Search found 239 matches

by starslayer
Fri May 30, 2014 7:23 pm UTC
Forum: Science
Topic: two black holes and path 'through' 'event horizons'?
Replies: 24
Views: 5419

Re: two black holes and path 'through' 'event horizons'?

It doesn't vanish; instead there exist no real-valued solutions for the location of the event horizon. The actual smallest possible event horizon radius is r_s / 2.
by starslayer
Wed Apr 30, 2014 8:07 pm UTC
Forum: Science
Topic: Singularities & their associated conceptual nastiness
Replies: 35
Views: 5669

Re: Singularities & their associated conceptual nastiness

a) You wanna tell me what interaction mediates intergalactic lensing? Gravity, of course. But light is not generated in lensing; instead, already existing photons have their paths curved by a large local concentration of mass. The existence of gravitational lensing has no relevance to the subject o...
by starslayer
Tue Apr 29, 2014 3:17 pm UTC
Forum: Science
Topic: Singularities & their associated conceptual nastiness
Replies: 35
Views: 5669

Re: Singularities & their associated conceptual nastiness

Colliding black holes do not radiate photons, since they are not significantly charged and therefore do not interact significantly electromagnetically. What they do emit tons of are gravitational waves. The waves emitted by these mergers have a characteristic pattern, and it's this pattern that dete...
by starslayer
Mon Apr 28, 2014 9:48 pm UTC
Forum: Science
Topic: Clarification on event horizons of black holes
Replies: 32
Views: 5188

Re: Clarification on event horizons of black holes

gmalivuk wrote:1.5 times the Schwarzschild radius.

With the specification of unpowered, I think three times the Schwarzschild radius might be more appropriate, since that's the innermost stable circular orbit.
by starslayer
Wed Apr 16, 2014 8:01 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2949
Views: 710157

Re: RELATIVITY QUESTIONS! (and other common queries)

It's about a part in a billion. Over the course of a full year, the person on the surface of the Earth ages about 0.02 seconds less than the guy floating around in deep space.
by starslayer
Mon Apr 14, 2014 2:47 pm UTC
Forum: Science
Topic: Previous Exam Question - Help Requested - Viscousity FLow
Replies: 2
Views: 894

Re: Exam Question - Help Requested - Viscousity FLow

I don't know enough fluid mechanics to help you, however: Is this a take-home exam? From what you've said, it kind of sounds like it. As a general rule, we will not do your homework for you, and we certainly won't help you (or your girlfriend) cheat on an exam. If it's in-class and the test is alrea...
by starslayer
Fri Mar 14, 2014 3:59 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2949
Views: 710157

Re: RELATIVITY QUESTIONS! (and other common queries)

The collapse is going to happen roughly on the scale of the free-fall time, which for a uniform density sphere is sqrt(3*pi/32*G*rho). This situation will probably modify that by a factor of order unity, and certainly by no more than a factor of 10. So, taking 1/sqrt(G*rho) and the density of the Ea...
by starslayer
Wed Dec 11, 2013 4:52 pm UTC
Forum: Science
Topic: Energy equivlence for time of travel: Newton and Einstein
Replies: 20
Views: 4964

Re: Energy equivlence for time of travel: Newton and Einstei

You've rediscovered time dilation , basically. For relativity to be consistent, both a boosted frame's time and space coordinates must change if the speed of light is to be the same for all inertial observers. Of course, the traveler does not see time as slowing down; he would say that his internal ...
by starslayer
Wed Nov 13, 2013 9:40 pm UTC
Forum: Science
Topic: Creationism and the kinetic energy of impact events
Replies: 19
Views: 3896

Re: Creationism and the kinetic energy of impact events

To go back to my admittedly spitballed 10% estimate, even if you assume that 100% of the impact energy goes into heating the body, it still doesn't gain you all that much under my other assumptions. But those assumptions are probably horrible. With a bit of work, you could set up a simple conduction...
by starslayer
Wed Nov 13, 2013 9:24 pm UTC
Forum: Science
Topic: Tidal deformation of a moon
Replies: 22
Views: 4515

Re: Tidal deformation of a moon

Kepler's 3rd Law says that P2 = 4pi2R3/G(M+m), so I get a period of 1.3 hours. Shark Week doesn't violate lightspeed, but it comes within a factor of three. Usually a bad sign when talking about orbits of non-degenerate bodies.
by starslayer
Fri Nov 08, 2013 6:03 pm UTC
Forum: Science
Topic: Chemistry: Help requested with mineral citrates
Replies: 4
Views: 2346

Re: Chemistry: Help requested with mineral citrates

We did. But looking at the Wiki pages for both chemicals, both are called magnesium citrate, so the company wasn't lying. It just isn't magnesium citrate (1:1), but rather is magnesium citrate (3:2), which according to Wiki tastes bitter and is not very soluble in water. The tests the OP has already...
by starslayer
Fri Nov 08, 2013 5:57 pm UTC
Forum: Science
Topic: Creationism and the kinetic energy of impact events
Replies: 19
Views: 3896

Re: Creationism and the kinetic energy of impact events

So, thinking about this a bit more extensively, and taking into account Schrollini's point that we really only care about the impact basins, here's what I've got. The largest basin on the Moon, by far, is the South-Pole Aitken basin, at 2,500 km wide. Using the same assumptions I outlined in my firs...
by starslayer
Thu Nov 07, 2013 10:07 pm UTC
Forum: Science
Topic: Tidal deformation of a moon
Replies: 22
Views: 4515

Re: Tidal deformation of a moon

You're not having much luck because that problem is really fucking hard. I don't know of any quick way to estimate it, unfortunately. You might have to start checking out graduate dynamics textbooks, doing an ADS search, or looking up stuff in some of the physics journals.
by starslayer
Thu Nov 07, 2013 9:56 pm UTC
Forum: Science
Topic: Creationism and the kinetic energy of impact events
Replies: 19
Views: 3896

Re: Creationism and the kinetic energy of impact events

That should be fine. Here's how I would proceed further though: A database of all visible lunar craters and their radii does not, to my knowledge, exist. Some people have made attempts at doing this down to certain diameters (like this guy ), and come up with estimates of the number of craters with ...
by starslayer
Fri Oct 25, 2013 4:06 pm UTC
Forum: Science
Topic: Lower bound for Earthlike planet
Replies: 40
Views: 7007

Re: Lower bound for Earthlike planet

Partially. The Earth already went through differentiation like that. Elements do sort of get sorted by density (all the iron is at the center of the Earth, after all!), but they also get sorted chemically. For example, uranium bonds readily to oxygen, so it is more common in the Earth's crust than y...
by starslayer
Sun Oct 20, 2013 10:07 pm UTC
Forum: Science
Topic: Lower bound for Earthlike planet
Replies: 40
Views: 7007

Re: Lower bound for Earthlike planet

Surely the two are related? Can a planet have high escape velocity but low surface gravity? Yes. Look at Saturn. Hardly really applicable then given we're not talking about gas giants? I'm still uncertain though how that works? Is the high escape velocity due to atmospheric drag getting off Saturns...
by starslayer
Sun Oct 06, 2013 8:21 pm UTC
Forum: Science
Topic: electron degeneracy, neutron degeneracy, and pressure?
Replies: 11
Views: 4385

Re: electron degeneracy, neutron degeneracy, and pressure?

Yeah, we don't know the nuclear matter equation of state yet. It's one of the big unknowns in neutron star physics, and it almost certainly does not have an analytic form. People have been doing/trying to do numerical simulations of it for 30-40 years now, but still haven't had definitive success. a...
by starslayer
Wed Oct 02, 2013 7:30 pm UTC
Forum: Science
Topic: Size limit for rocky planets
Replies: 18
Views: 4427

Re: Size limit for rocky planets

Are there any realistic conditions where a rocky planet of, say, 5 Jupiter masses could naturally form in the first place? Planetary formation happens in the accretion disc of a protostar, which, to my understanding, is chiefly made of hydrogen, helium, and traces of the heavier rocky stuff. If a s...
by starslayer
Mon Sep 30, 2013 12:52 am UTC
Forum: Science
Topic: Do we have a way to watch out for Gamma Ray Bursts?
Replies: 6
Views: 2232

Re: Do we have a way to watch out for Gamma Ray Bursts?

The hazard isn't the atmosphere being blown off; the article correctly described it as the gamma rays catalyzing the formation of an enormous nitrous oxide smog layer. Nitrous oxides destroy ozone. They would fall out of the atmosphere over the next several years, but with no ozone, the UV flux on t...
by starslayer
Tue Sep 03, 2013 7:14 pm UTC
Forum: Science
Topic: Shape of the big bang
Replies: 6
Views: 2198

Re: Shape of the big bang

Yes, you could put it on a log-log scale. Then you just get two straight lines with slopes of 1/2 (radiation-dominated phase) and 2/3 (matter-dominated), followed by exponential growth (dark energy/cosmological constant dominated). Only question is which ages you put the break points at. But on a lo...
by starslayer
Sat Aug 17, 2013 7:47 pm UTC
Forum: Science
Topic: Amplitude in metres
Replies: 12
Views: 5363

Re: Amplitude in metres

There are different types of light waves just as there are different types of waves in a solid (compression vs transverse.) Light is always a transverse wave. The electromagnetic field cannot support longitudinal oscillations. Yeah, I found this confusing, too. The electric and magnetic fields are ...
by starslayer
Thu Jun 06, 2013 10:09 pm UTC
Forum: Science
Topic: Size of the observeable universe
Replies: 31
Views: 8937

Re: Size of the observeable universe

doogly was responding to what you called "handwavy": Of course most cosmologies today have space expanding with matter, rather than matter expanding within space, but it's quite handwavey why that should be so. GR requires the metric expansion or contraction of space if the Cosmological Pr...
by starslayer
Thu Jun 06, 2013 6:14 pm UTC
Forum: Science
Topic: Help me study physics please?
Replies: 8
Views: 4444

Re: Help me study physics please?

For part c, I'd start with geometry. You know it's taken 2 seconds to go 30 degrees around the circle. From this you can get how long it takes to go around the entire circle, and from that you know the radius.
by starslayer
Tue Jun 04, 2013 3:02 pm UTC
Forum: Science
Topic: Global Warming Mitigation
Replies: 15
Views: 5448

Re: Global Warming Mitigation

How high do envision the chimney being? The scale height of the atmosphere is about 10 km, and you aren't going to build a tower anywhere near that tall. Anything much less than that really won't do anything, since you aren't getting above a significant portion of the atmosphere. I really don't see ...
by starslayer
Fri May 31, 2013 10:15 pm UTC
Forum: Science
Topic: Space telescope for private use
Replies: 11
Views: 5164

Re: Space telescope for private use

HH47 is visible in I band at least (roughly 13.5 mag); it is ~1-2 arcminutes in size, so you should get some detail. Hannys Voorwerp is probably invisible because it is simply too faint, but it's more than big enough to be resolved. You could see the host galaxy, IC 2479, though. It's roughly a 15th...
by starslayer
Fri May 31, 2013 4:21 pm UTC
Forum: Science
Topic: Space telescope for private use
Replies: 11
Views: 5164

Re: Space teleskope for private use

Off the top of my head, I'd be willing to bet on the space-based one being vastly superior. Hubble can outperform an >8m telescope unless the ground-based one is using adaptive optics (which all of the largest ones do, but I doubt you'd be able to find a 30cm one with adaptive optics). With adaptiv...
by starslayer
Fri May 17, 2013 5:44 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2949
Views: 710157

Re: RELATIVITY QUESTIONS! (and other common queries)

Correction time! I quoted a temperature for the CNB of 2.95 K, which is incorrect, as the paper doogly posted helpfully points out. The temperature is actually 1.95 K if the neutrinos have remained relativistic until today. Since they are massive and probably aren't relativistic, you need to add an ...
by starslayer
Fri May 17, 2013 3:31 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2949
Views: 710157

Re: RELATIVITY QUESTIONS! (and other common queries)

I will assume we are discussing electron neutrinos, and that they have a mass of 1 eV (I think that's consistent with current measurements). This is much larger than their kinetic energy, so the CNB neutrinos are now highly non-relativistic. Their speed is then roughly 2% the speed of light, or ~7E...
by starslayer
Wed May 15, 2013 4:06 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2949
Views: 710157

Re: RELATIVITY QUESTIONS! (and other common queries)

I have a quick question about the cosmic neutrino background. According to http://en.wikipedia.org/wiki/Redshift#Highest_redshifts Other high-redshift events predicted by physics but not presently observable are the cosmic neutrino background from about two seconds after the Big Bang (and a redshif...
by starslayer
Tue Apr 09, 2013 12:33 am UTC
Forum: Science
Topic: Blowing up the Earth more efficiently
Replies: 41
Views: 9174

Re: Blowing up the Earth more efficiently

Wow, you did your homework. But where is this radiative cooling going to go? We're assuming this is several hundred miles underground. Isn't the energy from the radiative cooling going to go straight into the surrounding mantle....which is precisely where we need it to go? If we can set up the init...
by starslayer
Mon Apr 08, 2013 8:42 pm UTC
Forum: Science
Topic: Blowing up the Earth more efficiently
Replies: 41
Views: 9174

Re: Blowing up the Earth more efficiently

Ok, so I thought a little but more about this, and came to the conclusion that this is unfeasible in the extreme due to cooling. Take the most favorable case imaginable: you have a 100 km sphere (so cooling is less efficient) that you instantly convert to 3 billion K plasma and is half oxygen by mas...
by starslayer
Fri Apr 05, 2013 8:14 pm UTC
Forum: Science
Topic: Blowing up the Earth more efficiently
Replies: 41
Views: 9174

Re: Blowing up the Earth more efficiently

Fusion requires extremely high temperatures and confinement. Runaway/chain-reaction fusion requires degenerate matter or an outside confining force. In the case of the Earth, the only confining force you have is gravity unless you provide one yourself. Making one will take an inordinate amount of en...
by starslayer
Fri Mar 22, 2013 6:18 pm UTC
Forum: Science
Topic: Sun's Energy Production Per Cubic Meter
Replies: 17
Views: 5884

Re: Sun's Energy Production Per Cubic Meter

No, the Sun is dominated by p-p fusion. CNO fusion does not become the main energy source until stars hit about 1.5 M_sun (See Figure 22.6 in Kippenhahn & Weigert). The reason is that CNO fusion goes as T 16 , while p-p fusion goes as T 4 at the relevant temperatures. The reason it's hypothesize...
by starslayer
Tue Mar 19, 2013 7:01 pm UTC
Forum: Science
Topic: Neat and tidy charges - An unanswered question or not?
Replies: 27
Views: 5534

Re: Neat and tidy charges - An unanswered question or not?

idobox wrote:Are there experiments trying to measure the charge of the electron and proton?
Yes; NIST does this for lots of physical constants from time to time. However, measurements of the elementary charge are not new; the charge of the electron was first measured in 1909.
by starslayer
Tue Mar 19, 2013 6:54 pm UTC
Forum: Science
Topic: Sun's Energy Production Per Cubic Meter
Replies: 17
Views: 5884

Re: Sun's Energy Production Per Cubic Meter

The initial concentration of Helium was not 0, and the sun will transform and die before all the hydrogen is gone. From what I understand, the heavier helium stays at the centre, replacing hydrogen, and slowly diminishing power production. At some point, the core will be too cold to sustain fusion,...
by starslayer
Mon Mar 18, 2013 6:04 pm UTC
Forum: Science
Topic: Question about capacitors and energy conversion.
Replies: 2
Views: 990

Re: Question about capacitors and energy conversion.

1: The air resistance force matters here, but is smaller than you think. The drag force for high Reynolds number (in this case, R ~ 55,000 >> 1) is 1/2*rho*C d *A*v 2 , where rho is the fluid density, A is cross sectional area, C_d is the drag coefficient, and v is the object's velocity. Assuming A ...
by starslayer
Mon Mar 18, 2013 2:19 pm UTC
Forum: Science
Topic: Sun's Energy Production Per Cubic Meter
Replies: 17
Views: 5884

Re: Sun's Energy Production Per Cubic Meter

Hmmm. IIRC, some experimental fusion reactors outclass the heat and pressure of the sun's core. I am getting worried about what it is going to take to make a CNO cycle fusion reactor. Heat, maybe, but not pressure (unless we suddenly achieved 25,000 TPa while I wasn't looking). You also wouldn't wa...
by starslayer
Fri Feb 15, 2013 7:33 pm UTC
Forum: Science
Topic: Why do some people believe the universe is infinite?
Replies: 91
Views: 14428

Re: Why do some people believe the universe is infinite?

If it is flat or open (the two most likely possibilities, given the current results from WMAP, Ia SNe, and baryon acoustic oscillations), then the universe is infinite and has always been so. Those three each have rather large wikipedia pages. Could someone please give a small explanation of why th...
by starslayer
Fri Feb 15, 2013 7:14 pm UTC
Forum: News & Articles
Topic: Meteor attack in Russia
Replies: 92
Views: 13782

Re: Meteor attack in Russia

As far as I know, it's not even possible to intercept ICMBs because they go too fast. And a meteor makes those look slow. It's perfectly possible to intercept ICBMs and their warheads. Both Russia and the US developed those systems in the 60s and 70s. What really helps there is that you have plenty...
by starslayer
Wed Feb 06, 2013 3:21 am UTC
Forum: Food
Topic: The Liquor Thread
Replies: 1265
Views: 276490

Re: The Liquor Thread

So I picked up a bottle of Booker's, and while it is delicious, I can't help but wonder how amazing it would taste as a Manhattan or Old Fashioned. Then I feel bad for wanting to mix a $60 bourbon. Has anyone here tried it in a cocktail? A little late, but I just bought a bottle of Booker's as well...

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