Locrian

No, that isn't the same at all. The first statement you made is a broad, qualitative statement that predicts little and doesn't make sense in the face of modern scientific knowledge. Einstein's paper in 1905, on the other hand, was a specific derivation that quantitatively predicts the value of energy produced and was entirely based on well known scientific principles of the time. There's no reason the second should follow from the first.

There is a connection: You can't do anything useful with either of them.

This is typically how it is done. However, some SEM's - including the one I typically work with - can operate at higher pressures, allowing the small amount of gas in the chamber to remove this charge. We regularly take pictures of non-conductive plastics, and even have some interesting picutres of organic matter. Sort of off topic, but I thought you might want to know in case you ever needed it!

Gib65, keep in mind that only condensations that have integer spin can be bose-einstein condensates, which doesn't include an awful lot of matter. Also, the very idea of everything condensing in a heat death scenario is pretty much the opposite of what is expected to happen.

US information. Thanks for having me clarify.

One other thing though I would like to add to this discovery of the cosmological constant: Schmidt's first appeared in the astrophysical journal. The second, which blew the lid off the acceleration business, did not. It appeared in a much less well known journal. At a later date, a third appeared again in the astrophysical journal. I've always thought it fun to question why those were published where they were. I could be wrong, but I'd think there is some drama in that story somewhere.

I'm glad you liked it. I've done a better job in the past, and if the question comes up in the future I'll do a better job then. And you are right about Permutter. I also see a Schmidt. Here are the papers I have jotted down, though there are several others that are important: Riess et al. “SNAPSHOT DISTANCES TO TYPE Ia SUPERNOVAE: ALL IN “ONE NIGHTS WORK.” Astrophysical Journal, 504 935-944 (1998) Schmidt et al. “THE HIGH-Z SUPERNOVA SEARCH: MEASURING COSMIC DECELERATION AND GLOBAL CURVATURE OF THE UNIVERSE USING TYPE Ia SUPERNOVAE.” Astrophysical Journal, 507 46-63 (1998) Unfortunately though I am embarassed to say you have misjudged me. I am neither quickwitted nor well informed. This leaves me in a tough position to respond to the rest of your post, and the suggestion that my response should be interesting definitely (and maybe thankfully) precludes me from putting my neck on the block. I hope someone else gives it a shot, as you deserve a response.

You mention aerospace; be careful with that area. That field has regular boom-bust cycles, and engineers out of the USSR and China are often willing to work for far less than you would probably want to get paid. When considering salaries you'll hear for the field, always remember that those averages rarely take into account those people who are unemployed (and therefore making nothing at all), which would tip the scale considerably. As for astrophysics, if you are an excellent student and go to a good (but not incredible) university you can expect to pay for your college, be supported (with a small stipend) during your graduate work, and spend anywhere from 4-8 years as a postdoc making 30k. Once on a tenure track - assuming you get one - you'll be making 40-60k for a while, before you start making closer to 80-90k much later on. Obviously these numbers are different per college, but I believe they are fair averages. Note that you get that "professor" pay up to 25 years after you start college, and consider that into the opportunity cost for the profession. So the pay stinks, but if you love the area it could be very well worth it. Also, if you love the area I doubt it will get repetitive and boring, unless of course you just aren't very good at it. To answer your question about wide and narrow, astrophysics is pretty narrow. There are very few jobs you'll be able to get outside the university field, and be critical of anyone who says otherwise. So you've really asked one question about two very different things, aerospace engineering and astrophysics. If you decide you love astronomy, then more power to you. However, I will give you this warning: there are many, many fascinating things in this universe. It is possible to get a high school and college degree without running into most of them. Consider the possibility that there are other things you enjoy just as much that have better job prospects, and keep an open mind.

This is undoubtedly true! Of course I don't think it helps much, because now we can just ask the question - which definition makes the most sense? If you asked someone for water you wouldn't accept steam. Despite the fact that they have the same constituents, they have different properties and the fact that they are interchangable doesn't relieve us from having different names for each. Physicists who deal with subatomic particles on a regular basis may find the term "fermion" and "matter" pretty close to interchangable, but for most people, including many physicists, subatomic particles simply lack the characteristics we generally associate with matter. It is still my opinion that if we want to be clear with what we mean, matter refers to something more than the parts it is made of.

I can think of lots of cases where it's irrelevant. If you ignore time and consider a static system the second law is irrelevant. Given near infinite time the universe could become so devoid of potential that nothing will happen and the second law could become irrelevant. What it can't be is wrong. To see why you actually have to consider philosophy as opposed to physics, and ask yourself what that law says.

In the late 90's some astrophysicists (Reiss, anotherbignamei'veforgottenbutwilllookuplater, et al) did some work to determine how fast the universe was expanding. They were using supernovae to do distance/redshift measurements, and hoped to measure how much the expansion of the universe was decelerating. The first big paper was actually included the word "deceleration" in its title. For the past 60-70 years a deceleration was assumed because there was no known force to cause an accerleration, and there was a known force to cause a deceleration - gravity. There was a problem with their paper though. If you read to the very end, they come up with a negative value for this deceleration. Over the course of the next couple of papers they published it became clear that the universe is accelerating its expansion. Many groups have repeated this study. There is little or no argument that it is valid. Since there is an acceleration, there must be a force. This is typically called the "cosmological constant," thanks to our most famed and overrated scientist, Einstein. You may also see it called "quintessence." That this force exists there is little doubt. Of its exact value and whether this value is constant over time and space, there is much more doubt. The fact that there is this potential energy threw a huge monkey wrench in quite a few theories, especially string theory*, but actually did a great deal to validate the inflationary big bang theory. *I remember reading a paper at the time saying something like "you can get anything you want out of string theory except a small, positive cosmological constant"... but of course, that was five years ago, so its ancient history. Now people working in string theory will tell you that a small, positive cosmological constant is a natural outcropping from their... well, whatever you want to call what they've got.

I'd have to agree with you Gib65, while at the same time using his definition of matter. To me, two particles that have mass but are best described by wavefunctions don't "occupy space" in the traditional sense. They don't have positions, they have probability distributions that describes the chance of them being measured somewhere. I see matter as emerging from the condensation of multiple particles. It may still only be made up of fermions, but, in short, the whole is more (or at least different) than the sum of its parts.

Thanks for the link to Hsu's blog, Martin! I have added it to my ever growing list.

He's saying the particle is in both states until it's measured. Remember, an object has spin, but it isn't "spinning" in any usual sense of the word, so it doesn't make sense to say that it's "spinning permanently."

That's an interesting thought experiment. However, shouldn't we see a large number of objects that look basically identical in your proposed universe?

No, there is only one time involved. You can see this by just looking at the equations involved and observing that there is only one variable for time. In this case, taking observations "over time" is the same as taking observations over distance. I'm appalled you didn't make this connection.

This is not true either. If you look at Reiss and Schmidt's data, it is not from stars at that distance. It is from closer, and actually shows the universe is accelerating. You are making a very serious error here. I swear, between Mart's failure to understand the basic operation of science involved and everyone else's failure to get the facts right I'm begining to think people here haven't actually read the literature on the subject.

No one in science thinks it is dark matter that is causing this acceleration. You are confusing dark matter and dark energy. They are not the same thing.

Nobody assumes this. I can produce a nearly infinite number of mathematical systems that do not reflect reality, and everyone working in physics understands well that these exist.

Well I know cubic boron nitride and none of the carbides are harder than diamond at room temperature (most aren't even close on a linear scale), and I'm pretty sure none are harder below room temperature - however I admit I mostly deal with all of these materials at STP. If you could provide additional information I'd appreciate it. I know recently there was an announcement that someone had produced carbon nanotubes that were harder than diamond, but I really dislike their characterization. Frankly hardness just isn't the same at a nano level as it is at a macro level. It is also worth noting that some people have been growing CVD single crystal diamond that is harder than any measured natural diamond, so assuming that natural diamond is as hard as it gets wouldn't be fair.

Which ones are you thinking of?

Why would you think the assumption is that the system is unchanging with time? You said earlier that the rate of expansion was constant. You suggested before that that someone thought redshift was constant. Why do you keep bringing up arguments that no one is making? I realize you aren't arguing for these, but I don't even see how they belong in the conversation, since absolutely no one has taken up those arguments. If you don't understand how the observation of a system over time can lead to predictions for the system, then you are missing very basic fundamentals of physics. Maybe even fundamentals of science. Observation, theory and prediction are all basic scientific concepts that have been employed succesfully for several hundred years now.

lol those human beings and their history! Just another reason to enslave them. Seriously, there are like two or three equations copied from special relativity and then nothing. I have no idea what you even think is worth discussing about this.

Actually since most of the really big masses are near the center of the galaxy, newtonian approximations are not as invalid as you'd think. This paper presented has already had some very serious arguments made against it. In it they produce the correct rotational velocity by assuming there is a distrubution of matter within galaxies that has never been observed. Many are saying that this distribution is an unacceptable additional variable that basically amounts to assuming there is a new, difficult to observe matter inside galaxies. In otherwords, one argument is that these researchers are assuming there's dark matter in their proof there is no dark matter.

Firstly, no one suggests that N is constant. That's what this entire thread is about. You've said this a couple of times now and it doesn't make any sense. No we aren't. By taking data at various distances we are taking data at various times. By taking data at ever smaller distances we can accumulate data and then see if a function can represent that data. Of course there are ones that do, and we can use them to determine what is occuring at this time. No one assumes that what is occuring far away is still occuring; on the contrary, the whole point of the entire issue at hand (the discovery in the late 90's that the universe is accelerating) is to use how things were to predict how things are. This is something that can only be done because we are well aware that things aren't now as we see them. It is possible that the real issue you have here is one with science itself. That would make for an interesting philosophical discussion, but should be had in the appropriate forum. As for the science itself, when determining the rate at which space is expanding there is really nothing outside of standard physics principles used here.