as physical predictive power goes, and so I go with the easiest one to wrap my head around, which was the first one I learned.
Image credit: NASA / WMAP Science Team.
16.) How do physicists use the residual (CMB) radiation from the Big Bang to interpret the age of the Universe?
The beautiful thing about physical cosmology is that if you know what the Universe is made up of now, which is one of the things we learn from our great cosmic observations such as the CMB, large-scale structure, and distant supernovae data, and you also know how it’s expanding today, then you can figure out the entire expansion history of the Universe, including the amount of time that’s taken place since the Big Bang. Our “mix” today, of 4.5% normal matter, 22% dark matter, about 0.008% photons and the rest in the form of dark energy (adding up to 100%), combined with our measurements of the expansion rate of the Universe and the laws of General Relativity tightly constrain the age of the Universe to be about 13.73 billion years old. If the expansion rate is off by 2% then our age estimate is as well; if the CMB data indicated 5% more dark energy and 5% less dark matter the age would come out to just over 14 billion years, so it’s a very tight system.
Conceptually, we know what it’s doing now and what it’s made out of, and given that we understand how the Universe expands, there’s only one possible answer for the age of the Universe. Figuring it out from that is fairly straightforward; any properly educated physics or astronomy grad student could do this in their first year of studies.
Image credit: Unknown; assumed to be public domain.
17.) How does a black hole interact with the Higgs Field?
Come up with a working theory of Quantum Gravity and I’ll tell you. Seriously, physics breaks down before you get to the theoretical singularity of a black hole; at this point in time that’s not a question that physics has an answer to.
Image credit: Aaron Galloway of http://1023blakefm.com/.
18.) If I microwave a whole egg, it explodes. If I boil one, it doesn’t. Why?
This is a chemistry question, but one that I know the answer to. When you boil an egg, you cook it via heat transfer from the outside in. The chemical change that takes place in an egg that causes it to go from liquid to solid take place slowly in that environment, solidifying the egg inside without damaging the shell. (Conventionally, this is hard-boiling an egg.) However, the molecules inside the egg never exceed the temperature of the water they’re in, and thus the water molecules inside never boil. But when you microwave an egg, you increase the speed of the water molecules in the egg until they actually exceed water’s boiling point, and when you go from liquid-to-gas, the pressure inside the egg becomes too great for the shell to handle, and it explodes. You can test this by microwaving a hard-boiled egg; it still explodes. (I am not responsible for cleaning your damned microwave when you do this!)
Image credit: Adam Frank of the University of Rochester.
19.) Is our universe expanding out into an empty area?
A common misconception is that our expanding Universe is expanding “into” something; it is not. Imagine you have a rubber sheet, and you stretch it to be a 1′x1′ square, and you glue a few coins down onto it. Now you stretch it further, and it becomes a 2′x2′ square. Our galaxies are like the coins, and the rubber is like the space, but the coins aren’t expanding “into” anything; it’s space itself that’s expanding. Just as the rubber sheet exists in our higher-dimensional Universe, our 3-D space (+ 1-D time) could exist in a higher-dimensional spacetime (5D or higher), but that’s certainly not a necessity!
Image credit: Ray Kurzweil and Kurzweil Technologies, Inc.
20.) Do you think we will experience the singularity in our lifetime, and will it be positive or negative impact on science?
No; I do not think we will experience the singularity. Not during our lifetimes, and possibly not ever. The number of calculations-per-second will increase but not arbitrarily far into the future; physics has limits and so does information that can be calculated in a finite amount of time, even theoretically. Our feeble understanding of intelligence makes me very pessimistic about the technological singularity, both in our lifetimes and, conceivably, ever. If it does happen, sign me up at the end of my life to be downloaded into a computer, where I can enjoy a Moriarty-from-ST:TNG existence for all eternity.
Image credit: LSST / AURA.
21.) How is it possible for the energy density of empty space (e.g., Einstein’s cosmological constant) to do both, accelerate and make the universe stationary?
A cosmological constant is an energy inherent to empty space itself, a zero-point energy that is by definition non-zero. Unlike most forms of energy density, it has a negative pressure, which means that even though it has a positive energy, it causes spacetime to expand outwards. When Einstein first introduced it, his thought was that the Universe was static, but if it was filled with matter, it would collapse under the force of gravity. If the cosmological constant were tuned to just the right value, it would prevent the Universe from collapsing and keep it static. With the (modern) measured value of the cosmological constant (and the fact that the Universe is expanding, not static), we now known that it’s greater than that critical value, and thus it causes the Universe’s expansion to accelerate.
Image credit: NASA / STScI / Ann Feild.
22.) Will the Universe end in a Big Rip?
No. If dark energy is a cosmological constant — which it is, by all measurable indications — then no, there will be no Big Rip. There will be no turnaround, either, or a Big Crunch; there will be no cyclic behavior, or a Big Bounce. These all rely on a form of Dark Energy that changes over time, something that the suite of data we have about the Universe does not show. These are fun ideas to speculate about, and they come with interesting theoretical consequences, but let’s remember that the data is the ultimate arbiter of cosmology, and they best support a fate of indefinite expansion; no more, no less.
Image credit: me.
23.) Can you go over the multiverse theory a little more in depth?
This is as good as you’re going to get. There is too much background to summarize in just a paragraph, but let’s just say that in inflation, new regions of spacetime get created more quickly than inflation can end, and so even though our Universe may be infinite, there’s an even bigger infinity out there that’s still inflating.
Image credit: Lanru Jing, from http://www.sciencedirect.com/science/article/pii/S0165125007850061.
24.) What if Einstein was wrong and in fact we do live on an uber-large cylinder?
Our Universe is observed to be flat, topologically, and to have no repeating regions in it. If we do live on a very large cylinder, then the cylinder is sufficiently large that it is observationally indistinguishable from a Universe that is also spatially flat but not a cylinder.
Image credit: NASA, ESA and R. Massey.
25.) Does it not strike you as a bit odd Ethan that while Dark Matter is NOT evenly distributed in the Universe but Dark Energy IS, that professionals in your field think we’ll have the answer to the secret of Dark Matter first?
No. No it is not odd, and in fact it’s a very smart bet to make. Dark Matter has the potential to (although it doesn’t necessarily have to) interact in some non-trivial way with normal (baryonic) matter. If it does this, we will detect it directly, eventually. Dark matter does interesting things: it clumps, it was created at some point, and it may interact with itself or be able to be created in accelerators. With dark energy, there is no such possibility. Dark energy is (to be frank) a stupid name that we gave to an observed phenomena (the accelerated expansion of the Universe) that we have no idea how to detect directly. I am optimistic that we may find dark matter in my lifetime. I am pessimistic that we will understand dark energy any better than we do right now — maybe we’ll tack a few more significant figures on how indistinguishable it is from a cosmological constant — for generations to come.
Image credit: MPIfR Bonn; NASA, ESA and the Hubble Space Telescope.
26.) What do we see or currently predict in terms of large-scale electromagnetic effects on the cosmos?
They are negligible when compared to gravitational effects, but they are responsible for galactic-and-stellar-scale magnetic fields that are very interesting. Because the Universe is so electrically neutral (to at least one part in 10^43!) and charge separations are very difficult to maintain, gravitation is always the most dominant of the major forces on large scales, and the larger the scale you’re dealing with, the more important gravity is relative to the other forces. I should know, I wrote papers on it and it was an integral part of my Ph.D. Thesis!
Image Credit: NASA, ESA, R. Ellis (Caltech), and the HUDF 2012 Team.
27.) I want to know how far away the farthest galaxy is. And where it might actually be right now, given that we are looking billions of years into the past.
The farthest galaxy we’ve detected so far is at a redshift of 11.9, which means the Universe was only 380 million years old when the light we’re observing now from it was emitted. Right now, this galaxy is some 32.9 billion light years away, thanks to the expansion of the Universe, but there are going to be galaxies and proto-galaxies even farther away than that; the James Webb Space Telescope will undoubtedly find them! In theory, the farthest galaxy will be close to 46 billion light years away, which is the radius of the observable Universe.
Image credit: Eugenio Bianchi, Carlo Rovelli & Rocky Kolb.
28.) The universe has zero net energy, provided that the universe is completely flat. What does a flat universe mean?
“They say ‘A flat ocean is an ocean of trouble. And an ocean of waves… can also be trouble.’ So, it’s like, that balance. You know, it’s that great Oriental way of thinking, you know, they think they’ve tricked you, and then, they have.” -Nigel Tufnel
Let’s ignore the “zero net energy” part, since energy is not even defined in General Relativity. To be flat, that just means that spatial curvature — whether the spacetime Universe is positively or negatively curved — is indistinguishable from zero. Which is what we observe. Hence, the Universe is flat.
Image credit: NASA and ESA.
29.) Could you give us a view on the way we are able to look back billions of years in time when looking at distant stars?
The Universe is a finite age, and light takes a finite time to travel. Anything we look at is only as old as we are, minus the amount of time it took light to travel. So if we’re 13.73 billion years old and we’re looking at the Moon, the Moon is the same age as we are, minus about 1.3 seconds. If we’re looking at a star 800 light years away, that star is the same age as us, minus 800 years. And if we’re looking at a galaxy who’s light has been traveling towards us for 12 billion years, then we’re seeing that galaxy when it’s the same age as we are, minus 12 billion years. Eventually, this gets to be significant!
Image credit: http://undsci.berkeley.edu/article/howscienceworks_01.
30.) If math is an abstract system that exists in our minds, why do the predictions of those rules agree so amazingly well with the physical world?
Because science works! It’s actually the other way around, to be honest. You can imagine a Universe that didn’t obey scientific rules: where gravity accelerated objects downwards at 9.8 m/s^2 one moment and didn’t work at all the next. Where your atoms held together in the form of a human being one day and simply ceased to do so another. We’re not at the point where we can derive the laws of physics purely from mathematical principles; that isn’t how physics works. The math is a guide that provides self-consistent possibilities for what could happen, and the physics — the physical world — is the ultimate arbiter. If the predictions of those rules didn’t agree with the physical world we’d live in a Universe of total chaos, where unpredictability was the rule and there were no exceptions. But, for whatever reason, we’re lucky, and the Universe appears to obey the same rules everywhere we look, and at all times.
Image credit: Alien, Resurrection (1997), via http://www.filmedge.net/alien/photos.htm.
31.) If we ever make contact with sapient alien life, who do you think will be better looking, us or the aliens?
To us? We will. To them? They will. Hopefully they’ve evolved to be attracted to their own species, just as we’ve evolved to be (mostly) attracted to our own. I hope.
Image credit: Alan Friedman.
32.) Is the Moon visible in the sky during more daylight hours or during more nighttime hours, and why?
On average, the Moon is visible during 12 hours out of every day. During months where days are longer, it’s preferentially visible more during the day, and during the months where nights are longer, it’s preferentially visible more during the night. Over the course of a year, it’s visible for six months, where 3 of those occur during daylight hours and 3 occur during night hours. However, the Moon is much more easy to see at night when the Sun isn’t illuminating the sky, and so we associate the Moon with night much more freely than we associate it with day, even though it spends just as much time in the daytime sky over the course of the year.
Image credit: Voyager spacecraft; timelapse.
33.) Is it really possible for ‘technologically superior’ alien overlords to convert the planet Jupiter into a star?
Sure. Just introduce it to about 40-to-80 more Jupiters (depending on whether you’ll settle for a brown dwarf or want a full-blown M-star) and let gravity do its thing. You’ll get a star as a result, but that’s really a lot of effort for such a paltry result.
34.) How old were you when you wrestled your first bear?
Uhh… well, someone did make this picture of me a little over a year ago…
Image credit: No idea.
…does that count?
Image credit: wikipedia user Danial79.
35.) What planet has the lowest average distance from the Earth?
This is actually a fun one! Venus gets closest to the Earth when we swing by it, but Venus also gets farther away from us than Mercury does during half of the year (on average). It turns out that — if we’re willing to take an average over long (greater than 1 year) times — Mercury and Venus are practically tied for the average distance from Earth, and although the Sun isn’t a planet, it’s tied with them, too. (The outer planets then go in order: Mars, Jupiter, Saturn, etc.)
If you want to get slightly more technical, because of the mathematical geometry of circles, the Sun has a slightly lower average distance to Earth than the planet Mercury does, and Mercury has a slightly lower average distance than Venus; this is completely due to the fact that circular (or elliptical) orbits have greater distances from us than the Sun does when they make a right angle with respect to the Earth/Sun system. But this answer is only correct averaged over long periods of time; over (somewhat) short timescales, sometimes Mercury’s the closest, sometimes Venus is, and sometimes the Sun is.
Image credit: NASA's “SciJinks”, http://scijinks.nasa.gov/tidal-curiosities.
36.) What would be the effect of solar tides to the Earth-Moon system if Earth got tidally locked against the Moon?
This is a false question, and very dangerous! The Moon is an insufficient mass to tidally lock the Earth to it; if the Earth appeared to be tidally locked to the Moon it would be a temporary, transient condition, and tidal friction would continue to decelerate the spin of the Earth and lengthen the day. Sorry, Luna, you’re out of your league here.
Image credit: from http://www.mondolithic.com/.
37.) Is it possible for a black hole’s singularity to undergo inflation and form another Universe?
I don’t have enough evidence to say no, but I’m not going to be the one to venture inside to find out!
Image credit: Roth Ritter (Dark Atmospheres).
38.) If the Universe is so old why are there so many blue stars?
Because there’s still plenty of Hydrogen, and as long as there’s enough hydrogen to form new stars, any star more than about twice as massive as our Sun will be blue for the main stage of its life. The double cluster in Perseus, above, is estimated to be less than 6 million years old, which is a blink-of-an-eye for a 13.7 billion year old Universe.
Image credit: Aldo Spadoni.
39.) Let’s build a rocket. Stock it with everything a man may need in their life, man it with newborn child, and launch it with acceleration of 1g. Let’s assume we have a power source, technology, and CMB shield, which allows to maintain that acceleration for a lifetime. How far will the rocket get until the man dies in the age of 70?
If you did this for about 30 years, you could reach any galaxy in the Universe out to a redshift of about 4 or 5, which is where galaxies “red out,” or are already receding away from us faster than the speed of light. Time will pass normally for you in the ship, but by that point, billions of years will tick by with each day for you, and you’ll observe the Universe disappear around you even as you whiz through it. It’s a simultaneously glorious and horrifying way to spend your days!
Image credit: HETDEX (Hobby-Eberly Telescope Dark Energy eXperiment).
40.) We seem to need dark matter and dark energy to make our current equations match what we see for now. Is it possible to associate both ‘dark’s with one common field, e.g. where positive fluctuations would be dark matter and negative fluctuations would be dark energy (or vice versa)?
No; they are too different from one another. Dark energy appears to be a constant throughout the Universe, and it exists where there is lots of dark matter, small amounts of dark matter, and no dark matter at all; the dark energy density appears to be unaffected by anything else in the Universe! Dark matter, on the other hand, clumps gravitationally, and so it is interesting to think of it as a field or a collection of particles. But the two do not appear to be connected, other than they both have “dark” in their names.
Image credit: NASA / STS-125.
41.) If you aimed the Hubble Telescope, or a telescope of similar power at Earth, what would you see?
Hubble has a 2.4 meter primary mirror, which means that it has a diffraction-limited resolution of 0.05 arcsec, or 0.000014 degrees! Ignoring atmospheric distortion and overexposure from light, we can figure out the resolution of such a telescope. From low-Earth orbit, about 560 kilometers up, that means it could resolve objects down to a size of about 14 centimeters, or just under 6 inches. Of course, it’s field of view is so terribly narrow, and it flies over the Earth so quickly (it makes a complete orbit in less than 90 minutes) that it’s impractical for looking at Earth. But if we wanted to design an instrument to do so… we could spy on people with incredible resolution. (And we’re likely doing so; remember those two free Hubbles that were just gifted to NASA? Where do you think they came from?)
Thanks to everyone who asked such great questions; it never hurts to be curious! If you’ve made it this far, please comment and tell me which question, in your estimation, should win, and I’ll pick the winners based on your recommendations at the end of the weekend. (One vote per commenter, please.) Thanks as always for your interest in learning about the Universe; I’ll keep doing my best to share all I know and all I love about it with you!
2012-12-14 23:01:27
Source: http://scienceblogs.com/startswithabang/2012/12/14/answering-all-your-questions/
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