For once, I'm siding with the over-aged hippy. This is known as Olbers' paradox. Only an infinitely old, static universe would have uniform light intensity throughout the universe. A finite, expanding universe does not. Also, keep in mind that when a cosmologist says the universe is homogeneous they are speaking on ridiculously extremely large scales. Obviously, if you can look outside and see the Milky Way then you see that there are more stars in one spot and fewer elsewhere. So talk about homogeneous you have to go much beyond our galaxy, and our "local" cluster of galaxies to a very large distance.
Aside from the fact that making scientific laws is a bit of an antiquated idea Is that a fact? We abuse the terminology of what distinguishes a law from a theory that everyone learns in middle school science classes. Even laws, such as Newton's Laws have domains of applicability. The Theory of General Relativity had been proven to describe nature extremely well and is theoretically extremely well motivated, and it should be differentiated from other theories such as String Theory, which may just be wild speculation.
First off, let me say I'm not a fan of dark energy, and I've been rooting against it for a while now, so I can't really defend it for you. We're in deeply subjective territory now, but I can offer a few reasons why scientists have been taking it seriously:
1) Timescales - A decade is not a particularly long time in the development of a scientific theory. We couldn't even ask these questions 10 years ago, and it is only since the WMAP results were published in late 2003 that we can do precision cosmology, and start seriously poking at the models. It took a decade for Einstein to go from special to general relativity. It took over two for the standard model of particle physics to come together to explain the new particles being produced at accelerators. It shouldn't be a great a surprise that the models we had in place would be pushed until they broke and then updated, and these things just move slowly.
2) Dark Matter - It is very important to realize that the standard model (of cosmology) predictions for dark matter have been more or less confirmed through recent studies of gravitational lensing (we measure light being bent by matter, then use telescopes to count up the matter, and the discrepancy is "dark" matter). Theoretically, dark matter and dark energy are on different footings since we have several possible known dark matter candidates in particle physics, while the best guess candidate for dark energy was vacuum energy which turned out to be the worst prediction in physics (off by about a factor of 10^60). Nonetheless, the success of dark matter gave credence to dark energy.
3) Difficulty - I may have earlier made Wiltshire's contribution sound over-trivialized. Even for Ph.D. physicists, the sort of model Wiltshire uses leads to really, really hard math. People have been continually developing general relativity-based models with both analytical solution approaches and cosmological averaging, like Wiltshire uses. Implementing the idea is difficult, but this leads to a larger issue. I could say that instead of wasting their time on endless (fill in the blank), computer scientists should just work on finally making a perfect operating system. But that is silly, at some point the operating system is good enough, and some people start writing applications. Same thing with physics: when you have a good, workable theory in place some people start working on the applications and consequences. Some people only work on operating systems or fundamental theories in physics, but everyone else just uses them for what they are, and those people tend to get most of the fame and fortune. It is just a reality of life.
Here's the slightly more condensed version of this story. Einstein's theory of General Relativity (GR), which incidentally should the Law of GR by today's standards, gives a large set of differential equations to be solved. When this was first being applied to Cosmology in the 1920's, some basic assumptions about the universe had to made in order to solve the GR equations: it is isotropic (same in all directions), and homogeneous (uniform everywhere). They were primarily made for two reasons: mathematical expediency (this is the simplest sort of non-trivial universe you can have), and this didn't conflict with any observations at the time. Solving the GR equations with these assumptions gives fairly simple equations for the time evolution of the universe, leading to the standard model of Cosmology (called the Lambda-CDM model).
As you would imagine, we have vastly more astronomical data now then we did in the 20's. To explain what we observe now, particularly the cosmic microwave background data, with these evolution equations we need to include a constant expansion term. This expansion would have to be from something uniformly distributed throughout the universe with negative pressure (very reminiscent of phlogiston, isn't it?) which we call "Dark Energy". So, based on current data and using the standard model to explain certain properties of the universe, it must consist of around 73% dark energy. Considering that this is the bulk of the universe and that, other than negative pressure, we have no idea what dark energy is or what it's properties are, this leads to a scientifically troubling state of affairs.
However, modern sky surveys show that the universe is neither isotropic nor homogeneous. Instead there is a tendency towards a bubble-like structure with large empty spaces surrounded by thin "filaments" of galaxies. Even still, the standard model which requires dark energy ignores these differences. So, Wiltshire's contribution is to replace the standard assumptions with this "bubble" model, re-solve the GR equations, and get new equations for the evolution of universe based on it's *observed structure*, not some simplified model. In his new equations, dark energy is completely unnecessary. Since the structure of these "bubbles" is so large, fits to the data with Wiltshire's model are statistically just as good (actually indistinguishable) as the standard model, though as a caveat not all of the calculations have been done. Not only is Wiltshire's model much better from an Occam's Razor standpoint, it may actually solve some mysteries which the standard model cannot explain.
I really can't go any further and still call this a "condensed" version with a straight face. In/. articles in other fields, I enjoy reading the commentary from experts, so here's an attempt to reciprocate. Hope this helped.
Slashdot Mirror
For once, I'm siding with the over-aged hippy. This is known as Olbers' paradox. Only an infinitely old, static universe would have uniform light intensity throughout the universe. A finite, expanding universe does not. Also, keep in mind that when a cosmologist says the universe is homogeneous they are speaking on ridiculously extremely large scales. Obviously, if you can look outside and see the Milky Way then you see that there are more stars in one spot and fewer elsewhere. So talk about homogeneous you have to go much beyond our galaxy, and our "local" cluster of galaxies to a very large distance.
First off, let me say I'm not a fan of dark energy, and I've been rooting against it for a while now, so I can't really defend it for you. We're in deeply subjective territory now, but I can offer a few reasons why scientists have been taking it seriously:
1) Timescales - A decade is not a particularly long time in the development of a scientific theory. We couldn't even ask these questions 10 years ago, and it is only since the WMAP results were published in late 2003 that we can do precision cosmology, and start seriously poking at the models. It took a decade for Einstein to go from special to general relativity. It took over two for the standard model of particle physics to come together to explain the new particles being produced at accelerators. It shouldn't be a great a surprise that the models we had in place would be pushed until they broke and then updated, and these things just move slowly.
2) Dark Matter - It is very important to realize that the standard model (of cosmology) predictions for dark matter have been more or less confirmed through recent studies of gravitational lensing (we measure light being bent by matter, then use telescopes to count up the matter, and the discrepancy is "dark" matter). Theoretically, dark matter and dark energy are on different footings since we have several possible known dark matter candidates in particle physics, while the best guess candidate for dark energy was vacuum energy which turned out to be the worst prediction in physics (off by about a factor of 10^60). Nonetheless, the success of dark matter gave credence to dark energy.
3) Difficulty - I may have earlier made Wiltshire's contribution sound over-trivialized. Even for Ph.D. physicists, the sort of model Wiltshire uses leads to really, really hard math. People have been continually developing general relativity-based models with both analytical solution approaches and cosmological averaging, like Wiltshire uses. Implementing the idea is difficult, but this leads to a larger issue. I could say that instead of wasting their time on endless (fill in the blank), computer scientists should just work on finally making a perfect operating system. But that is silly, at some point the operating system is good enough, and some people start writing applications. Same thing with physics: when you have a good, workable theory in place some people start working on the applications and consequences. Some people only work on operating systems or fundamental theories in physics, but everyone else just uses them for what they are, and those people tend to get most of the fame and fortune. It is just a reality of life.
And now you know the rest of the story...
I am, for the record, a physicist.
/. articles in other fields, I enjoy reading the commentary from experts, so here's an attempt to reciprocate. Hope this helped.
Here's the slightly more condensed version of this story. Einstein's theory of General Relativity (GR), which incidentally should the Law of GR by today's standards, gives a large set of differential equations to be solved. When this was first being applied to Cosmology in the 1920's, some basic assumptions about the universe had to made in order to solve the GR equations: it is isotropic (same in all directions), and homogeneous (uniform everywhere). They were primarily made for two reasons: mathematical expediency (this is the simplest sort of non-trivial universe you can have), and this didn't conflict with any observations at the time. Solving the GR equations with these assumptions gives fairly simple equations for the time evolution of the universe, leading to the standard model of Cosmology (called the Lambda-CDM model).
As you would imagine, we have vastly more astronomical data now then we did in the 20's. To explain what we observe now, particularly the cosmic microwave background data, with these evolution equations we need to include a constant expansion term. This expansion would have to be from something uniformly distributed throughout the universe with negative pressure (very reminiscent of phlogiston, isn't it?) which we call "Dark Energy". So, based on current data and using the standard model to explain certain properties of the universe, it must consist of around 73% dark energy. Considering that this is the bulk of the universe and that, other than negative pressure, we have no idea what dark energy is or what it's properties are, this leads to a scientifically troubling state of affairs.
However, modern sky surveys show that the universe is neither isotropic nor homogeneous. Instead there is a tendency towards a bubble-like structure with large empty spaces surrounded by thin "filaments" of galaxies. Even still, the standard model which requires dark energy ignores these differences. So, Wiltshire's contribution is to replace the standard assumptions with this "bubble" model, re-solve the GR equations, and get new equations for the evolution of universe based on it's *observed structure*, not some simplified model. In his new equations, dark energy is completely unnecessary. Since the structure of these "bubbles" is so large, fits to the data with Wiltshire's model are statistically just as good (actually indistinguishable) as the standard model, though as a caveat not all of the calculations have been done. Not only is Wiltshire's model much better from an Occam's Razor standpoint, it may actually solve some mysteries which the standard model cannot explain.
I really can't go any further and still call this a "condensed" version with a straight face. In