“There is a fine line between censorship and good taste and moral responsibility.” -Stephen Spielberg
Another week full of amazing science stories has gone by here at Starts With A Bang, and there are some fun and fantastic announcements! We welcomed a new contributor, Jess Shanahan, to our ranks; I found out that Forbes has made me their official Star Trek: Discovery reviewer when that new series premieres; I’m in the process of selecting the final, officially licensed images for my new book, Treknology (and pre-order today!); and from this coming Thursday through Sunday, I’ll be the Science Guest of Honor at NorWesCon in Seattle! Come if you can! Now, let’s take a look back at the past week of articles:
- What’s the difference between a fermion and a boson? (for Ask Ethan),
- Earth prepares to snap first-ever image of a black hole’s event horizon (for Mostly Mute Monday),
- Saturn’s moon Enceladus is our closest great hope for life beyond Earth (by Jess Shanahan),
- How much gold is in the James Webb Space Telescope?,
- ‘Project Blue’ aims to find planets around the nearest sun-like stars, and
- Can muons — which live for just microseconds — save experimental particle physics?
Thanks to our generous Patreon supporters, these articles appear ad-free on Medium one week from their original publication date. And now that it’s time to jump into this edition of our comments of the week, it’s also time to announce that any one-week bans we doled out have now expired. Welcome back to the fold, everyone, and remember to treat each other well!
Perceived knowledge vs. actual knowledge. Image credit: Justin Kruger and David Dunning, 1999.
From Denier on myside bias: “I’m not saying Scientists are bad for being wishy-washy intellectually as new information comes in. I myself am that way. I’m also not saying society is bad for being so tribal as it evolved for a reason. I just find it amusing when academics don’t realize they’ve incorrectly projected a trait where it doesn’t belong.”
I didn’t realize this was what your statement was attempting to convey. Yes, scientists are particularly good — they need to be or they won’t make it — at changing their mind in the face of compelling, overwhelming evidence. The general public is particularly bad at that, and particularly good at choosing sides and defending their side while attacking the opposite side regardless of the quality of the evidence. The further polarization of our society over the past 30 years thanks to the culture wars has arguably made this worse.
I like to think the way out will be evidence-based reasoning. That has proven to be naive so far.
Image credit: Universe Review.
From Michael Mooney on relativity and apparent versus real shapes: “You forget again that a contracted Earth is only “apparent,” i,e., that fast moving frames of reference do not change the physical shape of planets and stars. There is no physics to support shrinking planets and stars.”
On the contrary, Michael, it is only physics that supports a real length contraction. You see, the principle of relativity (and I’m oversimplifying by leaving out caveats here) is that the laws of physics are the same for all observers. If you move fast relative to anything else in the Universe, the laws of physics are the same for you as they are for anyone else. If you see an electron, it has an electric field with a total amount of field energy that’s identical to any other observer.
What happens if you’re at rest vs. in motion with respect to that electron? In order to keep the laws of physics the same, everything about that electron must change in a very particular fashion: its field lines must change, its spatial field density must change, the way a clock runs or distances behave must change, etc. Your measurements, from your perspective, show a real, physical departure from the measurements made aboard the electron, or in the electron’s frame, if you prefer.
The strength of the electric field lines will change in the direction of motion, if the charge is moving relative to you. Image credit: Carel Vandertogt.
That is physics. That is real. That you don’t like it (and/or don’t get it) doesn’t make it untrue.
When you say this: “I have never challenged the “big difference between what people see” in SR. I (and many other SR critics) only challenge the claim that those differences reflect actual physical variations in objects and distances. Yet no SR theorist will admit, “Yes, the differences are only apparent.””
I am puzzled as to what you’re contending. Are you saying that if you switch reference frames, or if you go to the rest frame of the object, then that’s the “true” physical size? That’s nonsense; all reference frames are equally valid. Are you claiming that physical objects aren’t really contracted in their direction of motion? They absolutely are, just like you and I are with respect to an incoming comet. It doesn’t change how we perceive ourselves or the measurements we make, but it’s a real, physical effect that occurs uniquely for every unique observer in the Universe.
Image credit: Fyodor Yurchikhin, of Greenland from the ISS.
From Lee Witt on contesting Denier’s claim that he reasons like a scientist: “Thank you for explaining your repeated refusal to understand the science of climate change – you prefer to believe the fake stories about the gloom and doom that you believe would result from addressing it rather than the mountains of evidence that support the scientists.”
Atmospheric carbon dioxide concentration is presently at a little over 400 parts per million. If fossil fuel emission rates continue at their current values, we will hit 900 parts per million around the year 2300, give or take about 50 years. The increasing CO2 is the primary driver behind the temperature increases on Earth, although the feedback effects are what make it so dire, devastating and inevitable. Cities on Earth are predominantly located in coastal regions or otherwise on the water. A 3 meter sea level rise will submerge about 1.5% of Earth’s current land mass. Melting the Greenland ice sheet will raise sea levels by 8 meters. Melting all the permanent ice on Earth will raise sea levels by more than 30 meters.
You can view this map for yourself and see what sea level rise does to the parts of the Earth you care about. If you truly contend to care about your kids and grandkids, and I believe you, why should I not hold you responsible for your actions and advocacies that damage the lives and livelihoods and destroy the homes and cities of the adults, children and grandchildren of others?
Heat-trapping emissions (greenhouse gases) far outweigh the effects of other drivers acting on Earth’s climate. Source: Hansen et al. 2005, Figure adapted by Union of Concerned Scientists.
From CFT on inexcusable reasoning: “…WHY many scientists don’t agree with the idea of carbon dioxide as being the climatic bogey man…”
Because they selectively ignore evidence. That’s it. There is no good reason for disagreeing with the idea. They ignore large portions of the full suite of evidence. That’s the reason. That might not be your reason or what you hear, but that’s the reason. It is motivated reasoning, plain and simple.
And when someone like Denier says: “No one has a model that perfectly predicts Earth’s atmosphere.”
That is true, but it’s also irrelevant. Yes, climate scientists are wrong in the sense that any science is wrong: there are some predictions that the theory cannot get right, and there are limits to the range of validity of what can be accurately predicted. But if you think that means that all climate science is garbage — or that a denialist model like Curry’s, Lindzen’s, or Easterbrook’s is just as good as the consensus model — then you have failed to understand some very basic principles of science. And remember, the quantitative estimates aren’t estimates that I made up; they are the best estimates I can find by the best scientists working on the problem. If you don’t like them, you are free to “believe” other estimates or come up with your own, but don’t expect anyone else to join you in your belief unless you expect them to abandon expertise (in this case) as you so willingly do.
But if you’re so convinced you’re right, why not go argue with the primary source? Why not become a climate scientist yourself and make sure the field gets it right? Why sit here and argue with an astrophysicist who sees extraordinary competence, scientific integrity and all the hallmarks of it being done right, about the finer points of something when you don’t even accept the coarsest points and the most robust conclusions of all?
The way that atoms link up to form molecules, including organic molecules and biological processes, is only possible because of the Pauli exclusion rule that governs electrons. Image credit: Jenny Mottar.
From John on the difference between fermions and bosons: “What a huge difference a half-integer spin makes!”
Yes! And in particular, what a huge difference obeying or not obeying the Pauli exclusion principle makes. It’s easy to sort of say, “big deal, so I need to put my second fermion somewhere else,” but when you have large numbers of fermions, this gets very impressive (and very important) very quickly.
Pair production and matter-antimatter annihilation. Image credit: Addison-Wesley, retrieved from J. Imamura / U. of Oregon.
From Anonymous Coward on particle/antiparticle collisions: “Colliding a photon with another photon though, under the right conditions, will cause a form of pair production, and it will become an electron-positron pair. What happens when two Z bosons of the weak interaction come together like that?”
Forwards/backwards reactions — or time-symmetric reactions — are the norm in physics. When it comes to the particles in the Universe, if you collide (in general) a particle with its antiparticle counterpart, you can pair-produce any particle/antiparticle pairs for which you have enough energy available, so long as you conserve energy and momentum. There are not major differences in that regard from colliding an electron/positron, quark/antiquark, neutrino/antineutrino, photon/photon, Z-boson/Z-boson, W+ with W-, gluon with its proper gluon counterpart, etc. Cross-sectional differences and the subtle CP-violation of the weak interactions aside, it’s all practically the same.
Michael Kelsey gave even more detail: “Z0 annihilation has not been directly observed (because we can’t make Z0 beams, of course), but the production of Z0 pairs in high energy collisions (at LEP2 and the Tevatron) has been observed. The principle of “detailed balance” means that you can invert that interaction to recognize that a Z-Z collision can produce the accelerator original state. The result should be equivalent to gamma-gamma (or more precisely gamma*-gamma*) interactions, with some pair of particles produced.”
Simulations of how the black hole at the center of the Milky Way may appear to the Event Horizon Telescope, depending on its orientation relative to us. These simulations assume the event horizon exists. Image credit: Imaging an Event Horizon: submm-VLBI of a Super Massive Black Hole, S. Doeleman et al.
From John on testing Einstein’s general relativity: “Directly imaging the event horizon of Sagittarius A* ! How cool is that?!?!?
Even better is the potential to use the Event Horizon Telescope to test EGR”
If General Relativity breaks down anywhere, the physics of black holes is likely the “where” of that. While the physical size of the event horizon (keep reading, Michael Mooney) has some very explicit predictions for it, what we expect to see as the size of the event horizon is quite a bit larger, thanks to the deformation of space in Einstein’s General Relativity. (Which I know is what you meant by EGR, even though everyone else calls it GR.) That 37 microarcseconds is a precise prediction, and if it doesn’t match up by any amount larger than our uncertainty in the black hole’s mass, that could be a very interesting measurement indeed!
Saturn’s E-Ring, as imaged here by Cassini, is created by it’s frozen Moon, Enceladus, ejecting icy material over time. Enceladus is the bright spot at the image’s center. Image credit: NASA/JPL/Space Science Institute.
From Jonathan on Saturn’s E-ring and Enceladus: “so on astronomical time scales, does the loss of matter to Saturn’s E-ring have a noticeable effect on the moon?”
One of the truly fantastic things about Cassini that most people don’t realize is how quantitative it is. Here’s a fun and relevant paper you may enjoy. During an eruption of Enceladus, particles leave the surface vents at a mean rate of about 51 kilograms/second, where 91% eventually fall back to Enceladus and the other 9% go into the ring. The total mass of the E-ring is approximately 1.2 billion kilograms, meaning that the particles live, on average, in the E-ring for only about 8 years. Do they get transferred to other moons or rings? Do they fall back to Enceladus? That Cassini hasn’t measured, but given that Enceladus has a mass of just over 10^20 kg, and that the Solar System is only ~10^17 seconds old, Enceladus still has most of its mass for certain as it did when the Solar System first formed.
Ice fishing here on Earth. Something tells me it would be slightly different on Enceladus. Image credit: Brücke-Osteuropa.
From Sinisa Lazarek on the future news headlines of Enceladus: “Daily News for October 19th 2098
*Breaking News*
– Japenese Orbital Fishing Fleet (JOFF), which recently arrived at Enceladus to begin harvesting native prawns (Penaeus Enceladus) discovers two structures beneath moons thick icy crust. JOFF’s prawn-sonars specially designed to cope with enceladus ice detected what seems to be a US secret military base, some 2 kilometers under the ice. The base seems to be located just below the north polar belt of enceladus. To further their amazement, they also discovered an old USSR submarine under the south polar cap of enceladus. Both locations seem to be long abandoned….”
This is some pretty good science fiction writing here.
A false-color image highlighting Saturn’s hurricane over its north pole, inside the much larger hexagon-shaped feature. Image credit: NASA/JPL-Caltech/SSI.
From Anonymous Coward on the physics of color: “We tend to think of certain wavelengths of light producing certain colours, but if you mix green (495-570 nm) and red (620-740 nm) light we see yellow. Did the mixing of colours cause the light we see to change wavelengths? No. The mixed light excites the M and L cones in our retinas equally, which the brain then interprets as yellow, the same as light in the 570-585 nm wavelength range would. There are even “imaginary colours” that cannot possibly be produced by any physical source of light. The eye has three different types of cones, the S, M, and L cones, and their sensitivities to the various wavelengths of light overlap.”
That’s the whole thing… when we talk about false color vs. true color, we talk about what your eyes can see. And while there’s a lot of physics behind color, there’s also a lot of biology behind color, too! The physics of color is about the wavelength of monochromatic light, or light of a particular wavelength, and that’s it. How our brains interpret it is far more interesting from a “what we see” point of view.
I did write a piece, years ago, answering the question of What Is Color?, if you’re interested, but I caution you that it goes right for the biology in short order, because “color” is inherently a human concept, too.
The 18 segments of James Webb in the laboratory, after completed assembly and all coatings have been applied. The gold is visually striking, but there’s very little of it. Image credit: NASA / Chris Gunn.
From Tomas Ahl on mirrors versus other electronics for James Webb: “To really answer the title question I assume there is more gold than that to make the whole thing? In electronic components, cable connectors etc. Would that accumulate to an equal amount to what is on the mirrors?”
I would also assume that there is lots of gold plating on the various electronic components, to eliminate oxidation yet maintain excellent conductivity while the telescope and instruments are still here on Earth. I sent this question off to a project scientist I know who works for Northrup Grumman, and they didn’t know they answer either. So my guess would be no, because I can’t imagine that the surface area of all the exposed internal wiring is anywhere near what the surface area is for the mirrors themselves, but that’s a guess, not a calculation.
A simulation of what the next Pale Blue Dot would look like through this newly proposed telescope around Alpha Centauri A or B. Image credit: Project Blue Mission Team.
From MobiusKlein on Project Blue for more stars: “For the notion of ‘one shot’, as in there is only one reasonable target to observe given the size of the scope, how much bigger and expensive would it have to be to get useful results from 100 stars?”
This is a good question! If you want to make the measurements Project Blue does for even a third Sun-like star, you need to go up by a factor of 2.5 in diameter: from 45 cm to about 1.3 meters. If you want to get 100 Sun-like stars, you’re talking about going out to about 10 parsecs, which is about 8 times as far as Alpha Centauri A and B. So 8 times a 0.45 meter mirror is about a 4-meter mirror. At present, that would be the largest space telescope ever launched. I would imagine we would be talking in the multi-billion dollar range for a mission like that. Sadly, to get 50 times as many stars would, indeed, be about 50 times as expensive.
Gravitational radiation, illustrated here, clearly occurs along more than one axis. Image credit: ESO / L.Calçada.
From Denier on the number of axes in forces: “We have a 1 axis force that is super long range but wimpy in gravity. Then we have a more powerful but shorter range 2 axis force in electromagnetism. Lastly we have a 3 axis color force that is so powerful it can literally pull matter into existence from nothing but is super short range. There is a weak force but it is really just an offshoot of the 3 axis color force. There is no 4 axis force.”
I’m sorry, but this is not how the fundamental forces work. Gravity is not a one-axis force at all, since it exerts tidal forces, shear forces, and gravitational radiation is a quadrupolar effect. If you want to learn about how the weak, electromagnetic and strong forces work as far as degrees of freedom go, the route you need to go down is group theory. The strong force obeys the rules of the SU(3) group; the electromagnetic obeys the rules of the U(1) group and the weak force obeys the rules of a chiral SU(2) group. Gravitation? Good luck there… whatever group you’re interested in is going to get way bigger than anything with the number “3” in it.
The production of a cosmic ray shower, produced by an incredibly energetic particle from far outside our Solar System. Image credit: Pierre Auger Observatory, via http://ift.tt/11Wasx4.
And finally, from Frank on cosmic ray muons: “How about using natural muons coming from sky?”
The hard problem with muons is collimation, which is why the MICE collaboration’s advances are so important. Cosmic ray muons occur at an approximate rate of one muon per human-hand (about 0.01 square meters) per second. We are looking for bunches of muons at the same energy, the same speed and the same trajectory that are produced in a consistent, controllable fashion. We will someday — for high enough energies — be forced to go back to cosmic rays. But for muons, that day has not arrived just yet!
Thanks for a great week, everyone; welcome back to the un-banned user(s) and looking forward to another great week ahead!
from ScienceBlogs http://ift.tt/2ofbCRF
“There is a fine line between censorship and good taste and moral responsibility.” -Stephen Spielberg
Another week full of amazing science stories has gone by here at Starts With A Bang, and there are some fun and fantastic announcements! We welcomed a new contributor, Jess Shanahan, to our ranks; I found out that Forbes has made me their official Star Trek: Discovery reviewer when that new series premieres; I’m in the process of selecting the final, officially licensed images for my new book, Treknology (and pre-order today!); and from this coming Thursday through Sunday, I’ll be the Science Guest of Honor at NorWesCon in Seattle! Come if you can! Now, let’s take a look back at the past week of articles:
- What’s the difference between a fermion and a boson? (for Ask Ethan),
- Earth prepares to snap first-ever image of a black hole’s event horizon (for Mostly Mute Monday),
- Saturn’s moon Enceladus is our closest great hope for life beyond Earth (by Jess Shanahan),
- How much gold is in the James Webb Space Telescope?,
- ‘Project Blue’ aims to find planets around the nearest sun-like stars, and
- Can muons — which live for just microseconds — save experimental particle physics?
Thanks to our generous Patreon supporters, these articles appear ad-free on Medium one week from their original publication date. And now that it’s time to jump into this edition of our comments of the week, it’s also time to announce that any one-week bans we doled out have now expired. Welcome back to the fold, everyone, and remember to treat each other well!
Perceived knowledge vs. actual knowledge. Image credit: Justin Kruger and David Dunning, 1999.
From Denier on myside bias: “I’m not saying Scientists are bad for being wishy-washy intellectually as new information comes in. I myself am that way. I’m also not saying society is bad for being so tribal as it evolved for a reason. I just find it amusing when academics don’t realize they’ve incorrectly projected a trait where it doesn’t belong.”
I didn’t realize this was what your statement was attempting to convey. Yes, scientists are particularly good — they need to be or they won’t make it — at changing their mind in the face of compelling, overwhelming evidence. The general public is particularly bad at that, and particularly good at choosing sides and defending their side while attacking the opposite side regardless of the quality of the evidence. The further polarization of our society over the past 30 years thanks to the culture wars has arguably made this worse.
I like to think the way out will be evidence-based reasoning. That has proven to be naive so far.
Image credit: Universe Review.
From Michael Mooney on relativity and apparent versus real shapes: “You forget again that a contracted Earth is only “apparent,” i,e., that fast moving frames of reference do not change the physical shape of planets and stars. There is no physics to support shrinking planets and stars.”
On the contrary, Michael, it is only physics that supports a real length contraction. You see, the principle of relativity (and I’m oversimplifying by leaving out caveats here) is that the laws of physics are the same for all observers. If you move fast relative to anything else in the Universe, the laws of physics are the same for you as they are for anyone else. If you see an electron, it has an electric field with a total amount of field energy that’s identical to any other observer.
What happens if you’re at rest vs. in motion with respect to that electron? In order to keep the laws of physics the same, everything about that electron must change in a very particular fashion: its field lines must change, its spatial field density must change, the way a clock runs or distances behave must change, etc. Your measurements, from your perspective, show a real, physical departure from the measurements made aboard the electron, or in the electron’s frame, if you prefer.
The strength of the electric field lines will change in the direction of motion, if the charge is moving relative to you. Image credit: Carel Vandertogt.
That is physics. That is real. That you don’t like it (and/or don’t get it) doesn’t make it untrue.
When you say this: “I have never challenged the “big difference between what people see” in SR. I (and many other SR critics) only challenge the claim that those differences reflect actual physical variations in objects and distances. Yet no SR theorist will admit, “Yes, the differences are only apparent.””
I am puzzled as to what you’re contending. Are you saying that if you switch reference frames, or if you go to the rest frame of the object, then that’s the “true” physical size? That’s nonsense; all reference frames are equally valid. Are you claiming that physical objects aren’t really contracted in their direction of motion? They absolutely are, just like you and I are with respect to an incoming comet. It doesn’t change how we perceive ourselves or the measurements we make, but it’s a real, physical effect that occurs uniquely for every unique observer in the Universe.
Image credit: Fyodor Yurchikhin, of Greenland from the ISS.
From Lee Witt on contesting Denier’s claim that he reasons like a scientist: “Thank you for explaining your repeated refusal to understand the science of climate change – you prefer to believe the fake stories about the gloom and doom that you believe would result from addressing it rather than the mountains of evidence that support the scientists.”
Atmospheric carbon dioxide concentration is presently at a little over 400 parts per million. If fossil fuel emission rates continue at their current values, we will hit 900 parts per million around the year 2300, give or take about 50 years. The increasing CO2 is the primary driver behind the temperature increases on Earth, although the feedback effects are what make it so dire, devastating and inevitable. Cities on Earth are predominantly located in coastal regions or otherwise on the water. A 3 meter sea level rise will submerge about 1.5% of Earth’s current land mass. Melting the Greenland ice sheet will raise sea levels by 8 meters. Melting all the permanent ice on Earth will raise sea levels by more than 30 meters.
You can view this map for yourself and see what sea level rise does to the parts of the Earth you care about. If you truly contend to care about your kids and grandkids, and I believe you, why should I not hold you responsible for your actions and advocacies that damage the lives and livelihoods and destroy the homes and cities of the adults, children and grandchildren of others?
Heat-trapping emissions (greenhouse gases) far outweigh the effects of other drivers acting on Earth’s climate. Source: Hansen et al. 2005, Figure adapted by Union of Concerned Scientists.
From CFT on inexcusable reasoning: “…WHY many scientists don’t agree with the idea of carbon dioxide as being the climatic bogey man…”
Because they selectively ignore evidence. That’s it. There is no good reason for disagreeing with the idea. They ignore large portions of the full suite of evidence. That’s the reason. That might not be your reason or what you hear, but that’s the reason. It is motivated reasoning, plain and simple.
And when someone like Denier says: “No one has a model that perfectly predicts Earth’s atmosphere.”
That is true, but it’s also irrelevant. Yes, climate scientists are wrong in the sense that any science is wrong: there are some predictions that the theory cannot get right, and there are limits to the range of validity of what can be accurately predicted. But if you think that means that all climate science is garbage — or that a denialist model like Curry’s, Lindzen’s, or Easterbrook’s is just as good as the consensus model — then you have failed to understand some very basic principles of science. And remember, the quantitative estimates aren’t estimates that I made up; they are the best estimates I can find by the best scientists working on the problem. If you don’t like them, you are free to “believe” other estimates or come up with your own, but don’t expect anyone else to join you in your belief unless you expect them to abandon expertise (in this case) as you so willingly do.
But if you’re so convinced you’re right, why not go argue with the primary source? Why not become a climate scientist yourself and make sure the field gets it right? Why sit here and argue with an astrophysicist who sees extraordinary competence, scientific integrity and all the hallmarks of it being done right, about the finer points of something when you don’t even accept the coarsest points and the most robust conclusions of all?
The way that atoms link up to form molecules, including organic molecules and biological processes, is only possible because of the Pauli exclusion rule that governs electrons. Image credit: Jenny Mottar.
From John on the difference between fermions and bosons: “What a huge difference a half-integer spin makes!”
Yes! And in particular, what a huge difference obeying or not obeying the Pauli exclusion principle makes. It’s easy to sort of say, “big deal, so I need to put my second fermion somewhere else,” but when you have large numbers of fermions, this gets very impressive (and very important) very quickly.
Pair production and matter-antimatter annihilation. Image credit: Addison-Wesley, retrieved from J. Imamura / U. of Oregon.
From Anonymous Coward on particle/antiparticle collisions: “Colliding a photon with another photon though, under the right conditions, will cause a form of pair production, and it will become an electron-positron pair. What happens when two Z bosons of the weak interaction come together like that?”
Forwards/backwards reactions — or time-symmetric reactions — are the norm in physics. When it comes to the particles in the Universe, if you collide (in general) a particle with its antiparticle counterpart, you can pair-produce any particle/antiparticle pairs for which you have enough energy available, so long as you conserve energy and momentum. There are not major differences in that regard from colliding an electron/positron, quark/antiquark, neutrino/antineutrino, photon/photon, Z-boson/Z-boson, W+ with W-, gluon with its proper gluon counterpart, etc. Cross-sectional differences and the subtle CP-violation of the weak interactions aside, it’s all practically the same.
Michael Kelsey gave even more detail: “Z0 annihilation has not been directly observed (because we can’t make Z0 beams, of course), but the production of Z0 pairs in high energy collisions (at LEP2 and the Tevatron) has been observed. The principle of “detailed balance” means that you can invert that interaction to recognize that a Z-Z collision can produce the accelerator original state. The result should be equivalent to gamma-gamma (or more precisely gamma*-gamma*) interactions, with some pair of particles produced.”
Simulations of how the black hole at the center of the Milky Way may appear to the Event Horizon Telescope, depending on its orientation relative to us. These simulations assume the event horizon exists. Image credit: Imaging an Event Horizon: submm-VLBI of a Super Massive Black Hole, S. Doeleman et al.
From John on testing Einstein’s general relativity: “Directly imaging the event horizon of Sagittarius A* ! How cool is that?!?!?
Even better is the potential to use the Event Horizon Telescope to test EGR”
If General Relativity breaks down anywhere, the physics of black holes is likely the “where” of that. While the physical size of the event horizon (keep reading, Michael Mooney) has some very explicit predictions for it, what we expect to see as the size of the event horizon is quite a bit larger, thanks to the deformation of space in Einstein’s General Relativity. (Which I know is what you meant by EGR, even though everyone else calls it GR.) That 37 microarcseconds is a precise prediction, and if it doesn’t match up by any amount larger than our uncertainty in the black hole’s mass, that could be a very interesting measurement indeed!
Saturn’s E-Ring, as imaged here by Cassini, is created by it’s frozen Moon, Enceladus, ejecting icy material over time. Enceladus is the bright spot at the image’s center. Image credit: NASA/JPL/Space Science Institute.
From Jonathan on Saturn’s E-ring and Enceladus: “so on astronomical time scales, does the loss of matter to Saturn’s E-ring have a noticeable effect on the moon?”
One of the truly fantastic things about Cassini that most people don’t realize is how quantitative it is. Here’s a fun and relevant paper you may enjoy. During an eruption of Enceladus, particles leave the surface vents at a mean rate of about 51 kilograms/second, where 91% eventually fall back to Enceladus and the other 9% go into the ring. The total mass of the E-ring is approximately 1.2 billion kilograms, meaning that the particles live, on average, in the E-ring for only about 8 years. Do they get transferred to other moons or rings? Do they fall back to Enceladus? That Cassini hasn’t measured, but given that Enceladus has a mass of just over 10^20 kg, and that the Solar System is only ~10^17 seconds old, Enceladus still has most of its mass for certain as it did when the Solar System first formed.
Ice fishing here on Earth. Something tells me it would be slightly different on Enceladus. Image credit: Brücke-Osteuropa.
From Sinisa Lazarek on the future news headlines of Enceladus: “Daily News for October 19th 2098
*Breaking News*
– Japenese Orbital Fishing Fleet (JOFF), which recently arrived at Enceladus to begin harvesting native prawns (Penaeus Enceladus) discovers two structures beneath moons thick icy crust. JOFF’s prawn-sonars specially designed to cope with enceladus ice detected what seems to be a US secret military base, some 2 kilometers under the ice. The base seems to be located just below the north polar belt of enceladus. To further their amazement, they also discovered an old USSR submarine under the south polar cap of enceladus. Both locations seem to be long abandoned….”
This is some pretty good science fiction writing here.
A false-color image highlighting Saturn’s hurricane over its north pole, inside the much larger hexagon-shaped feature. Image credit: NASA/JPL-Caltech/SSI.
From Anonymous Coward on the physics of color: “We tend to think of certain wavelengths of light producing certain colours, but if you mix green (495-570 nm) and red (620-740 nm) light we see yellow. Did the mixing of colours cause the light we see to change wavelengths? No. The mixed light excites the M and L cones in our retinas equally, which the brain then interprets as yellow, the same as light in the 570-585 nm wavelength range would. There are even “imaginary colours” that cannot possibly be produced by any physical source of light. The eye has three different types of cones, the S, M, and L cones, and their sensitivities to the various wavelengths of light overlap.”
That’s the whole thing… when we talk about false color vs. true color, we talk about what your eyes can see. And while there’s a lot of physics behind color, there’s also a lot of biology behind color, too! The physics of color is about the wavelength of monochromatic light, or light of a particular wavelength, and that’s it. How our brains interpret it is far more interesting from a “what we see” point of view.
I did write a piece, years ago, answering the question of What Is Color?, if you’re interested, but I caution you that it goes right for the biology in short order, because “color” is inherently a human concept, too.
The 18 segments of James Webb in the laboratory, after completed assembly and all coatings have been applied. The gold is visually striking, but there’s very little of it. Image credit: NASA / Chris Gunn.
From Tomas Ahl on mirrors versus other electronics for James Webb: “To really answer the title question I assume there is more gold than that to make the whole thing? In electronic components, cable connectors etc. Would that accumulate to an equal amount to what is on the mirrors?”
I would also assume that there is lots of gold plating on the various electronic components, to eliminate oxidation yet maintain excellent conductivity while the telescope and instruments are still here on Earth. I sent this question off to a project scientist I know who works for Northrup Grumman, and they didn’t know they answer either. So my guess would be no, because I can’t imagine that the surface area of all the exposed internal wiring is anywhere near what the surface area is for the mirrors themselves, but that’s a guess, not a calculation.
A simulation of what the next Pale Blue Dot would look like through this newly proposed telescope around Alpha Centauri A or B. Image credit: Project Blue Mission Team.
From MobiusKlein on Project Blue for more stars: “For the notion of ‘one shot’, as in there is only one reasonable target to observe given the size of the scope, how much bigger and expensive would it have to be to get useful results from 100 stars?”
This is a good question! If you want to make the measurements Project Blue does for even a third Sun-like star, you need to go up by a factor of 2.5 in diameter: from 45 cm to about 1.3 meters. If you want to get 100 Sun-like stars, you’re talking about going out to about 10 parsecs, which is about 8 times as far as Alpha Centauri A and B. So 8 times a 0.45 meter mirror is about a 4-meter mirror. At present, that would be the largest space telescope ever launched. I would imagine we would be talking in the multi-billion dollar range for a mission like that. Sadly, to get 50 times as many stars would, indeed, be about 50 times as expensive.
Gravitational radiation, illustrated here, clearly occurs along more than one axis. Image credit: ESO / L.Calçada.
From Denier on the number of axes in forces: “We have a 1 axis force that is super long range but wimpy in gravity. Then we have a more powerful but shorter range 2 axis force in electromagnetism. Lastly we have a 3 axis color force that is so powerful it can literally pull matter into existence from nothing but is super short range. There is a weak force but it is really just an offshoot of the 3 axis color force. There is no 4 axis force.”
I’m sorry, but this is not how the fundamental forces work. Gravity is not a one-axis force at all, since it exerts tidal forces, shear forces, and gravitational radiation is a quadrupolar effect. If you want to learn about how the weak, electromagnetic and strong forces work as far as degrees of freedom go, the route you need to go down is group theory. The strong force obeys the rules of the SU(3) group; the electromagnetic obeys the rules of the U(1) group and the weak force obeys the rules of a chiral SU(2) group. Gravitation? Good luck there… whatever group you’re interested in is going to get way bigger than anything with the number “3” in it.
The production of a cosmic ray shower, produced by an incredibly energetic particle from far outside our Solar System. Image credit: Pierre Auger Observatory, via http://ift.tt/11Wasx4.
And finally, from Frank on cosmic ray muons: “How about using natural muons coming from sky?”
The hard problem with muons is collimation, which is why the MICE collaboration’s advances are so important. Cosmic ray muons occur at an approximate rate of one muon per human-hand (about 0.01 square meters) per second. We are looking for bunches of muons at the same energy, the same speed and the same trajectory that are produced in a consistent, controllable fashion. We will someday — for high enough energies — be forced to go back to cosmic rays. But for muons, that day has not arrived just yet!
Thanks for a great week, everyone; welcome back to the un-banned user(s) and looking forward to another great week ahead!
from ScienceBlogs http://ift.tt/2ofbCRF
Aucun commentaire:
Enregistrer un commentaire