Follow Slashdot stories on Twitter

 



Forgot your password?
typodupeerror

Comment: Re:This again? (Score 1) 472

by joe_frisch (#49601313) Attached to: New Test Supports NASA's Controversial EM Drive

There are still a lot of ways for the experiment to get the wrong result in vacuum. The force is really quite tiny.

Their "hard" vacuum was 1e-6 torr scale. That might still be enough to to produce some force. There can be effects from temperature causing anomolus forces in the suspension mechanism. There can be magnetic field effects from power cables. Torque from RF cables getting warm.

This would be a very difficult experiment to do correctly. Without details, it is much more likely that they got it wrong, than that they have found a violation of conservation of momentum.

As an aside, quantum mechanics still conserves energy and momentum. The pushing on virtual particles from the vacuum doesn't work unless you add enough energy to turn them into real particles - and then you just have a photon drive variant (which would produce far less thrust).

Comment: Re:Enough of this (Score 2) 248

by joe_frisch (#49601261) Attached to: Long Uptime Makes Boeing 787 Lose Electrical Power

Even though this bug isn't a direct threat, it could interact with other future software changes. If it is a counter overflow there is a risk that the counter would run at a higher rate in some future version where more functionality is needed. If 248 days went to 2.48 days, it might not be caught in testing, but could (rarely) happen in real life.

Comment: Re:Science requires a certain agnosticism (Score 2) 472

by joe_frisch (#49598641) Attached to: New Test Supports NASA's Controversial EM Drive

There is an old saying that you should keep your mind open, but not so open that your brains leak out.

When someone claims a violation of very well tested physical laws, AND that violation is not under some new unusual condition, it is very reasonable to be skeptical.

It this was seen with TeV protons at LHC, or in ultra-strong electric fields, or in strong gravity, or other unusual conditions it would be different. Physicists paid attention to the (later dis-proven) FTL neutrinos from CERN because that experiment was a new measurement under different conditions (very high energy neutrinos). We all expected (correctly as it turned out) that the effect was an instrumentation error, but we paid a lot of attention because it was possibly it was something extraordinary. This isn't.

Comment: Re:This again? (Score 1) 472

by joe_frisch (#49598617) Attached to: New Test Supports NASA's Controversial EM Drive

I have spent my life (or at least 35 years) studying physics and doing experiments, many of which include high power microwaves.

There are a lot of ways for them to have gotten this wrong, and it violates very fundamental physics principals. They can publish in a refereed journal with enough details to satisfy other physicists if they really have something.

Comment: Re:This again? (Score 1) 472

by joe_frisch (#49598601) Attached to: New Test Supports NASA's Controversial EM Drive

If you use energy to create real particles out of virtual ones, you are building something very like a photon drive. Its just like an LED converting electricity to matter (photons). Those photons produce thrust - but the thrust / power is extremely tiny. This limit applies to any sort of particles you might produce.

Comment: Re:This again? (Score 1) 472

by joe_frisch (#49598597) Attached to: New Test Supports NASA's Controversial EM Drive

There are a number of concepts for accelerator driven nuclear reactors. Nothing fundamentally crazy, just none have been made practical yet. I don't know if there is enough room to increase the efficiency of generating and collecting neutrons - it may be that you just can't quite get there. Similar situation to muon catalyzed fusion. It *almost* works, but the muons stick to the helium after it is formed and you can't quite come up with a scheme where it is a net energy producer.

Theses sorts of concepts are being looked at - they may eventually get one to be practical, but so far no.

Comment: Difficult experiment, clearly wrong . (Score 4, Informative) 472

by joe_frisch (#49598565) Attached to: New Test Supports NASA's Controversial EM Drive

Its not easy to measure 50 micro-newtons of force when you change a power level by 50 watts.

Currents cause magnetic forces. Things get hot and outgas producing thrust. RF power cables get hot and distort causing a force.

Think about it. The device weighs something like 5Kilos. That is 50 newtons gravitational force. So a 1 micro-radian tilt will cause a 50 micro-newton force. Walking across the lab floor could cause that amount of deflection. If the chamber is 1 meter across, a 0.1 degree temperature change on one side of the chamber (from a nearby power supply) could cause that much tilt.

There of course could be force just from photons - but that is a simple and well understood photon drive - known for at least 50 years now - basically a light-sail.

This is a very difficult experiment to do correctly, and they have not published in enough detail.

Meanwhile: conservation of momentum has been tested under conditions ranging from ultra-cold gas atoms to 100GeV particle collisions, to orbiting neutron stars. The RF fields they use are very modest. At SLAC we run hundreds of megawatts, not 50 watts. We have superconducting cavities where we easily see the deflection caused by the momentum in the microwave fields - operating at many thousands of times higher power than this experiment - we see nothing unexpected.

So: Difficult experiment. No unusual physical conditions. Apparent violation of one of the most carefully tested conservation laws in all of science.

It it literally more likely that the sun will not rise tomorrow (since that is also based on conservation of momentum) than that this experiment was correct.

Comment: Re:The best encryption: No encryption (Score 1) 225

It is quite possible to demand keys that someone *thinks* might be there. More is the pity if there never was any encrypted data on the device to begin with.

A lot of misbehavior from law enforcement seems to stem from them being "sure" of what is going on, despite a lack of evidence to support the surety.

Comment: Re:Help me out here a little... (Score 1) 533

by joe_frisch (#49513999) Attached to: Utilities Battle Homeowners Over Solar Power

Sure. But if a higher percentage of customers are using solar, then the utility is selling less power so there is less money available to support the infrastructure. They can either increase prices on the non-solar customers, or decrease the amount of money they pay when solar is put back on the grid.

If you do the former, at some point the price gets high enough that everyone is forced into local power generation - a sort of asymptomatic run-away. That may be OK, but once its done, no one is paying for infrastructure.

Comment: Re:Sort of redundant (Score 3, Interesting) 113

The risk of large scale surveillance is that it can generate data sets that can be mined for information. Tracking can show networks of friends, attendance at political rallies, books read, movies watched, foods and alcohol consumed. Does this pattern match for a potential terrorist - can't prove anything, but maybe you shouldn't keep your job at Lockheed, or should get extra screening at the airport? Did you watch "little miss sunshine" too many times for your demographic - could mean you are a pedophile - maybe you shouldn't have a job as a school teacher - think of the children.

Which political information should you see? Candidates can target their adds to YOU specifically. Same for news, and advertising.

Maybe you don't get enough sleep, or are found to meet women ( or other men) at bars and take them home. Sounds like "statistically" you might be a health risk and your insurance rates will go up.

Large scale tracking, data collection and analysis allow for statistical pattern matches. The public might be happy that a new system has a only 1% failure rate, and only a 10% false positive rate for recognizing people who are a danger to children - unless you are in that 10%

Comment: Costs? (Score 2) 89

Mars one claims $6B to put 4 people on mars.
On one side -how do they plan to raise that amount of money? They use the Olympics as an example,but that is an event with an enormous viewership. Are they claiming they can get anything like a similar number of viewers for a bunch of guys living (or slowly dying) on mars?

On the other side, what technology do they have that makes a mars mission cost $6B, not the hundreds of billions that NASA estimates? Sure they may be able to do for somewhat less money, but a factor of 100??? Where is their demonstration of technical expertise to support such a claim?

Its just a scam.

Comment: Doesn't matter (Score 2) 385

by joe_frisch (#49289835) Attached to: Ask Slashdot: Choosing a Laptop To Support Physics Research?

I'm a career physicist, and I regularly take college interns. She can use whatever she is comfortable with. I I need my interns to have some particular computer or software I will get it for them.

Personal computers in physics are mostly for writing reports and quick calculations. High power computation and data analysis is done on dedicated server farms.The personal computer is just used as a terminal.

Comment: Re:Consistency (Score 4, Interesting) 63

by joe_frisch (#49273551) Attached to: World's Most Powerful Laser Diode Arrays Deployed

the pump is probably 3.2MW for a long pulse (100s of microseconds), and the output is petawatts for a short time (femtoseconds).Diodes are often used to pump solid state laser materials that store energy for many microseconds, then release it much more quickly. (along with chirp pulse amplification to get even larger power compression).

Humanity has the stars in its future, and that future is too important to be lost under the burden of juvenile folly and ignorant superstition. - Isaac Asimov

Working...