...The author pays a bit over $100 a page for the major US journals. You budget for it in your grants. Still, we have subscriptions at huge cost, despite very common free preprint servers. My colleagues in many other fields don't pay, and the universities do. Yes, I agree there should be a better model.
I'm the director of graduate admissions to a physics and astronomy department. It's small numbers compared to HBS, but it's probably similarly vitally important to applicants. Hell, I usually tell applicants straight up what's going on with their applications. There's none of this stupid deciding, posting, and then getting pissed if they find out early. WTF are these people thinking?! Harvard people in this instance are amazing assholes. At best for them it is entrapment. At best. Fucking tell applicants if they're in or out, and leave out this bullshit web system that is messing with them. Harvard absolutely sucks here, and I think their applicant pool should drop accordingly. They are being unethical here. Screw their applicants -- I'm not going to try to read their minds about a simple URL redirection. HARVARD has fucked up and needs to own up to it and apologize.
Let's go one further. Harvard fucked up twice here. They apparently made their decisions a month early and didn't share them in a timely manner. Perhaps there are good reasons for that, perhaps not. But they also used an insecure system. I mean, if they left a list posted in a closet somewhere, and people found out about it, who is to blame? The people who look, or the person who put the list in the closet? I think Harvard is going on the offensive here to cover up their own error, and I think it kind of sucks.
I think so, too, if it's good. This is why I have my novel Star Dragon available for free download at http://www.mikebrotherton.com as advertised. I think it's good, and the downside of giving away free copies will be more than balanced by the extra publicity which, with luck, will translate into more paperback sales. It least that's the gamble Tor and I are making.
You're mistaken about the dearth of comets. We observe well over 50 new comets each YEAR since the era of modern astronomy. For designated comets in the past decade, please see the compilation for instance.
The Oort cloud existence is on very solid footing. The numbers I'm aware of are 50-500 Earth masses, and since this is less than 1/1000 of a solar mass spread out over a huge volume, in discrete chunks, we can certainly address the probability of hitting something flying a space ship through it (which was the original question).
Some issues you mention or allude to, like inner Oort clouds, Kuiper belts, etc., are important for understanding the details and placing constraints on the masses invovled to better than an order of magnitude, but an order of magnitude isn't relevant to the question at hand. And hey, an order of magnitude seems pretty good to me. Astronomy is hard!
That's right. There's just not much stuff out there. The chances would be tiny.
The one caveat to this concerns the speed of the spaceship. If it approaches relativistic speeds, a pebble can hit like a mountain. In this situation, you'd want to have some kind of active shielding. I describe one such system in my novel Star Dragon, which is out in paperback or available from my website for free download.
Basically correct. Yes, the stars emit light. All the visible light gets repeatedly scattered by the dust, heating it, and it in turn warms up some and radiates in the mid-to-far infrared. Spitzer looks in the mid-infrared with the instrument used in this study and spotted the galaxies at locations where we see nothing at optical wavlengths. We know they're galaxies because they are so far away but bright enough to detect, their instrinsic luminosity is huge (galaxy level).
The hot intercluster medium IS hot, but temperture is a funny thing in some astronomical settings. In this case, the density of particles is so low, a better vacuum than you'd get in Earth laboratories, that the heat content would be pretty low. You wouldn't get incinerated, for instance. But a conventional thermometer wouldn't work either since it probably wouldn't get into thermodynamic equilibrium. It would radiate away its heat faster than the ambient gas could warm it.
Astronomers have excellent limits on the amount of normal matter, as the parent poster says. We've got an excellent idea what is out there based on emission in the far infrared, interstellar scintillation, absorption line studies, reddening studies, etc. We have very good limits on the Oort cloud density, too, from comet statistics. There are even a number of direct observations based on microlensing surveys, and there's a shadow survey, too, looking at large star fields. In short, we've got pretty good numbers and we're not going to discover that there's more normal dark baryonic matter out there than we already know about.
Even among astronomers, nomenclature gets sloppy. I often refer to observations done at 800 or 900 nm as "visible" because we use the same detectors. Light at those wavelengths is almost impossible to actually see. To me, the infrared starts at 1 micron, because that's where you'd switch and use a different instrument with a different dector. The bandgap for silicon corresponds to 1.1 microns, and somewhere close to 1 micron the response falls very low.
You can see what I mean if you have certain types of black and white digital cameras. You can take a picture and see your infrared TV remote light (940 nm) quite clearly.
Because these galaxies are surrounded by dust (likely from massive starbursts, which produce dust). Dust, because of it's scattering properties, preferentially lets long wavelength light pass through it (ie. infrared) but scatters shorter wavelength light (ie. visible light) into other directions. This is the same effect you see when looking at a sunset. The setting sun looks redder because there is dust (small, scattering particles of various sorts) letting more red light through to you than blue light. In these galaxies, it is more extreme.
The effect is called "dust reddening." I have some slides about it for the lastest entry (March 2) for my Astronomy 1050 class at my astronomy webpage if you want to see examples.
There are presumably stars in there, mostly obscured by dust. And likely quasars/actic galactic nuclei. Admittedly, there is speculation here, but educated speculation. What is known is the redshift, the energy flux, which together give us the distance and luminosity. The luminosities are huge -- only galaxies have such huge luminosities. Only massive starbursts or quasars could power these objects. Quasars seem to exist only in the centers of massive galaxies. Ergo, we must have galaxies filled with stars. Also, the dust redenning means there's a lot of dust present, and it takes certain kinds of stars to make dust. Ergo, there are a lot of stars there.
As I said, speculation, but educated speculation. Not a big leap of faith in the arguments above.
That's because you're not an astronomy professor. Radio waves are light, and no one should give me a funny look about it, especially during lecture. Hammering in a basic point like this helps students remember that radio waves travel at the speed of light (NOT SOUND! Oh I see that a lot), suffer diffraction like other wavelengths of light, etc. Of course, I then make a big point of saying how visible light is just EM radiation.
Re:Another nutshell review
on
Exultant
·
· Score: 2, Interesting
Since it has been suggested elsewhere in the thread that science fiction is only appropriate until you're fifteen or so, I thought I should sink to that level.
Stephen Baxter is amongst the hardest of the hard sci-fi writers.
I'm harder.
Re:This only shows how poorly you have read...
on
Exultant
·
· Score: 3, Insightful
Then try reading some more, or keep your snobbery to yourself. Why not tell everyone what you think is so perfect and wonderful for those aged 16+? Then you can get some/. snobbery back (and I have no doubt equally passionate and honest snobbery) about how your particular choice isn't so great. I read inside and outside the genre, and while I would hope bright 15 year olds would enjoy my science fiction novels, I would also hope 16 year olds would.
There are ideas -- deep, important ideas -- to explore about what it means to be human that can't be done in mainstream literature. Now, science fiction can be bad, but so can any literary form. It can also be great. Again, you could try reading some more. Don't limit yourself to the "major" sf books/series which are more likely to reach for the lowest common denominator to reach a broader audience. Look especially at Nebula Award winners, which are chosen by other writers, not the fans (although Nebula politics can skew results).
Have you read Stand on Zanzibar by John Brunner? How about Replay by Ken Grimwood? The Stars My Destination by Alfred Bester?
At least you could keep quiet. It's pretty rude to wade into a conversation people are having only to proclaim that they're talking about something only kids should like.
I did this once with a fire alarm in high school. I thought it might be broken (seriously). It wasn't. I got off the hook since with my reputation they believed me.
I'm also reminded of an old Dr. Who episode with the Daleks. The Doctor asks Davros, creator of the Daleks, if he would really press such a button given the choice. Davros comes back with something like, "To have that kind of power...and not use it? Yes, yes, I believe I would."
Very good, classic book, by David Gerrold (who shows up here on/. from time to time). I think the vocal minority who hate it just get turned off by this element (although stylistically I can see the book rubbing some readers the wrong way, too).
I've read his first, Revelation Space, which I liked, although it took me some time to get into it. He's the only professional astronomer I know other than myself currently publishing sf novels. Physicists, yes, piles of them it seems, but not so many astronomers.
Just because something is hard sf doesn't mean it's badly written or whatever. You don't like Forward, ok, try a Baxter book or some other (with or without "Dragon" in the title). I'm partial to Vernor Vinge, Joe Haldeman, Greg Egan, and Jack McDevitt myself.
I'm a novelist, and my work has been nominated for ALA awards in the past. I think there's something to be said for the point of view that blog writing is not as complex as what is found in most published books. On the other hand, I think this is overlooking the value of blogs. Blogs are not meant to be, usually, examples of sophisticated writing, and people who like blogs to read/write, may also like most sophisticated works. It is NOT an either/or. I blog on my webpage in an effort to be accessible to interested readers of my work, and potential readers, by providing insight into my writing an my life as a scientist. My goal in blogging is not the same as it is with my novels, and I don't see a problem with that. We need a diversity in writing the same way we need diversity in all artistic expression. Limmericks and haiku are not as sophisticated as sonnets as sestinas, but that doesn't make them bad.
Prior to recombination, the photons are repeatedly scattered by the plasma. I "misspoke" about coupling of the baryons to the plasma -- I meant to say that the photons are coupled to the baryon plasma. They share energy/momentum and directly affect each other. The photons do not interact with the non-baryonic matter which is transparent to them, and so they are uncoupled, and the non-baryonic material will not have a significant effect. Sorry for not being clearer before.
Sorry, my off-the-cuff statement about the sound speed and baryon density wasn't really right. Certainly there is some effect there, but it isn't the important issue in determining the amplitude of the second peak. I teach this stuff, but I don't do research in it and I do need to look up the details sometimes.
The descreased amplitude of the second peak arises from an effect called baryon loading explained here. The suppression arises from a coupling of the barynons to the plasma prior to recombination. The non-baryonic matter is transparent.
Slashdot Mirror
...The author pays a bit over $100 a page for the major US journals. You budget for it in your grants. Still, we have subscriptions at huge cost, despite very common free preprint servers. My colleagues in many other fields don't pay, and the universities do. Yes, I agree there should be a better model.
So Harvard actually wouldn't have admitted any of the 119 in the first place, making this whole discussion moot, right? Wait...
Here here!
I'm the director of graduate admissions to a physics and astronomy department. It's small numbers compared to HBS, but it's probably similarly vitally important to applicants. Hell, I usually tell applicants straight up what's going on with their applications. There's none of this stupid deciding, posting, and then getting pissed if they find out early. WTF are these people thinking?! Harvard people in this instance are amazing assholes. At best for them it is entrapment. At best. Fucking tell applicants if they're in or out, and leave out this bullshit web system that is messing with them. Harvard absolutely sucks here, and I think their applicant pool should drop accordingly. They are being unethical here. Screw their applicants -- I'm not going to try to read their minds about a simple URL redirection. HARVARD has fucked up and needs to own up to it and apologize.
Let's go one further. Harvard fucked up twice here. They apparently made their decisions a month early and didn't share them in a timely manner. Perhaps there are good reasons for that, perhaps not. But they also used an insecure system. I mean, if they left a list posted in a closet somewhere, and people found out about it, who is to blame? The people who look, or the person who put the list in the closet? I think Harvard is going on the offensive here to cover up their own error, and I think it kind of sucks.
I think so, too, if it's good. This is why I have my novel Star Dragon available for free download at http://www.mikebrotherton.com as advertised. I think it's good, and the downside of giving away free copies will be more than balanced by the extra publicity which, with luck, will translate into more paperback sales. It least that's the gamble Tor and I are making.
You're mistaken about the dearth of comets. We observe well over 50 new comets each YEAR since the era of modern astronomy. For designated comets in the past decade, please see the compilation for instance.
The Oort cloud existence is on very solid footing. The numbers I'm aware of are 50-500 Earth masses, and since this is less than 1/1000 of a solar mass spread out over a huge volume, in discrete chunks, we can certainly address the probability of hitting something flying a space ship through it (which was the original question).
Some issues you mention or allude to, like inner Oort clouds, Kuiper belts, etc., are important for understanding the details and placing constraints on the masses invovled to better than an order of magnitude, but an order of magnitude isn't relevant to the question at hand. And hey, an order of magnitude seems pretty good to me. Astronomy is hard!
That's right. There's just not much stuff out there. The chances would be tiny.
The one caveat to this concerns the speed of the spaceship. If it approaches relativistic speeds, a pebble can hit like a mountain. In this situation, you'd want to have some kind of active shielding. I describe one such system in my novel Star Dragon, which is out in paperback or available from my website for free download.
Basically correct. Yes, the stars emit light. All the visible light gets repeatedly scattered by the dust, heating it, and it in turn warms up some and radiates in the mid-to-far infrared. Spitzer looks in the mid-infrared with the instrument used in this study and spotted the galaxies at locations where we see nothing at optical wavlengths. We know they're galaxies because they are so far away but bright enough to detect, their instrinsic luminosity is huge (galaxy level).
I'll just reply to a few of the questions raised.
The hot intercluster medium IS hot, but temperture is a funny thing in some astronomical settings. In this case, the density of particles is so low, a better vacuum than you'd get in Earth laboratories, that the heat content would be pretty low. You wouldn't get incinerated, for instance. But a conventional thermometer wouldn't work either since it probably wouldn't get into thermodynamic equilibrium. It would radiate away its heat faster than the ambient gas could warm it.
Astronomers have excellent limits on the amount of normal matter, as the parent poster says. We've got an excellent idea what is out there based on emission in the far infrared, interstellar scintillation, absorption line studies, reddening studies, etc. We have very good limits on the Oort cloud density, too, from comet statistics. There are even a number of direct observations based on microlensing surveys, and there's a shadow survey, too, looking at large star fields. In short, we've got pretty good numbers and we're not going to discover that there's more normal dark baryonic matter out there than we already know about.
Even among astronomers, nomenclature gets sloppy. I often refer to observations done at 800 or 900 nm as "visible" because we use the same detectors. Light at those wavelengths is almost impossible to actually see. To me, the infrared starts at 1 micron, because that's where you'd switch and use a different instrument with a different dector. The bandgap for silicon corresponds to 1.1 microns, and somewhere close to 1 micron the response falls very low.
You can see what I mean if you have certain types of black and white digital cameras. You can take a picture and see your infrared TV remote light (940 nm) quite clearly.
In particular, you'd want to look at the slide for "Dark Nebula" if you go looking for this.
Yes, that would appear to be it. Mod parent up.
Because these galaxies are surrounded by dust (likely from massive starbursts, which produce dust). Dust, because of it's scattering properties, preferentially lets long wavelength light pass through it (ie. infrared) but scatters shorter wavelength light (ie. visible light) into other directions. This is the same effect you see when looking at a sunset. The setting sun looks redder because there is dust (small, scattering particles of various sorts) letting more red light through to you than blue light. In these galaxies, it is more extreme.
The effect is called "dust reddening." I have some slides about it for the lastest entry (March 2) for my Astronomy 1050 class at my astronomy webpage if you want to see examples.
There are presumably stars in there, mostly obscured by dust. And likely quasars/actic galactic nuclei. Admittedly, there is speculation here, but educated speculation. What is known is the redshift, the energy flux, which together give us the distance and luminosity. The luminosities are huge -- only galaxies have such huge luminosities. Only massive starbursts or quasars could power these objects. Quasars seem to exist only in the centers of massive galaxies. Ergo, we must have galaxies filled with stars. Also, the dust redenning means there's a lot of dust present, and it takes certain kinds of stars to make dust. Ergo, there are a lot of stars there.
As I said, speculation, but educated speculation. Not a big leap of faith in the arguments above.
That's because you're not an astronomy professor. Radio waves are light, and no one should give me a funny look about it, especially during lecture. Hammering in a basic point like this helps students remember that radio waves travel at the speed of light (NOT SOUND! Oh I see that a lot), suffer diffraction like other wavelengths of light, etc. Of course, I then make a big point of saying how visible light is just EM radiation.
Since it has been suggested elsewhere in the thread that science fiction is only appropriate until you're fifteen or so, I thought I should sink to that level.
Stephen Baxter is amongst the hardest of the hard sci-fi writers.
I'm harder.
Then try reading some more, or keep your snobbery to yourself. Why not tell everyone what you think is so perfect and wonderful for those aged 16+? Then you can get some /. snobbery back (and I have no doubt equally passionate and honest snobbery) about how your particular choice isn't so great. I read inside and outside the genre, and while I would hope bright 15 year olds would enjoy my science fiction novels, I would also hope 16 year olds would.
There are ideas -- deep, important ideas -- to explore about what it means to be human that can't be done in mainstream literature. Now, science fiction can be bad, but so can any literary form. It can also be great. Again, you could try reading some more. Don't limit yourself to the "major" sf books/series which are more likely to reach for the lowest common denominator to reach a broader audience. Look especially at Nebula Award winners, which are chosen by other writers, not the fans (although Nebula politics can skew results).
Have you read Stand on Zanzibar by John Brunner? How about Replay by Ken Grimwood? The Stars My Destination by Alfred Bester?
At least you could keep quiet. It's pretty rude to wade into a conversation people are having only to proclaim that they're talking about something only kids should like.
I did this once with a fire alarm in high school. I thought it might be broken (seriously). It wasn't. I got off the hook since with my reputation they believed me.
I'm also reminded of an old Dr. Who episode with the Daleks. The Doctor asks Davros, creator of the Daleks, if he would really press such a button given the choice. Davros comes back with something like, "To have that kind of power...and not use it? Yes, yes, I believe I would."
Very good, classic book, by David Gerrold (who shows up here on /. from time to time). I think the vocal minority who hate it just get turned off by this element (although stylistically I can see the book rubbing some readers the wrong way, too).
I've read his first, Revelation Space, which I liked, although it took me some time to get into it. He's the only professional astronomer I know other than myself currently publishing sf novels. Physicists, yes, piles of them it seems, but not so many astronomers.
Just because something is hard sf doesn't mean it's badly written or whatever. You don't like Forward, ok, try a Baxter book or some other (with or without "Dragon" in the title). I'm partial to Vernor Vinge, Joe Haldeman, Greg Egan, and Jack McDevitt myself.
I'm a novelist, and my work has been nominated for ALA awards in the past. I think there's something to be said for the point of view that blog writing is not as complex as what is found in most published books. On the other hand, I think this is overlooking the value of blogs. Blogs are not meant to be, usually, examples of sophisticated writing, and people who like blogs to read/write, may also like most sophisticated works. It is NOT an either/or. I blog on my webpage in an effort to be accessible to interested readers of my work, and potential readers, by providing insight into my writing an my life as a scientist. My goal in blogging is not the same as it is with my novels, and I don't see a problem with that. We need a diversity in writing the same way we need diversity in all artistic expression. Limmericks and haiku are not as sophisticated as sonnets as sestinas, but that doesn't make them bad.
Prior to recombination, the photons are repeatedly scattered by the plasma. I "misspoke" about coupling of the baryons to the plasma -- I meant to say that the photons are coupled to the baryon plasma. They share energy/momentum and directly affect each other. The photons do not interact with the non-baryonic matter which is transparent to them, and so they are uncoupled, and the non-baryonic material will not have a significant effect. Sorry for not being clearer before.
Sorry, my off-the-cuff statement about the sound speed and baryon density wasn't really right. Certainly there is some effect there, but it isn't the important issue in determining the amplitude of the second peak. I teach this stuff, but I don't do research in it and I do need to look up the details sometimes.
The descreased amplitude of the second peak arises from an effect called baryon loading explained here. The suppression arises from a coupling of the barynons to the plasma prior to recombination. The non-baryonic matter is transparent.