For Questions That Don't Merit Their Own Thread

[kerbiloid]

A little bit later the truth will reveal about the lunar race, lol.

Avoiding the unnecessary technical details of the Soviet peaceful lunar program,
the peaceful lunar LEMming of Apollo was coincidentally co-existing with Project Horizon and Project Orion (see Deep Space Bombardment Force and Orion-based ICBM) and wasn't related to a potential lunar rocket base foundation.

Obviously, only the national pride forced both parties to compete in lunar race (let alone the details of both Mercury and Vostok flights), not the desire to establish a permanent lunar base and stop the counterpart from doing that.

And of course, the Apollo program was killed in midair (with cancelling the last several flights) not because US got sure that a potential lunar military base is too hard and expensive even for them,
while the Russkies got sad that they failed to be first and scrapped the almost ready lunar rocket due to that, rather than because got ensured that the lunar military base is not possible even for US, so the topic will stay irrelevant at least for decades, and it's no need to hurry anymore.

It was just a sport race costing tens of billions for both, don't you see?

Certainly, the Outer Space Treaty is not a constatation of the fact than noone was able to capture the Moon in the foreseeable then-future, so no need in making each other's brains and look in the Moon direction for close several decades, but a demonstration of good will and peaceful intentions.

Edited August 21, 2021 by kerbiloid

[JoeSchmuckatelli]

Odd article apparently cribbed from another article... But the images are cool:

https://www.google.com/amp/s/futurism.com/triple-transit-jupiters-moons/amp

Triple transit (lunar eclipses) of Jupiter 

[JoeSchmuckatelli]

Reading a recent article about worm-hole stability got me wondering:

Would a black hole repel a negative mass star? 

 

For reference:  

https://www.space.com/traversable-wormholes-modified-gravity

Edited August 24, 2021 by JoeSchmuckatelli

[ARS]

On 8/21/2021 at 7:53 PM, kerbiloid said:

A little bit later the truth will reveal about the lunar race...

Funnily enough, Apollo Program was born because USA's previous proposal to one-up the Soviets was considered nuts, since after the Sputnik debacle, USA was desperately searching for ways to top the Soviets in the space race, and a proposal was made that an atomic bomb be detonated on the Moon (just to send a message). Fortunately, they decided to send astronauts to the moon instead after they realized the difference between legitimate science and cartoonish supervillainy

[kerbiloid]

35 minutes ago, ARS said:

USA was desperately searching for ways to top the Soviets in the space race, and a proposal was made that an atomic bomb be detonated on the Moon (just to send a message).

The same proposal was for the Soviet Luna program, for E-4 craft series.

So, looks like both parties needed to test a nuke at the airless planet surface to develop the lunar warheads, and the conquest of the Moon was meant literally.

***

And no, the lunar nuke wouldn't be invisible like the journalists say, even in vacuum.

Because at the lunar surface it will heat and melt a spot on the surface which will be definitely visible on the explosion (because hot and shiny) and after (a glassy crater).

Also, the proposals were mostly about the backside of the Moon, lol

So, nobody except the owner could see it anyway, due to lack of lunar satellites on that time.

Edited August 25, 2021 by kerbiloid

[magnemoe]

1 hour ago, kerbiloid said:

The same proposal was for the Soviet Luna program, for E-4 craft series.

So, looks like both parties needed to test a nuke at the airless planet surface to develop the lunar warheads, and the conquest of the Moon was meant literally.

***

And no, the lunar nuke wouldn't be invisible like the journalists say, even in vacuum.

Because at the lunar surface it will heat and melt a spot on the surface which will be definitely visible on the explosion (because hot and shiny) and after (a glassy crater).

Also, the proposals were mostly about the backside of the Moon, lol

So, nobody except the owner could see it anyway, due to lack of lunar satellites on that time.

Think the US idea was at the edge of that we can see, that way the explosion would have space as background not the lunar surface. The idea was that they could get spectroscopy of the surface they vaporized. 
Now aiming it would be an much larger problem, I guess it would be much easier to aim for night side who can be all of the moon. 

[ARS]

If there's no oxygen in space, does it means a corrosion will never happen on spacecraft? What about corrosion of metal by strong acid? Does it still work without oxygen?

[AHHans]

15 hours ago, JoeSchmuckatelli said:

Would a black hole repel a negative mass star? 

Yes, that's kind of the (trivial) definition of negative mass.
And "have not observed" is a way of saying "probably does not exists".

1 hour ago, ARS said:

If there's no oxygen in space, does it means a corrosion will never happen on spacecraft?

Correct as far as I think you meant the question. You will have "normal" corrosion inside the habitable parts of spacecraft, but not on parts that are exposed to the vacuum of space. What you have there instead is cold welding.

1 hour ago, ARS said:

What about corrosion of metal by strong acid? Does it still work without oxygen?

Most common acids are only actually reactive if they are in a solution in water (or so). As water tends to quickly evaporate in a vacuum I don't think this is a big issue on most spacecraft. But otherwise: yes, if you e.g. have a corrosive (and vacuum stable) grease then that will keep corroding in space.
[Edit:] Actually: I wouldn't be too surprised if some lubricants actually only become corrosive in space, e.g. due to the radiation there or because part of the lubricant evaporates.

Edited August 25, 2021 by AHHans

[StrandedonEarth]

Hmm, I wonder how aluminum would like mercury in a vacuum? It’s the oxygen that’s the problem….

[JoeSchmuckatelli]

18 minutes ago, StrandedonEarth said:

Hmm, I wonder how aluminum would like mercury in a vacuum? It’s the oxygen that’s the problem….

Thanks to you - I had to Google that... 

 

2 hours ago, AHHans said:

Yes, that's kind of the (trivial) definition of negative mass.
And "have not observed" is a way of saying "probably does not exists

Yeah - I get that - so the place to look would be in the repellers*.   Makes you wonder if a star could be negative mass whether it's light would be visible at all (as in - if it does not follow one rule, why would it follow any rule?) 

... And even - if a particle could be negative mass... Would it be attractive to other negative mass particles? Could there ever be a negative mass star??? 

(Alice - are you down there?) 

 

* https://en.m.wikipedia.org/wiki/Dipole_repeller

 

Edited August 25, 2021 by JoeSchmuckatelli

[kerbiloid]

We need a mercury planet in KSP / RSS.

Not that fake, rocky Mercury, but the real, mercury Mercury.

[JoeSchmuckatelli]

20 minutes ago, kerbiloid said:

We need a mercury planet in KSP / RSS.

Not that fake, rocky Mercury, but the real, mercury Mercury.

Yes - but could you stand on it... or would you have to swim?

[kerbiloid]

8 minutes ago, JoeSchmuckatelli said:

but could you stand on it...

Its density is 13 600 kg/m3, and its surface tension is great.

Probably, like a trampoline.

Edited August 25, 2021 by kerbiloid

[magnemoe]

12 minutes ago, kerbiloid said:

Its density is 13 600 kg/m3, and its surface tension is great.

Probably, like a trampoline.

Probably act more like mud, you sink in to some depth but as its an liquid you would be unstable if you tried to walk on it. Walking should keep you stable I guess. 
 As I understand you could run on the surface of water on the moon who would be an nice picture to send home then we build an larger moon base. 

[JoeSchmuckatelli]

For those interested in such things: a candidate 'previously unknown branch of archaic humans' may have been discovered.  A divergent or parallel population to the Denisovan humans who preceded modern humans into the SEA islands.

Genome of a middle Holocene hunter-gatherer from Wallacea | Nature

Ancient DNA from a teenage girl reveals previously unknown group of humans - CNN

 

[AHHans]

3 hours ago, StrandedonEarth said:

Hmm, I wonder how aluminum would like mercury in a vacuum? It’s the oxygen that’s the problem….

Well, oxygen is not the only problem with dropping mercury onto aluminum that you'd like to keep its shape. Without oxygen you don't get these "hairy" structures out of aluminum-oxide, but you still get mercury dissolved into the aluminum which changes its properties and e.g. makes structural aluminum very weak.

 

3 hours ago, JoeSchmuckatelli said:

Yeah - I get that - so the place to look would be in the repellers*.

Well, I would suggest to look on Pandora or other places with a good supply of unobtanium.

4 hours ago, JoeSchmuckatelli said:

Makes you wonder if a star could be negative mass whether it's light would be visible at all (as in - if it does not follow one rule, why would it follow any rule?)

Well, for a long time it was believed that antimatter might have a negative mass.^(*) If that were the case then, yes, this does interact in the same way as normal matter with the electromagnetic force, and thus emits (and absorbs etc.) visible light in the same way. However, if your negative mass is something like the Pa'anuri from Schlock Mercenary, then this wouldn't interact with our electromagnetic force and thus not be visible.

^(*) AFAIK the experiments to test that are in favor for antimatter to have normal mass.

5 hours ago, JoeSchmuckatelli said:

And even - if a particle could be negative mass... Would it be attractive to other negative mass particles?

Well, I'm not an expert on negative mass particle fashion, so I don't know. But I'd guess if they like each other well enough then they would be attracted to each other.

The thing is that our current understanding of physics makes it very unlikely that negative mass particles exist. So we could think up anything with any properties that we like.

[JoeSchmuckatelli]

1 hour ago, AHHans said:

I'm not an expert on negative mass particle fashion, so I don't know.

Lolz! 

Well played 

[kerbiloid]

The mass itself is a fiction.
It's just a(n empirical) coefficient to bind the momentum and the energy together, and to describe the local curvature of space-time continuum.
So, the question about the mass properties is itself not relevant.

A particle with negative mass will act like the reasons which make its calculated mass value negative tell her to act.

[K^2]

12 hours ago, AHHans said:

Well, for a long time it was believed that antimatter might have a negative mass.

Well, ok, I mean, it sort of does? But not in a way that makes it useful. Antiparticles behave in every way as negative mass particles traveling backwards in time, which still gives them positive inertial mass and positive energy density. So as far as things like exotic energy for warp drives, stable wormholes, and closed time loops go, it's absolutely no help. It's almost more of a mathematical quirk.

One of the problems in physics, as far as making it easy to understand to people who didn't spend years or even decades studying it, is that a lot of terms have multiple meanings depending on the exact context. And while you can be precise and reference rest mass, inertial mass, gravitational mass, etc., very often we just say "mass", and people in the field know which one you mean. Usually. It gets even worse when notations change over time. Everyone knows E=mc², and back when Einstein wrote it, that was a valid expression because m meant relativistic mass. Except in modern day physics, m usually means rest mass - Einstein would have denoted it as m₀. But because notation changed, E=mc² is no longer correct, not because of anything new in physics, we just mean a different thing by symbol m. So the correct expression would either be E=γmc², where γ is the Lorentz boost due to not being in the rest frame where m is relevant, or you would explicitly include momentum: E²=m²c⁴ + p²c². And you can see that if you flip signs of both E and m in these two equations, absolutely nothing changes. There is a more convoluted and precise explanation for why negative mass actually makes sense for antiparticles, but it involves Green's functions and functions of complex variable. Point is, mathematically, it makes sense to think of antiparticles as having a negative mass, but practically it doesn't make a difference. And the kind of mass we'd measure in an experiment, which is usually inertial mass, would still be a positive value.

[AHHans]

1 hour ago, K^2 said:

Well, ok, I mean, it sort of does? But not in a way that makes it useful. [...]

I was talking about "negative mass" in the sense that would make it useful for generating wormholes, warp drives, etc. I.e. something that "bends space-time the other way". I guess you would call that negative gravitational mass, because one effect I would expect from such an object is that it would be repelled in a gravity field.

1 hour ago, K^2 said:

And the kind of mass we'd measure in an experiment, which is usually inertial mass, would still be a positive value.

Well, the experiments that I was referring to were done at Cern and involved creating a significant amount of anti-hydrogen and then trying to figure out if it gets attracted or repelled in Earth's gravitational field.

[kerbiloid]

1 hour ago, AHHans said:

I was talking about "negative mass" in the sense that would make it useful for generating wormholes

Hehe. sqrt(-1) = i

What's a gravitational radius of a negative mass? An imaginary space? A time?

I mean, what's the speed/momentum/energy of that?

Will a particle orbiting around the negative mass black hole move in time?

[AHHans]

26 minutes ago, kerbiloid said:

I mean, what's the speed/momentum/energy of that?

That's the rabbit hole that I didn't want to get into. So my answer to that question is: The reason why I don't think that something like this actually exists.

[Lisias]

27 minutes ago, kerbiloid said:

Hehe. sqrt(-1) = i

Tachyonic fields. Imaginary (complex) Mass.

Believe it if you can.

30 minutes ago, kerbiloid said:

What's a gravitational radius of a negative mass? An imaginary space? A time?

The same of the "normal" mass. The difference would be a change on the signal of the slope of the gravity well - anti-gravity, if you prefer.

33 minutes ago, kerbiloid said:

I mean, what's the speed/momentum/energy of that?

That's beyound what I can understand, I barely handle Einstein…  

35 minutes ago, kerbiloid said:

Will a particle orbiting around the negative mass black hole move in time?

Yes, this is what the formulas say. However...

Now and then I watch a video from Sabine Hossenfelder, and there's one that appears to be relevant to these subjects.

Formulas are for Physics what Abstractions and Models are for programming - they are inherently "wrong" (in the sense they describes something by simplifying things in order to make it cope with the restrictions at hand, so they do not accurately describe the subject), but they are still useful on a finite scope of problems. Things get hairy when you start to believe that your models really match the Reality and try to apply them outside the scope they are proven to work.

As you said above, mass is an abstraction. So Einstein's E=mc² is another one (as its fundament is an abstraction itself - no theorem can be more accurate than its corollaries) that it's proven to describe pretty accurately the Reality under certain restrictions, as positive "mass" and finite density.

 

22 minutes ago, AHHans said:

<cut by me> The reason why I don't think that something like this actually exists.

That was what was said when Einstein proposed a new Gravity model, ditching Newton's.

But Einstein also said that about Quantum Physics, and evidences demonstrates that this thing work (so it appears that God really plays dice with the Universe).

So I just sit comfily on my coach and what the videos - they are so entertaining nowadays as Star Trek, if you ask me.

[JoeSchmuckatelli]

5 minutes ago, Lisias said:

I just sit comfily on my coach and what the videos - they are so entertaining nowadays

There are some really good videos out there.  Sadly most seem like they're designed so my 6th grader can understand (which is good when trying to get her excited about space) - but sometimes a duffer like me needs a bit of a deeper dive.  Those are hard to find!

 

Now - this one is quite good (about the EHT effort to image a BH, and (IIRC) Stephen Hawking's last (and less famous collaborators') paper on soft hair (attempting to solve the information paradox).

The Edge of All We Know (2020) - IMDb - its on Netflix (I think)

[kerbiloid]

What if the particle count is negative?

Let's take -1 particle of normal mass.

What gravitational field will it cause?