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Italy12246 Posts
On April 25 2015 05:56 Sn0_Man wrote:
The most interesting thing to me in all of physics (okay i guess this is kinda only tangentially related but still) is why there is no good quantum theory of gravity
Mostly a combination of a) the math to write it either doesnt exist, or isn't well understood b) it's such a clusterfuck that every theory of quantized gravity hasn't produced any experimental prediction that can be verified with current technology
On April 25 2015 06:02 FiWiFaKi wrote:Show nested quote +On April 25 2015 05:04 Teoita wrote:
Yeah i am, i'm getting my master's and i want to pursue it as a career Who hires an astrophysicist? I mean, what you know is great, but is there anyone in the public sector that desires this kind of knowledge about the universe? If all of the sudden everyone in the world forgot how everything functions beyond our solar system, I don't think much would change for anyone's life (minus the astrophysicist, pardon me, I'm a mechanical engineer). Anyway, seems mostly the government bodies of NASA or large EU programs, and universities, etc.
I have pretty much the same preparation as a physicist as far as problem solving goes, so if i didn't want to do research i would have the same opportunities. For research, you pretty much work at a university, if you're good there's good jobs. It's a very hard field for sure, but i'm confident i can make it.
Besides, while immediate knowledge may not help, technological progress is pushed by basic research like astrophysics. In fact, the CCD's in digital cameras and phones for example are a byproduct of the need for better relevators for optical photons in telescopes, just to make an example.
Regarding the four basic forces, you are confusing a basic force with a scalar field. A scalar field that may or may not be quantized is simply an interaction between two objects, that behaves in a particular mathematical way. It doesn't have to be one of the basic forces, all inflation is saying is "look if in the universe there was a potential of some kind with those properties, then that can produce inflation". What that potential actually is - in quantum mechanical term, what an eventual quantum of that field, called inflaton in this case - or what its properties are, is an even more advanced topic; i attended a seminar about the theoretical side of it when BICEP2 announced they had detected proof of inflation and frankly i didn't understand a word after the first couple of slides.
To this day, the only quantized scalar field outside of the four basic forces that has been shown to exist through experiments is the Higgs field, along with the Higgs boson, but it's as far as theoretical physics goes it's a very convenient way to describe a certain phenomenon. I personally deal with lots of scalar fields when i study the gravitational field inside a galaxy - that's just a particular kind of gravitational field, without any fancy quantums or whatever necessary. The "language" used is still that of a scalar field.
Regarding "the way to make the universe work", there's actually not just one.
The most accepted is the lambda cdm model i discussed earlier - which is essentially applied general relativity, in which you have about 70% of the mass-energy density of the universe in dark energy (which we have no idea wtf it is), roughtly 30% in mass, and 25% of that is dark matter which is only slightly less mysterious, and only a minuscle fraction is in radiation.
Some people instead believe the correct way to look at things is to modify gravity completely, adding on a few pieces to general relativity, but i personally dislike that explanation because it starts from the premise of "wtf we need to find some way to make dark energy and dark matter disappear since we dont know wtf it is", and it ends up being overly complex, and not explaining data very well at that.
I'm not sure what you mean by "loss of information principle", but mathematically speaking, solving what is called the N-body problem (ie, an arbitrary number of objects interacting through gravity) isn't possible (to our knowledge) without some underlying assumptions and semplifications, and even then you need to use a really, really powerful calculator to do that; but i guess yeah, if you have a system of N particles and you know how they interact (which is a massive assmption) you can pretty much simulate its evolution, if you have enough computing power and/or enough time to let the computer do the math. That part is actually really important in studying how galaxies evolve for example, where you might for example simulate the evolution of a system consisting of a central massive black hole, a billion stars, and a few million solar masses worth of gas, to see exactly what happens to it, and then compare that for example with the properties of the galaxies in the Hubble Ultra Deep Field to see if they match at a certain time.
On anything more theoretical than that i'm really not sure since it isn't my field, sorry  for example, i don't really know how the uncertainty principle interacts with things like Hawking's radiation or black hole's entropy.
Other than just figuring out exactly what our Universe is like and how it works on a grand scale, which is no small feat, astrophysics like any other kind of basic research provides massive technological developments. People have this wierd way of looking at scientific research in a vacuum, but it's really unpredictable to say exactly what will come out of it, since well, we haven't discovered it yet. Yet, without Fourier analysis we woulnd't have jpeg files, without Hilbert spaces and quantum mechanics we wouldn't understand semiconductors, meaning we could kiss microprocessors goodbye, without general relativity we woulnd't have GPS and so on.
To be fair, as Feynman once said "physics is like sex, sure it has practical uses but that really isn't why we do it". I want to do research because it just makes me feel happy, i feel like it's what i was born to do. The first time i walked into a telescope's control room i felt like i was home.
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Normal, non-quantum gravity is so simple and intuitive though
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I haven't done integration in 5 years tho 
I also don't recognize upside-down delta or O with an I through it.
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Italy12246 Posts
Ah also, non-quantum gravity also inclues General Relativity. Believe me when i say that shit isn't simple and it's certainly not intuitive
Upside down delta V is the gradient operator in that case. O with an I through it is the greek letter phi and in this case it represents the gravitational potential. So yeah, math
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28090 Posts
Lots of interesting stuff here, I'm really enjoying reading what you have to say. I took some Astro/Physics electives and I was really tempted to go into it as well (which I didn't).
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28090 Posts
Also I featured your blogs. Blue staff member and makes great blogs, how were you not already featured
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Italy12246 Posts
Dunno i don't really make blogs that often
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Germany25657 Posts
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How have galaxy clusters and superclusters been confirmed?
Is it just a matter of putting all observable galaxies on a 3D grid and looking at the interactions?
Or is the concept of clusters based on unproven theoretical assumptions?
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Some more factual comments since I got hold of an actual keyboard:
- as a formerly theoretical physicist, I am still quite reserved with respect to inflation. It has so much "elegance reasoning" in it that if I took some of the common arguments for supersymmetry and exchanged a few words, you won't even notice that I am not giving you the standart reasoning for inflation. And you probably know how well it went with supersymmetry until know. But that's more of a personal point - anything that just supposedly happened once in a very distant past and is not possible to recreate is very difficult to "prove" at the level of rigor of experimental physics.
- the quantum theory of gravity is an interesting problem that puzzles people for decades. It is obvious and well-known that the most straightforward approach is pointless - you can't just take flat (or any for that matter) spacetime as the free theory and built a spin-2 graviton perturbation theory around it - for many reasons: because the free/interacting dichotomy doesn't make any sense in GR (first and foremost because it is not invariant to transformations), because there are no renormalisable interactions of spin-2 particles and also because of such fun technical details such as that the hamiltonian of GR is identically zero for physical solutions. So you have to think of something else. One widely beloved approach is the strings, but I was really amazed when I got some lectures on loop quantum gravity, because that's incomparably more straightforward (but also with many issues). A fantastic insight was when the professor has shown us that when we are forced to abandon any notion of "background metric", we are getting rid of all geometry and everything reduces to just combinatorics. The idea that the whole universe is based on counting combinations of triangles is simply wonderful.
- I would like to reinforce your idea that there is job market for you. If you like doing research, I can't imagine you not getting a good job, particularly if you are willing to move a little around Europe. I know from my US friends that the situation overseas may sometimes seem dire, but at least in the EU, astrophysics is now in a pretty big surge and there are positions of various levels - everything depending on your skill and financial demands. However a word of warning that you probably already know: the part when you actually do research may sometimes not be the majority of your time, because of paperwork needed to get funding - and that's annoying for many people and even drives them away.
Anyway, I have read some of your texts (not all sadly) in this blog and you are pretty good in expressing ideas, so you have a good disposition to teach and write, skills that will make job finding easier and the job potentially more rewarding (teaching is awesome, I can atest to that).
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United States24701 Posts
Thank you for writing up this summary and compiling a beautiful group of photographs.
Something you didn't talk about but I find fascinating is gamma ray bursts.
edit: As you can see, Hubble and I basically share a birthday!
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I thought quark stars are fairly likely. We haven't observed any black holes of less than about 5 Solar Masses, and the Chandresekhar Limit is something like 3 Solar Masses for a neutron star.
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On April 25 2015 01:39 Teoita wrote:
Sure, about what? There's is so much stuff to write about it really is impossible to include everything without writing a book, even without showing any math
Could you talk elaborate a bit on the "dust" and the dark nebulae, please?
Edit: also this blog was so good I read the whole thing, and almost all the comments, before going and looking at the new post in SFW Random pics that make you laugh.
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On April 25 2015 10:45 Just_a_Moth wrote:Show nested quote +On April 25 2015 01:39 Teoita wrote:
Sure, about what? There's is so much stuff to write about it really is impossible to include everything without writing a book, even without showing any math Could you talk elaborate a bit on the "dust" and the dark nebulae, please? Edit: also this blog was so good I read the whole thing, and almost all the comments, before going and looking at the new post in SFW Random pics that make you laugh.
I hope you don't mind if I take a crack at this.The dust is fairly complex when it comes to composition. You have grains of carbon (think graphite), silicates, and some organic compounds (including ethanol :D). These grains and molecules range in size from several microns to several tenths of a nanometer and contribute the majority of the opacity of these clouds, but they make up a fraction of the mass of the cloud. Hydrogen is ~70% of the mass of the interstellar medium, with Helium making up most of the rest.
Here's a link to the journal article that first discovered alcohol in the interstellar medium. It has a few good puns toward the beginning and end of the article.link
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I watch "Into the Universe" all.the.time.. It's fascinating, I would love if you posted more about this!
Curious, what do you make of the so-called "Supervoid"?
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On April 25 2015 11:50 Mordanis wrote:Show nested quote +On April 25 2015 10:45 Just_a_Moth wrote:On April 25 2015 01:39 Teoita wrote:
Sure, about what? There's is so much stuff to write about it really is impossible to include everything without writing a book, even without showing any math Could you talk elaborate a bit on the "dust" and the dark nebulae, please? Edit: also this blog was so good I read the whole thing, and almost all the comments, before going and looking at the new post in SFW Random pics that make you laugh. I hope you don't mind if I take a crack at this.The dust is fairly complex when it comes to composition. You have grains of carbon (think graphite), silicates, and some organic compounds (including ethanol :D). These grains and molecules range in size from several microns to several tenths of a nanometer and contribute the majority of the opacity of these clouds, but they make up a fraction of the mass of the cloud. Hydrogen is ~70% of the mass of the interstellar medium, with Helium making up most of the rest. Here's a link to the journal article that first discovered alcohol in the interstellar medium. It has a few good puns toward the beginning and end of the article. link
Thanks man.
Just wondering if you know more than the wrote, cause you said it's fairly complex, if so I'd be happy to hear about it if you're willing to type it out.
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I actually find this stuff really interesting and almost wish I could go back in time to study it at uni in lieu of what I took . I wanted to be an astrophysicist when I was little but didn't want to put in the time and effort (more or less). Finances and some other things were also part of the reasoning though.
Cool stuff and pretty pictures though. Also, I'd still like to take you up on a visit the next time that I come to Italy, whenever that may be .
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On April 25 2015 13:23 Just_a_Moth wrote:Show nested quote +On April 25 2015 11:50 Mordanis wrote:On April 25 2015 10:45 Just_a_Moth wrote:On April 25 2015 01:39 Teoita wrote:
Sure, about what? There's is so much stuff to write about it really is impossible to include everything without writing a book, even without showing any math Could you talk elaborate a bit on the "dust" and the dark nebulae, please? Edit: also this blog was so good I read the whole thing, and almost all the comments, before going and looking at the new post in SFW Random pics that make you laugh. I hope you don't mind if I take a crack at this.The dust is fairly complex when it comes to composition. You have grains of carbon (think graphite), silicates, and some organic compounds (including ethanol :D). These grains and molecules range in size from several microns to several tenths of a nanometer and contribute the majority of the opacity of these clouds, but they make up a fraction of the mass of the cloud. Hydrogen is ~70% of the mass of the interstellar medium, with Helium making up most of the rest. Here's a link to the journal article that first discovered alcohol in the interstellar medium. It has a few good puns toward the beginning and end of the article. link Thanks man. Just wondering if you know more than the wrote, cause you said it's fairly complex, if so I'd be happy to hear about it if you're willing to type it out.
lol "fairly complex" is a physics excuse. I really don't know much more than what I wrote. I just checked one of my books and found out this though. There isn't much we can do to detect these clouds. There are a few things we can tell though. Photons tend to interact with things that are roughly the same as their wavelength. When we look at these clouds, they absorb background light in wide swaths of the spectrum, so we can tell that they range in size greatly, from a few tenths of a nanometer to a few microns. We can tell because all the way from hard UV to far infrared is blocked out.
A few other clues we have come from some other absorption lines. We see fairly specific lines that correspond to the amount of energy needed to interact with bonds between silicon and oxygen and bonds between Carbon atoms in polycylic aromatic hydrocarbons (PAHs). One thing I read in my book is that the PAHs are sort of daisy chained together to form really big molecules similar to graphite. Another interesting thing I found is that, if there is water around these dust grains, they can get a kind of icy mantle around their rocky core. Probably not applicable to dark nebulae, it's cool to think of these little dust grains as tiny little Enceladuses. These observations are what suggest that the dust is like extremely fine sand (the silicates) and extremely fine graphite (the PAHs). On Earth we would call the dust a colloid or silt, and there may even be some very fine sand. To give you an idea of the size of particle, some of the particles are smaller than the globs of fat in homogenized milk. Basically, this stuff is not like much anything we have on Earth.
Finally, let's talk about density. Dark Nebulae typically have a number density (this is the number of particles in a given volume rather than mass per volume) of about 100 - 300 particles per cubic centimeter. Using a classic physics trick, we can say that roughly one of those will be a dust particle. The average separation between these tiny dust grains is much greater than the separation between dust particles on a fairly clear day on Earth. The reason these clouds block out so much light is because they are big. They are generally on the order of about 100 light years across. Just as a point of comparison, the Sun is in a fairly lowly populated region of the galaxy and is ~4 light years from its nearest neighbor. Within 50 light years on either side of the Sun are hundreds of stars.
Honestly though, the best I can do from here is give you links: Wikipedia entry for Cosmic Dust
Wikipedia entry for ISM
Wikipedia PAH
Wikipedia on Grain Size -- Sort of tangential but kind of interesting if you reaally want to know about the kind of sizes of particles
Enceladus: The best or worst place to play hockey
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I can't even express how happy it makes me that this blog/thread exists on Team Liquid. THIS is why I love all you people.
Teo, it'll be a few years yet before I'm employed as an astrophysicist, but maybe I'll see you around at a conference or something someday. I'll make sure I always wear my TL pin on my suits 
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EPT![[image loading]](http://ej.iop.org/images/0004-637X/487/2/617/Full/df1.gif)
