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Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

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Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#151

Post by salty_biscuits »

ISL wrote: post #128
salty_biscuits wrote: post #111

Earlier quoted context omitted.

"GPS is impossible without corrections from both special relativity and general relativity" I appreciate your comments in general, but I feel that this point needs to be tempered. Yes there are corrections due to SR and GR effects in GNSS, but they tend to get lost in the morass of the least squares residuals compared to all the other much bigger effects, like clock errors, orbital errors, ionosphere delays, etc, etc…

The relativistic corrections are cumulative (and, if I recall correctly, have opposite sign!). Without correcting for the shifts, it is my understanding that GPS would be degraded within minutes and useless in less than a day. http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5253894/

You have to correct for the shifts, but no knowledge of relativity is required (maybe the SR correction is put in analytically but GR is definitely not). The least squares problem deals with it by lumping it with all the other time offsets for the pseudoranges for each satellite. And of these it is a small part of the error budget and is dealt with by averaging multiple measurements.

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#152

Post by gizmo686 »

duchenne wrote: post #61

I love the following Feynman's quote: ``In those days, one of the theories proposed was that the planets went around because behind them were invisible angels, beating their wings and driving the planets forward. You will see that this theory is now modified! It turns out that in order to keep the planets going around, the invisible angels must fly in a different direction and they have no wings. Otherwise, it is a s…

> At that time, it was making people crazy to think that an object could remotely affect another one. Now, people just accept it. But, when you think about it, it really sounds magic.

Do people (read physisicts) accept this. My understanding is that, while unconfirmed, the graviton is still a respectable hypothesis.

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#153

Post by jbattle »

cartoonworld wrote: post #142
jbattle wrote: post #34

Earlier quoted context omitted.

I've never understood why "paradoxes make cause-and-effect-reasoning difficult" concerns are a valid argument that something could not be possible. Does physics care whether the workings of the universe are accessible to our logic?

If I look at a random numeric oracle of 1-10, and consider the result as N, and apply to it some kind of mathematical formalism of: If ( N + 10 = 20 ) then eat(last_bagel) My wife comes home and is cross with me for eating the last_bagel. So, I hop in my handy time machine, travel back to before the time where I access the oracle, and alter it to only produce a random number from 1-9. If I succeed, my wife is no long…

Yet quantum mechanics is full of phenomenon that operate counter to our understanding of cause and effect. Physicists accept things like double slit interference - why do they seem to consider these time travel induced causal paradoxes so off-limits?

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#154

Post by ISL »

salty_biscuits wrote: post #151
ISL wrote: post #128

Earlier quoted context omitted.

The relativistic corrections are cumulative (and, if I recall correctly, have opposite sign!). Without correcting for the shifts, it is my understanding that GPS would be degraded within minutes and useless in less than a day. http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5253894/

You have to correct for the shifts, but no knowledge of relativity is required (maybe the SR correction is put in analytically but GR is definitely not). The least squares problem deals with it by lumping it with all the other time offsets for the pseudoranges for each satellite. And of these it is a small part of the error budget and is dealt with by averaging multiple measurements.

The second reference cited above includes the passage:

"There is an interesting story about this frequency offset. At the time of launch of the NTS-2 satellite (23 June 1977), which contained the first Cesium atomic clock to be placed in orbit, it was recognized that orbiting clocks would require a relativistic correction, but there was uncertainty as to its magnitude as well as its sign. Indeed, there were some who doubted that relativistic effects were truths that would need to be incorporated [5]! A frequency synthesizer was built into the satellite clock system so that after launch, if in fact the rate of the clock in its final orbit was that predicted by general relativity, then the synthesizer could be turned on, bringing the clock to the coordinate rate necessary for operation. After the Cesium clock was turned on in NTS-2, it was operated for about 20 days to measure its clock rate before turning on the synthesizer [11]. The frequency measured during that interval was +442.5 parts in 10^12 compared to clocks on the ground, while general relativity predicted +446.5 parts in 10^12. The difference was well within the accuracy capabilities of the orbiting clock. This then gave about a 1% verification of the combined second-order Doppler and gravitational frequency shift effects for a clock at 4.2 earth radii."

It makes sense that offset corrections can be handled by a lumped model, as any relativistic corrections on timescales longer than an orbit will be constants of the satellite orbit. Making sub-orbit-duration corrections might require a model that captures more of the relevant physics.

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#155

Post by poelzi »

conscion wrote: post #150
poelzi wrote: post #132

Earlier quoted context omitted.

Physics took 2 wrong roads and it got stuck in a local minima of the truth plane. Understanding that physics is the most ignorant field of science and how proud the field is of it's models, I don't think this will come anytime soon. https://www.pnas.org/content/112/24/7426 PS: you need to understand how gravity is derived to manipulate it's propagation. Since the mechanisms are very stable due various reasons, only a…

What's your physics model?

This one: https://www.amazon.de/Basic-Structures-Matter-Supergravitati...

Never could have come up with such a brilliant theory, took me a year to understand it. Now I understand 137 ^^

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#156

Post by cartoonworld »

jbattle wrote: post #153
cartoonworld wrote: post #142

Earlier quoted context omitted.

If I look at a random numeric oracle of 1-10, and consider the result as N, and apply to it some kind of mathematical formalism of: If ( N + 10 = 20 ) then eat(last_bagel) My wife comes home and is cross with me for eating the last_bagel. So, I hop in my handy time machine, travel back to before the time where I access the oracle, and alter it to only produce a random number from 1-9. If I succeed, my wife is no long…

Yet quantum mechanics is full of phenomenon that operate counter to our understanding of cause and effect. Physicists accept things like double slit interference - why do they seem to consider these time travel induced causal paradoxes so off-limits?

Mostly because a bagel is not an electron, and slit experiments illustrate wave-particle duality, do they not?

Anyhow, the message was about how paradoxes make reasoning hard, not about how we can wave away the uncertainties. Next time I'll just skip all the time machine nonesense and head to the nearest rectory.

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#157

Post by ISL »

raattgift wrote: post #95
ISL wrote: post #51

Earlier quoted context omitted.

That's a great and important question. (doubly so for me, as constrained resources may see me leave the field, to which I have devoted my entire professional life, in the coming months) We are perennially grateful for the support we receive to do the work that we do. To a high degree of approximation, Einstein's predictions are very, very correct. We are trying to look very carefully at Nature because we don't think…

> constrained resources may see me leave the field I am sorry to hear that - it will be a loss for Eöt-Wash.

I'm super bummed about it. It is a complicated story involving impedance mismatches between the goals of two administrative silos. The high-level goals are the same (good science, students, technology), but there are structural differences on how to get there...

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#158

Post by pdonis »

mr_mitm wrote: post #59
pdonis wrote: post #24

Earlier quoted context omitted.

> Physics, as currently understood from available experimental evidence, 100% allows time travel to the past, paradoxes included. General Relativity, which is where the term "closed timelike curve" is used, does not allow paradoxes. A spacetime with closed timelike curves in it (for example, the Godel universe) still has only one thing happening at each event. The real problem conceptually with such solutions is that…

> you cannot freely choose what to do But that's already the case. It could be my free will to walk on the ceiling, but the laws of physics won't let me.

Yes, and in the case of a closed timelike curve, the laws of physics won't let you do something different the second time you are at a particular event in spacetime than you did the first time. Both are straightforward constraints from the point of view of the laws of physics.

But that still does not mean they look the same to us, intuitively speaking. For example, the laws of physics won't let you walk on the ceiling at all, whether your worldline is a closed timelike curve or not. But if your worldline is not a closed timelike curve, then, intuitively, it seems like the laws of physics will let you choose which direction you want to walk on the floor. However, if your worldline is a closed timelike curve, and you come around again to the event in spacetime where you chose to walk to the left last time around, the laws of physics will not let you choose to walk to the right this time; they constrain you to walk to the left again, since from the standpoint of the laws of physics you are at the same event in spacetime and that event can only happen one way. To many people that seems like a much stronger constraint than the constraint that you can't choose to walk on the ceiling.

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#159

Post by garmaine »

cartoonworld wrote: post #156
jbattle wrote: post #153

Earlier quoted context omitted.

Yet quantum mechanics is full of phenomenon that operate counter to our understanding of cause and effect. Physicists accept things like double slit interference - why do they seem to consider these time travel induced causal paradoxes so off-limits?

Mostly because a bagel is not an electron, and slit experiments illustrate wave-particle duality, do they not? Anyhow, the message was about how paradoxes make reasoning hard, not about how we can wave away the uncertainties. Next time I'll just skip all the time machine nonesense and head to the nearest rectory.

I think the point made by user jbattle is that physics already allows, for example, causal relationships that go either “back in time” or “faster than light” from certain valid reference frames. Physicists have found ways of coping with this reality. Why should the introduction of a time machine make it fundamentally any different?

Re: Military Has Been Researching "Anti-Gravity" For Nearly 70 Years

#160

Post by sgt101 »

de_watcher wrote: post #82
rurban wrote: post #70

Earlier quoted context omitted.

Gravity is very similar to magnetism, a "magically" attracting force of distinct objects. The explanation is very easy via fields. Just trying to explain it via particles will get you into trouble, e.g. the flawed standard model, or the Higgs. Einstein was pretty close in his spacetime bending explanation, but this still doesn't explain dark matter or the recent gravity experiments with fast rotating magnets in stron…

> Gravity is very similar to magnetism But magnets, how do they work? (C)

When I was at uni my mother had a job as a nursery school teacher. One of the projects they did was to look at forces (quite good really!) So, they pulled ropes, and dropped apples, and sailed boats and used magnets. She asked me to think of a simple explanation of how the magnets worked so that the children could understand them. It is painful to me that I could not do that, and I can't do it now and I believe that no one can!
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