Military Has Been Researching "Anti-Gravity" For Nearly 70 Years • Hacker News Board

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

#21

Post by garmaine » Thu, Oct 31, 2019, 4:32 AM UTC

kiba wrote: post #6

GuiA wrote: post #4

If you do not work on an important problem, it's unlikely you'll do important work. It's perfectly obvious. Great scientists have thought through, in a careful way, a number of important problems in their field, and they keep an eye on wondering how to attack them. Let me warn you, `important problem' must be phrased carefully. The three outstanding problems in physics, in a certain sense, were never worked on while…

Time travel back into the past is understood to be impossible.

Physicist here (by degree, not profession). What you state is not true: by currently accepted physical theories, time travel to the past IS very much possible. It's known as a "closed, time-like curve" in the literature. Now, most mechanisms explored for doing so wouldn't allow travel back further than the initial creation of the time travel device, so you could say that time travel to our past is not possible since the construction of such a thing is necessarily in the future. But as a matter of physics, general relativity allows it.

Now that said, most physicists are convinced that time travel cannot be possible, because if it were then paradoxical situations could be constructed--e.g. going back in time and killing yourself (the earlier you) before you entered the machine, or killing your grandfather before your father was born, etc. There are as many theorized rules preventing or limiting time travel as there are physicists that have looked at it, but critically they are all ADDITIONAL rules, postulated not to explain observable phenomenon but purely to think up a way time travel paradoxes might be avoided. Physics, as currently understood from available experimental evidence, 100% allows time travel to the past, paradoxes included.

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

#22

Post by trhway » Thu, Oct 31, 2019, 4:56 AM UTC

garmaine wrote: post #21

kiba wrote: post #6

Earlier quoted context omitted.

Time travel back into the past is understood to be impossible.

Physicist here (by degree, not profession). What you state is not true: by currently accepted physical theories, time travel to the past IS very much possible. It's known as a "closed, time-like curve" in the literature. Now, most mechanisms explored for doing so wouldn't allow travel back further than the initial creation of the time travel device, so you could say that time travel to our past is not possible since…

> then paradoxical situations could be constructed--e.g. going back in time and killing yourself (the earlier you) before you entered the machine, or killing your grandfather before your father was born

Can't the paradox be resolved by considering it as a fork/branching of a new reality/timeline where the grandfather is killed, kind of similar to many world interpretation in QM. I'd speculate that using model of lazy fork it may be possible to get some ballpark estimates on energy requirements/etc. below the typical "all the energy in the Universe". Such forks/perturbations possibly also dissipate, like a small wave in the pond, and the forked reality gets naturally merged into the mainline ( i think this is how QM's many world while possibly true is still compatible with "realistic" situation of limited number, may be even just 1, Universe mainlines)

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

#23

Post by pdonis » Thu, Oct 31, 2019, 4:56 AM UTC

garmaine wrote: post #21

kiba wrote: post #6

Earlier quoted context omitted.

Time travel back into the past is understood to be impossible.

Physicist here (by degree, not profession). What you state is not true: by currently accepted physical theories, time travel to the past IS very much possible. It's known as a "closed, time-like curve" in the literature. Now, most mechanisms explored for doing so wouldn't allow travel back further than the initial creation of the time travel device, so you could say that time travel to our past is not possible since…

> by currently accepted physical theories, time travel to the past IS very much possible

Only if you make use of exotic matter, which nobody has ever observed and which there are good reasons to think cannot exist.

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

#24

Post by pdonis » Thu, Oct 31, 2019, 4:59 AM UTC

garmaine wrote: post #21

kiba wrote: post #6

Earlier quoted context omitted.

Time travel back into the past is understood to be impossible.

Physicist here (by degree, not profession). What you state is not true: by currently accepted physical theories, time travel to the past IS very much possible. It's known as a "closed, time-like curve" in the literature. Now, most mechanisms explored for doing so wouldn't allow travel back further than the initial creation of the time travel device, so you could say that time travel to our past is not possible since…

> 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 they appear to contradict free will: since only one thing can happen at each event, if you experience visiting that event multiple times, you cannot freely choose what to do at that event.

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

#25

Post by cartoonworld » Thu, Oct 31, 2019, 5:00 AM UTC

garmaine wrote: post #21

kiba wrote: post #6

Earlier quoted context omitted.

Time travel back into the past is understood to be impossible.

Physicist here (by degree, not profession). What you state is not true: by currently accepted physical theories, time travel to the past IS very much possible. It's known as a "closed, time-like curve" in the literature. Now, most mechanisms explored for doing so wouldn't allow travel back further than the initial creation of the time travel device, so you could say that time travel to our past is not possible since…

Regarding the time paradoxes, the second part of your comment reminded me of a very interesting (and good) 1977 Czech film called "Tomorrow I'll Wake Up and Scald Myself with Tea"[0], in which some Nazis survive WWII. They get ahold of some anti-aging pills, and after centuries, hijack a time machine back to World War II in order to give Hitler the bomb, reversing the course of the war. However, their efforts are repeatedly stymied by comical time paradoxes.

[0] https://en.wikipedia.org/wiki/Tomorrow_I'll_Wake_Up_and_Scal...

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

#26

Post by jacobreg » Thu, Oct 31, 2019, 5:01 AM UTC

mLuby wrote: post #2

There are Gravity Stones from the 60's scattered among US colleges to > "remind students of the blessings forthcoming when a semi-insulator is discovered in order to harness gravity as a free power and reduce airplane accidents" Decent way to get students thinking about it. https://en.wikipedia.org/wiki/Gravity_Research_Foundation#Mo...

Oh the story behind that is a wild ride from start to finish. Babson's sister drowned when they were children, and he decided the real reason that happened is anti-gravity technology wasn't sufficiently advanced to prevent her drowning. He spent a large amount of his philanthropy funding anti-gravity research for the rest of his life.

Edit: Just realized this is mentioned in the article you linked.

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

#27

Post by ISL » Thu, Oct 31, 2019, 5:02 AM UTC

Physicists have been searching for variations in the coupling of materials to gravity for more than a century, and by some measure, for more than a millenium.

https://en.wikipedia.org/wiki/Equivalence_principle#Tests_of...

Every experiment anyone has ever tried has come up empty. The equivalence principle is a postulate (Einstein's "happiest idea") that underlies General Relativity, making it essential to test.

(Source: This is literally what I do for a living.)

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

#28

Post by ekianjo » Thu, Oct 31, 2019, 5:07 AM UTC

ozzmotik wrote: post #20

ekianjo wrote: post #10

Earlier quoted context omitted.

And where would the information about parallel universes be contained?

i would figure in that parallel universe lol, or if you want to be more general, in some overarching metaversal container leading out to the omniverse at greeter degrees. but that's just me ¯\_(ツ)_/¯

So the universe would be composed of infinite energy?

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

#29

Post by bonestamp2 » Thu, Oct 31, 2019, 5:08 AM UTC

danschumann wrote: post #18

To really be able to manipulate gravity, you would also need to manipulate mass, and so far nuclear is the only way I know of, in which we do that, but uhh.. I don't think we'll get anti gravity until we can control mini stars... Little nuclear engines.

What if gravity isn't always relative to mass? I mean, all of our scientific evidence suggests it is... but I suppose it's possible that's not quite right.

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

#30

Post by adrianN » Thu, Oct 31, 2019, 5:09 AM UTC

pdonis wrote: post #24

garmaine wrote: post #21

Earlier quoted context omitted.

Physicist here (by degree, not profession). What you state is not true: by currently accepted physical theories, time travel to the past IS very much possible. It's known as a "closed, time-like curve" in the literature. Now, most mechanisms explored for doing so wouldn't allow travel back further than the initial creation of the time travel device, so you could say that time travel to our past is not possible since…

> 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…

Luckily "free will" as would fit a layman's interpretation of the term is already incompatible with physics, so the existence of CTCs doesn't pose additional problems.