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Old June 5 2013, 06:29 PM   #87
FlyingLemons
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Re: Strange Dark Matter Theory

Crazy Eddie wrote: View Post
His reply was exactly this: GPS satellites do not really account for relativistic effects because they don't have to: their onboard clocks re-synch periodically through ground stations to keep them coordinated with both the Earth clocks and one another.
That's the GPS system recalibrating the satellite clock from the ground station to take into account the time dilation that would occur if the satellite clock were left to its own devices. It suppresses the time dilation effect by design - but without this built in would have problems as is well documented in the literature. Plenty of experiments have been done using the GPS system to examine the time dilation effect in general relativity, and thus we regard it as generally uncontroversial.

But I digress. I didn't read the rest of the thread...

Crazy Eddie wrote:
Theoretical physicists have become so enamored by the possibilities of dark matter that derivative theories about what it could be and what it could DO extend far beyond any logical connection to the data that suggests its existence...
Uh... not really. The media would like to portray it that way, but in actual fact there are quite a few interesting debates going on surrounding that area.

Crazy Eddie wrote: View Post
If a highly respected physicist hacks together a bullshit mathematical equation that no one understands, who exactly is going to call him on it? Not his peers, who don't understand the equation and can't explain why it's bullshit.
Have you ever tried submitting a paper to Nature, PRD or JHEP? The reviewers there tend to be absolutely merciless if they find a mistake in your math - in my experience papers need to be mathematically watertight to get through at least for those journals. As iguana pointed out, physicists are pretty cut-throat and don't shy away from criticizing each other's work.

Crazy Eddie wrote: View Post
The only reason scientists question modified gravity is because they're uncomfortable with the idea that general relativity may be at least partially incorrect and/or inapplicable.
Theoretical physicist perfectly comfortable with the idea of modified gravity here...

Crazy Eddie wrote: View Post
Relativity itself has become a kind of academic sacred cow that scientists and engineers are reluctant to give the appearance of questioning, even when the theory itself is legitimately inapplicable.
Uh, what? Where'd you pick this up? There's plenty of us thinking about modifications and extensions to the theory of relativity because of the wealth of observational data in particle physics and cosmology telling us that something's not quite right with regards to the cosmological constant and high-energy behavior of gravity.

I'm a particle physicist so my interests lie towards the smaller areas of physics rather than the large, but off the top of my head:

There's the idea of inhomogeneous cosmologies that's been knocking about for ages and still generates papers. If the universe is not homogeneous and isotropic, perhaps dark matter doesn't exist after all and is instead an observational consequence of inhomogeneity.

Modified gravity, often involving scalar fields. Up until recently, I might have said "where's your scalar field?". There's now something vaguely Higgs-like floating around in LHC results... possibly we've found the first instance of a scalar field in nature.

Then there's one area I've worked in: that of the application of renormalization group. RG allows the constants of a quantum field theory to become subject to an energy scale, and allows us to vary said constants and study how the phenomenology of the system is affected by this.

Applying it to gravity, you can treat the theory of general relativity as an effective field theory and allow G and lambda to vary from the Planck era. This is quite interesting as some work by Percacci indicates that we could get inflation, reheating and the cosmological constant for "free" rather than through the introduction of new, unknown scalar fields.

Some also think that this idea could again be responsible for dark matter as well, meaning that it's down to a quantum gravity effect rather than any kind of new particle out there.

Relativity isn't "sacred". Any of these three ideas being experimentally proved would cause the textbooks to be rewritten. However, there's definitely a lot of general relativity that is well-tested, and what some call "gaping holes" for some reason most of us who work in physics call research areas to be explored rather than things that have us "worried".
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