My Take on the UFO Craze Hitting Us Now

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Chap
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Re: My Take on the UFO Craze Hitting Us Now

Post by Chap »

doubtingthomas wrote:
Fri Jun 18, 2021 6:27 pm
Actually it is possible to travel thousands of light years in just a few years without the need of a wormhole tech.
https://www.npr.org/2021/06/04/10034210 ... ight-by-15
https://arxiv.org/abs/1507.06663
The first link took me too:

The FDA Has Approved An Obesity Drug That Helped Some People Drop Weight By 15%

The conclusion of the paper to which the second link takes me says:
7. Conclusions
The Relativistic Planck's Law, the Relativistic Wien's Displacement Law, and the Relativistic Stefan-Boltzmann Law have been established in inertial and non-inertial reference frames by invoking the inverse temperature 4-vector, 4-acceleration, relativistic beaming, Doppler shifting, and, when required, the appropriate proper time derivatives. In the low velocity limit of the relativistic blackbody spectrum, the corresponding and well-established stationary blackbody spectrum has been shown to emerge for each of the aforementioned relativistic laws. The Relativistic Wien's Displacement Law was shown to be independent of temperature inflation and entirely dependent on Doppler shifting. In each case, the high velocity limit of the relativistic blackbody spectrum produced the expected zero or infinite outcome.

The angular periodicity of the Relativistic Planck's Law was determined, and further work needs to be done to elucidate the emergent picture. The relativistic versions of Planck's Law, Wien's Displacement Law, and the Stefan-Boltzmann Law were compared to the stationary versions, and it was determined that only in the case of spectral radiance are there non-trivial solutions by which the descriptions produce equal results.
Somehow your point does not seem to emerge very clearly from those references. Remember, we need then-destructive translation of organised material structures at faster than light speeds. Maybe you can clarify how that emerges from the references you give?
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Re: My Take on the UFO Craze Hitting Us Now

Post by doubtingthomas »

Chap wrote:
Fri Jun 18, 2021 7:03 pm
doubtingthomas wrote:
Fri Jun 18, 2021 6:27 pm
Actually it is possible to travel thousands of light years in just a few years without the need of a wormhole tech.
https://www.npr.org/2021/06/04/10034210 ... ight-by-15
https://arxiv.org/abs/1507.06663
The first link took me too:

The FDA Has Approved An Obesity Drug That Helped Some People Drop Weight By 15%
Sorry. https://www.youtube.com/watch?v=b_TkFhj9mgk
"I have the type of (REAL) job where I can choose how to spend my time," says Marcus. :roll:
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Re: My Take on the UFO Craze Hitting Us Now

Post by doubtingthomas »

Chap wrote:
Fri Jun 18, 2021 7:03 pm
Somehow your point does not seem to emerge very clearly from those references. Remember, we need then-destructive translation of organised material structures at faster than light speeds. Maybe you can clarify how that emerges from the references you give?
Here is a better link. Time slows down when you travel close to the speed of light.
https://www.technologyreview.com/2019/1 ... ce-travel/
"I have the type of (REAL) job where I can choose how to spend my time," says Marcus. :roll:
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Re: My Take on the UFO Craze Hitting Us Now

Post by Chap »

doubtingthomas wrote:
Fri Jun 18, 2021 7:11 pm
Chap wrote:
Fri Jun 18, 2021 7:03 pm
Somehow your point does not seem to emerge very clearly from those references. Remember, we need then-destructive translation of organised material structures at faster than light speeds. Maybe you can clarify how that emerges from the references you give?
Here is a better link. Time slows down when you travel close to the speed of light.
https://www.technologyreview.com/2019/1 ... ce-travel/
Oh - that's what you mean.

Yes, IF (and that is a very big if) you can travel relative to me at a speed that was an appreciable fraction of the speed of light, your clock would run much slower than mine, so a there and back journey from my planet to earth that took several centuries from my point of view would take much less time from yours. But by the time you got back there would be nobody who knew or cared why you had gone, and everyone you knew or cared about would be long dead, so why would anybody bother?

And as I said, the whole thing depends on you being able to reach speeds comparable with 3*10exp8 m/s.
Last edited by Chap on Fri Jun 18, 2021 8:20 pm, edited 1 time in total.
Maksutov:
That's the problem with this supernatural stuff, it doesn't really solve anything. It's a placeholder for ignorance.
Mayan Elephant:
Not only have I denounced the Big Lie, I have denounced the Big lie big lie.
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Re: My Take on the UFO Craze Hitting Us Now

Post by Gadianton »

Here is a better link. Time slows down when you travel close to the speed of light.
that's misleading since velocity is relative. the spaceship views itself at rest and measures a time and space contraction for the earth, which is what's moving toward the spaceship. The benefits of slowing down for one frame with respect to another only come with acceleration.
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Re: My Take on the UFO Craze Hitting Us Now

Post by Physics Guy »

I sometimes give out homework problems related to this.

Passengers don't want to spend years under high acceleration, and they can't survive even a short burst of very high acceleration, so I figure that a reasonable benchmark is to assume a spacecraft traveling at constant acceleration—as measured by the passengers*—of around 1g. Then it's convenient to interpret "around 1g" as "exactly lightspeed-per-year", since by coincidence the two figures are quite close**.

If you want to travel someplace, you don't want to fly past it at close to the speed of light, so you should reverse the direction of acceleration half-way, to slow down to a reasonable speed by the time you arrive.

This allows some conveniently simple rules of thumb*** for relativistic space travel. Anyone geeky enough to care about this problem at all may appreciate having such simple rules that are nonetheless accurate.

1) The good news: time versus distance
Once the voyage is going to take more than a few years of passenger time, the exact formula for duration in passenger years becomes well approximated by T = 2 Ln(L), where T is the duration in years (as experienced by the passengers) and L is the distance covered, in light-years. Ln is the natural logarithm, log to the base "e", so these numbers are always going to be a few times bigger than the base 10 logarithm.

To put it another way around, after T passenger years at constant acceleration of c/year, the passengers will be able to reach a point e^{T/2} light-years away. Exponential growth is great; anywhere in our galaxy would be reachable within a decade or two at most, and distant galaxies could be reached within a human lifetime, under comfortable acceleration. The passengers would have to bid farewell forever to everyone as they leave, because everyone they knew will have been long dead before they can return, but people who merely crossed an ocean in previous centuries often knew that they would never see folks in the old country again. It's not the leaving of Liverpool that grieves me, but darling when I think of thee.

2) The bad news: energy costs
The nasty part, though, is the energy it is going to take to sustain that comfortable acceleration long enough to reach those crazy high speeds. For the convenient case of constant acceleration at c/year, the total energy cost for the trip is going to be exactly Mc^2 per light year covered, where M is the mass of your spacecraft. The really bad news is that for M of one tonne, Mc^2 is about the current annual energy consumption of the entire human species (about 10^20 Joules).

So we could send a ship 100 LY away, and the crew would only age a few years on the trip, but to do that we'd have to save up all our energy for a century—and that's just to send a cramped little capsule weighing only one tonne including all cargo. If we want to send a ten-tonne craft, so that the people don't go crazy en route and can do something once they arrive, we'll have to save up energy for a millennium.

And that doesn't even work, because we have no way of storing that much energy onboard the spacecraft without taking up a lot more mass, which also has to be carried and therefore raises the energy cost further. Even fusion power is less than 1% mass-efficient, meaning that it takes over 100 Tonnes of hydrogen to deliver Mc^2 for an M of one tonne.

In conclusion, therefore, no, there is no currently foreseeable human capability of relativistic space travel, because we can't spare anywhere near enough energy.

(*Yes, you can have an acceleration in your own frame of reference even though by definition your velocity in your own frame is zero. It's the "g-force" that you feel when you stomp on the gas in your car.)

(**No, just because your proper acceleration is c/year doesn't mean that you will reach lightspeed in one year and then go on to double lightspeed after two years. It's just a measure of inertial force, the "g-force" effect of acceleration, and it happens that c/year is close to the 9.8 m/s^2 that we feel from gravity on the surface of the Earth.)

(***In case anyone's curious, the exact expressions for travel at constant proper acceleration "a" are t = (c/a) sinh(at'/c) and x = (c^2/a)[cosh(at'/c)-1], where cosh and sinh are the hyperbolic cosine and sine functions, t' is the time as measured by the passengers, and x and t are the positions and times of the spacecraft in the frame of Earth. So if we take a = c/year and measure times in years and distances in light years, we just have t = sinh(t'), x = [cosh(t') -1]. The hyperbolic cosine is cosh(t') = (e^t' + e^{-t'})/2, so once t' is large enough that e^{-t'} becomes negligibly tiny in comparison with e^t', we have x = e^{t'}/2 to a good approximation. If we want to get to x = L/2 at the half-way mark t' = T/2, then we'll have approximately L = e^{T/2}.

The speed of the spacecraft in the Earth frame is (dx/dt) = (dx/dt')/(dt/dt') = c tanh(at'/c), which approaches c but never reaches it. So in the Earth frame the spacecraft's acceleration gets steadily less and less as the speed approaches c, but in the passengers' frame the g-force sqrt{(d^2x/dt'^2)^2-c^2(d^2t/dt'^2)^2} = a remains steady.

The relativistic kinetic energy of the spacecraft at its highest speed, attained at the half-way point t' =T/2, is Mc^2[1/sqrt{1-v^2/c^2} - 1] = Mc^2[cosh(T/2)-1] with a = c/year and time measured in years. Since that factor [cosh(T/2)-1] is exactly the position x at half-time, when position is measured in light-years, and this is exactly half the total distance, L/2, there is a conveniently simple relationship between distance and energy. It's going to cost exactly as much energy to decelerate again on the second half of the journey, so the total energy needed is going to be Mc^2 L when L is in light-years.

I have completely ignored the problem of exactly how this spacecraft is going to accelerate itself. There are no rails in space, so it's going to have to work like a rocket somehow, and this will no doubt raise the mass overhead further.)
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Re: My Take on the UFO Craze Hitting Us Now

Post by Gunnar »

In fact, isn't it also true that just the total mass of propellant required to propel a spaceship of even a relatively modest mass (along with the propellent it needs to carry) to any appreciable destination elsewhere in the galaxy at at nearly the speed of light would likely be comparable to or even exceed the entire mass of the known universe? This is why the idea that these UAPs or UFOs are interstellar spaceships is so wildly improbable, unless almost everything we think we know about general relativity is wrong. We know that can't be the case because so much of the modern technology, including, in particular, GPS navigation that we now take for granted, could not work as spectacularly well as it does if general relativity and quantum mechanics were not very close to the truth. They may not be the absolutely complete truth (and probably aren't), but it seems impossible or, at least, highly improbable, that they will ever be completely overturned by anything else.

Yet, I can't help retaining the (probably irrational) wish that there really were some as yet undiscovered and practical way to circumvent the limitations imposed by general relativity, such as a combination of anti-gravity or reactionless field drive and Alcubierre warp drive, or equivalent, and/or somehow tapping into unlimited zero point energy that would make it all possible.

If it ever becomes, despite all odds, unequivocally established that UFOs are really interstellar vehicles of some incredibly advanced extraterrestrials, then there really must be such a way, and it couldn't be all that difficult if we are really getting as many interstellar visitors as some like to claim we are.
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Re: My Take on the UFO Craze Hitting Us Now

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Gunnar wrote:
Mon Jun 28, 2021 7:02 pm
In fact, isn't it also true that just the total mass of propellant required to propel a spaceship of even a relatively modest mass (along with the propellent it needs to carry) to any appreciable destination elsewhere in the galaxy at at nearly the speed of light would likely be comparable to or even exceed the entire mass of the known universe?
I don't think it's that bad, unless you take an extreme definition of "nearly the speed of light." For sufficiently small x, the kinetic energy of an object of any non-zero mass moving at speed (1-x)c can be as large as you want, without limit. You can make it bigger than the rest energy of the known mass in the universe, if you just choose x to be really, really small. But there's no need to reach such extreme speeds. I'm willing to take several hours to fly to another continent; people used to be willing to sail for weeks or months. I don't think we need to make the Andromeda Galaxy before lunch.

I don't want to take the time to think about relativistic rocket propulsion, I'm afraid, but here is a website that I think is probably reliable. It estimates some alarmingly large fuel masses for traveling long distances, but none of the estimates is even close to the mass of the Earth. The issue of efficiency is serious, though; if you can't cash out almost all of the rest energy of your fuel into thrust, you're going to need a lot more fuel—and then you'll need more fuel to accelerate all that fuel—so you'll need even more fuel—and so on. Maybe with pessimistic assumptions for fuel efficiency you can get up to some insanely high fuel masses.

Antimatter-matter annihilation reactions might well be good enough to avoid that, in principle, but we can't just dig up antimatter. We have to contribute all that energy, at some point, to produce the antimatter. So the total energy cost of relativistic space travel is likely to be economically prohibitive for the even dimly foreseeable future, I think.

Another kind of power technology that has occurred to me, that I haven't seen written up anywhere though it very well could be, is what I've been calling the "Hawking furnace". If Stephen Hawking was right about black hole radiance then one could in principle trap a small black hole and use its hot glow to make a photon rocket, while steadily feeding matter into the black hole to stop it from evaporating away. In effect it would be like having a good ol' steam engine and shovelling coal into it, but using the Hawking process instead of combustion. If that were actually possible in principle, it would still be tricky in practice because it would be inherently unstable. If your tame black hole should happen to overheat a bit, it would start getting hotter and hotter until it blew up; if it should happen to cool down a bit, it would get colder and colder until you lost thrust. You could correct this, paradoxically by pouring in fuel to cool the hot black hole down or choking the fuel back to make it warm up. But you'd really have to keep on top of it. This scenario assumes the ability to create and control small black holes, as well as Hawking's theory being correct, so it's a pretty distant prospect at best. I like the idea of plowing through space by shovelling coal into a roaring black hole, though. It wouldn't even have to be coal. You could use table scraps.

Warp drives and wormholes might actually be more likely; we can see how they could hypothetically exist as geometries of spacetime but if General Relativity is really right then they would require forms of matter and force that we suspect may be impossible even in principle. If wormholes and warp drives don't turn out to be completely impossible, though, they may conceivably turn out to be easier than moving at high speeds in the ordinary sense of moving. And they would have the advantage of letting you go to a distant place and still come back and see your friends.
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Re: My Take on the UFO Craze Hitting Us Now

Post by DrW »

Physics Guy,

Thank you for your technical contributions to this discussion, especially for your earlier tutorial on some of the math and physics of relativistic travel. Relativity continues to delight.

Aside from the propulsion energy problem, there is another consequence of relativistic speed travel that I have not seen mentioned yet on this thread. That consequence is the fact that even in the vacuum of interstellar space, a near light speed spaceship would encounter enough gas and dust particles at high enough velocity that the collective energy of such collisions would eventually ablate or melt pretty much any available material. Ablation and melting are already a problem at 0.2c. https://iopscience.iop.org/article/10.3 ... 357/aa5da6

Many of the reports of flying saucers claim that they are spinning. One can imagine that constant rotation would distribute the craft/particle collision energy around the perimeter (constantly changing leading edge) of the craft reducing heating and ablation and thus increasing the speed that they could safely travel in space.
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Re: My Take on the UFO Craze Hitting Us Now

Post by Gunnar »

Physics Guy wrote:
Tue Jun 29, 2021 8:26 am

Warp drives and wormholes might actually be more likely; we can see how they could hypothetically exist as geometries of spacetime but if General Relativity is really right then they would require forms of matter and force that we suspect may be impossible even in principle. If wormholes and warp drives don't turn out to be completely impossible, though, they may conceivably turn out to be easier than moving at high speeds in the ordinary sense of moving. And they would have the advantage of letting you go to a distant place and still come back and see your friends.
Thanks for all your helpful input and clarification on this subject. I am obviously no scientist, just a highly interested and slightly more scientifically literate than average layman, but what you said fits well with what limited understanding of these subjects I have already managed to acquire. Thanks for adding significantly to my understanding of these issues! The more I learn about science and how the world works, the more obvious it seems to me that actual travel through ordinary space at relativistic speeds at high fractions of C is so difficult and improbable that we can pretty much safely rule out the possibility that UFOs are interstellar alien spacecraft, unless such things as warp drives, wormholes, real artificial gravity, reactionless field drives, etc. really are possible and achievable.
No precept or claim is more suspect or more likely to be false than one that can only be supported by invoking the claim of Divine authority for it--no matter who or what claims such authority.
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