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Comment Re:Are we looking through the center... (Score 1) 157

We don't know that the speed of light was always as it is now.

The speed of light is inversely proportional to two universal constants, the permittivity and permeability of free space. Both of these constants have observable effects, particularly permittivity which governs the strength of electrostatic interaction and therefore effects the absorption/emission spectra of atoms. We don't need to assume that the speed of light is constant at other regions in space. We can confirm it.

Comment Re:Seems... facile (Score 1) 231

How can we definitively tell if the vacuum over there has the same energy density as the vacuum over here?

This comes from measurement of the fine structure constant. The virtual particles created as a result of the vacuum energy interact with electrons, causing small changes in the elementary change of the electron, and int he electromagnetic coupling between charged particles. This effect is accounted for in QED, and has been observed in the spectra of Hydrogen as difference in the energy levels of 2S1/2 and 2P1/2 orbitals ( Measurement of the fine structure constant from atomic spectra allows us to measure if the elementary electric charge has changed over time or at different locations in the universe, essentially a remote measurement of the uniformity of vacuum energy.

Some measurements do suggest that the fine structure constant has changed over time, or that it isn't uniform throughout space over galactic scales. Indeed, there is no reason why it should be. That said, I would be surprised if the inhomogeneity is balanced by the accelerating expansion rate of the universe. Hence the problem of apparent increase in energy and violation of conservation of energy.

Comment Re:Hmmm ... (Score 1) 356

Looks like a hell of assumption to make about stellar density. We know the cores are way more dense than the rest of the star, that's the magic that makes the fusion happen.

Now if this assumption is qualified and addressed later in the paper, I'll be guilty of not being careful enough, but I haven't found that clue yet.

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.

Comment Re:They do mind. (Score 5, Interesting) 113

People do not want real news. They want infotainment.

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.

Comment Re:Where do you draw the line? (Score 2) 650

I don't know of a car flaw that can tank an economy, cause a nuclear disaster or cause oil to spill out into the sea. But a software flaw can do all these things.

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.

Comment Re:the one flaw in that (Score 1) 860

There's one flaw in that complaint. The last computer sold with XP that would be unbelievably fast would likely be an early core duo or core 2 duo or Phenom x6 AM2 socket with 8GB of RAM and a sub-100MB/s SATA drive and a gTX285. That system overall is pathetic and wouldn't run Windows 7 very well at all not to mention its insanely inefficient energy usage. Back in reality, most have 1-2GB of RAM, a pathetic hard drive, and an even more pathetic chip, usually a single core. So to say "replace your device" as the most recommended step um yeah. The youngest XP device from a normal manufacturer would be 7 years old right now. Time to go.

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.

Comment Re:is there an xkcd comic for this? (Score 5, Informative) 138

Just because it's ridiculously hard to prove doesn't mean that it's false. For example, most physists believe gravity needs a force carrier which they've called a "graviton", the same way light (electromagnetic radiation) consists of photons. That theory is 80 years old and still totally unproven but as long as nobody has a good competing theory we still kind of assume that's how it works.

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

Not that we're not trying to look for gravitational waves and other clues, but most of it is so far off the scale of what we can experimentally detect that it'll probably still be unproven in a thousand years.

Gravity wave detection is expected within the next 20 years from the LIGO programme, and 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)

Comment Re:Perverse incentives (Score 1) 1293

Allow me to rephrase that: "Long story short, if someone is vilifying religion and praising science, they are doing it solely for the sake of their own pocket book(and perhaps marital bed)"

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. ;-(

Comment Re:I suspect he's right. (Score 2) 580

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.


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

Comment Re:What does this have to do with time? (Score 1) 231

Isn't that colloquially called resonance?

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 ( explains the Time Crystal concept quite well.

Comment Re:What does this have to do with time? (Score 2) 231

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.

Comment Re:language issues? (Score 4, Informative) 164

'Hone' means to focus in or to work towards a specific goal, and is listed in reputable print dictionaries (i.e. 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.

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