That isn't a bad assumption to make. Take a star with spherical shell density proportion to 1/r^3. Perform a scale factor transformation to r* such that the spherical shell density per unit length is uniform for the new scale factor. Solve for the quasistatic collapse of a uniform density star. Perform an inverse scale factor transformation on the collapsed uniform solution. Nothing wrong with transformations to make the math easy. Solving for a simplified case sometimes makes solving a less trivial case easier, so long as there is a simple relationship between simple and complex cases.

Also, a simplified case places constraints on the solution for a more complicated case. The density of a spherical cow is the lower bound for the density of a non-spherical cow.

Speak for yourself, bud. I want real news but I want news of interest to me. I don't care about sports, politics or what the latest celeb said or did. I want science and technology, and I have and would pay for that kind of news. Websites and RSS feeds allow people to pick what interests them. Print doesn't. Bring on personalised newspapers.

Bravo, Mr Bolden! NASA does exceptional work. Sometimes the armchair critics should just STFU and let NASA get on with the fun stuff.

Which is why drug trials use double blind procedures. A placebo effect is unlikely to correlate when neither the researchers nor the patients know beforehand which is the test medication and which is the control medication.

Let me think...An army truck is secretly transporting a nuclear device through downtown New York. A random pothole bounces the truck and jars the device, accidentally changing it to armed status, while also tearing the break cables. The truck loses control and crashes into the Wall Street Stock Exchange. The armed and unstable nuclear device detonates wiping out the financial district, crippling the US economy in the nuclear disaster. The skipper of an oil supertanker is blinded by the detonation flash and crashes into Manhattan island, tearing the hull and spilling 2million barrels of oil into New York harbor.

No single software bug can do all those things either. Most bugs only end up with someone swearing at the computer while they reboot. Quite often it's the human in the control loop doing something unexpected that leads to failure of mission critical systems.

I bought a Dell XPS710 in 2007, dual core processor running at 2.66GHz, Win XP Pro, 4GB Memory, 768MB NVIDIA GeForce 8800GTX. It ran Win 7 Ultimate quite happily for years and allowed me to play games like Skyrim, Diablo 3 and even Crysis. Memory was the main resource issue. The processor and card doesn't need to be that powerful, so long as you are realistic about the background processes and Aero settings.

Gravity waves have already been proven to exist. The 1993 Nobel Prize in physics was awarded for the study of the Hulse-Taylor binary pulsar that showed indirect confirmation of the existence of gravity waves http://en.wikipedia.org/wiki/H....

Gravity wave detection is expected within the next 20 years from the LIGO programme http://en.wikipedia.org/wiki/G..., http://www.ligo.caltech.edu/ and http://en.wikipedia.org/wiki/L.... It won't require a thousand years, nor is it beyond existing technology. LIGO is already taking measurements in the US, at Hanford and Livingston, and advanced LIGO will increase the sensitivity of the LIGO interferometers by a an order of magnitude, and is expected to increase detection rates from a few per year to 100s per year by increasing the detection volume a thousand fold. If advanced LIGO doesn't detect anything, then it will be time to review the theory.

(I worked for ~6 years at the University of Western Australia in the physics department in collaboration with the Australian LIGO research group)

Easy statement to refute. I am an atheist and a research physicist and I can definitely confirm that I DON'T GET ENOUGH SEX!

Or money.

I'm kind of upset about that. ;-(

Not convinced your example proves Neil wrong. Commercial satellites are common only because the US and Russian governments did all the primary research and development first. Satellites aren't as fragile as humans and considerably easier to launch into space and keep there. Near Earth orbit is easier and cheaper than Mars.

Neil is commenting mainly on "Elon Musk's boast that he would establish a Mars colony". Manned travel to Mars isn't routinely done and there isn't anything for \industry to build on. The cost to develop and test the technology to make manned trips to Mars feasible and to sustain a base on Mars would be prohibitive for a single commercial industry. Look at the development of the electric car for instance. Significant cost and research required as well as infrastructure changes and no single commercial entity was responsible for the full development of the technology required to make hybrids and full electric vehicles commercially viable.

As for the cost, getting a manned Mars trip down to $100/kg is a significant undertaking. I'm sure that if the costs could be bought down to that level that commercial interest would peak. But that is a far cry from doing it now before the technology has been developed, as Elon Musk seems to boast.

-Wayne

PS Secretly I'm hoping Elan can do it, but the chances are slim to none.

Not really. The scientific definition of a resonant system is a system where the amplitude increases in response to an external driving force. This happens over a narrow frequency band or resonance band and corresponds to the natural frequency or frequencies of oscillation of the resonant system. Time crystals don't require an external driver to show a periodic response. JustinOpinion (http://science.slashdot.org/comments.pl?sid=3704889&cid=43599995) explains the Time Crystal concept quite well.

Well, a crystal is a repeating arrangement in space where each atom occurs in certain regular positions in the crystal structure. If you look along any direction in the crystal the crystal lattice is repeating and predictable. A time crystal is the same idea but it is repeating in the direction of time. For instance any shape that changes but repeats that same pattern over time in a regular and ordered way would be a time crystal. I'm sure this is a simplification. For instance, I suspect a simple mechanical device (such as a clock) wouldn't constitute a time crystal any more than a tank full of loose balls would constitute a spacial crystal. In fact, I suspect the time crystal would need to be self organising in the same way that a spacial crystal self organises. In other words, the time crystal cycle is self perpetuating, hence the link to perpetual motion and the rather uncomfortable feeling that something might not be correct in the theory. In a spacial crystal it is the charges in the atoms and ionic bonds that self organise the crystal. For a time crystal (and I'm speculating here since I haven't read the arXiv article), maybe the transfer of energy or spin around the crystal would self organise the time crystal.

'Hone' means to focus in or to work towards a specific goal, and is listed in reputable print dictionaries (i.e. http://www.merriam-webster.com/dictionary/hone%20in). Honed in is the past tense of hone in. It is true that some people think it is wrong, and that opinion is open to debate, as it should be for any living language. But the deciding factor is whether the intent of the phase is understood by the majority of readers. Since it is in common use, it follows that it has become accepted phraseology.

Methinks Google translate is having trouble with Finnish to English. From TFA

You could say that about anyone. As a scientist I expect as much privacy as anyone else.

That doesn't mean he was right. The prevailing opinion at the time was for a static, unchanging universe. And the discovery that it was expanding would have been difficult to reconcile with our understanding at the time. Prevailing opinions do change, albeit sometimes slowly, in the face of mounting evidence.