For Questions That Don't Merit Their Own Thread

[Diche Bach]

13 hours ago, magnemoe said:

.5c forget anything outside of antimatter and laser pumped sails and that is for an flyby. For slowing down you need something reactionless or better as in warp or other stuff who breaks physic more than an reactionless drive. 
Yes you might manage to do this with an probe with an dyson swarm, but that is not near future  
Its not about cost or simply scale up technology to an insane level. Easy stuff like building orbital cities or teraforming Mars. 
.1 to .2 will work well enough for near stars. 

0.2 is about the best conceivable without ridiculous energy capture technology eh?

So ~22 years to Alpha/Proxima, ~80 years to Gliese832, ~110 years to Gliese667C

 

ADDIT: so here is my next question that doesn't warrant its own thread: given that the Faraday's work on electromagnetism was 1820s, why was there such a long delay till Roentgen's controlled creation of X-rays (1895), but then very rapid discoveries about nuclear physics in the last decade of the 19th century culminating in Rutherford and Einstein's works ~1900 to 1904? I don't know enough about the details of the experiments physicists and engineers were conducting in the latter half of the 19th century to say with certainty, but it seems to me that there were NOT real technical barriers to the "discoveries" made by Roentgen, Becquerel, the Curies, etc. and which laid the ground work for the theory of atomic energy?

And then another curious delay: 35 years until the first actual controlled nuclear fission reaction by Fermi (1935).

Edited June 14, 2018 by Diche Bach
Elaboration

[kerbiloid]

At least they needed photography (1830s-1840s) to visualise and save the picture,
And a table of chemical elements (1830s-1870s) to identify the source.

Edited June 14, 2018 by kerbiloid

[magnemoe]

4 hours ago, kerbiloid said:

At least they needed photography (1830s-1840s) to visualise and save the picture,
And a table of chemical elements (1830s-1870s) to identify the source.

Radioactivity was discovered pretty much by accident with radium and an photographic plate, not easy to detect radioactivity if you have no idea it exist. Even radio waves was not discovered until end of 19th century. 

First reactor might be that it was a bit larger than an lab experiment. Also that chain reaction was not discovered until the 20's as I remember

[kerbiloid]

2 hours ago, magnemoe said:

Radioactivity was discovered pretty much by accident with radium and an photographic plate, not easy to detect radioactivity if you have no idea it exist.

It's a random process with increasing probabilty.
While the photography was getting more and more popular, probability of a random photoplate lying in a laboratory is rising.
While the chemistry extracts more and more pure elements, probability of a random radioactive piece lying near a random photoplate is rising.
At last somebody somewhere with necessity puts them together and wonders.

So, this seeming radnomness has taken place when historical preconditions had gotten mature.

[Diche Bach]

1 hour ago, kerbiloid said:

It's a random process with increasing probabilty.
While the photography was getting more and more popular, probability of a random photoplate lying in a laboratory is rising.
While the chemistry extracts more and more pure elements, probability of a random radioactive piece lying near a random photoplate is rising.
At last somebody somewhere with necessity puts them together and wonders.

So, this seeming radnomness has taken place when historical preconditions had gotten mature.

Wow . . .

So ~1825-26 Photography: https://en.wikipedia.org/wiki/Photography#Invention_of_photography

Taxonomy of elements: https://en.wikipedia.org/wiki/Periodic_table#History sounds like that was more or less a constant "work in progress" from 1790s through till the 1970s!

There really IS value to thinking outside the box it seems.

Imagine if the prevailing standards of today (negative results are almost never worth publishing) had held true in 1887 and the Michelson-Morley experiments null results had not been published

[YNM]

13 hours ago, Diche Bach said:

And then another curious delay: 35 years until the first actual controlled nuclear fission reaction by Fermi (1935).

Basically, S curves.

But why, I'm not sure.

[Diche Bach]

6 minutes ago, YNM said:

Basically, S curves.

But why, I'm not sure.

Good stuff

Intriguing that Szilard's thinking was 'sparked' by Wells Sci Fi  . . . and that suit though!

[kerbiloid]

17 minutes ago, Diche Bach said:

So ~1825-26 Photography: https://en.wikipedia.org/wiki/Photography#Invention_of_photography

Invention. But how many scientists were also photographers and occasionally put photoplates in their lab?
Say, first guns were invented and used iirc in XIII century. But it took 3 centuries more to make armored knights useless, when muskets were being manufactured inamounts of thousands.
So, not an invention decides, but a common use.

17 minutes ago, Diche Bach said:

Taxonomy of elements: https://en.wikipedia.org/wiki/Periodic_table#History sounds like that was more or less a constant "work in progress" from 1790s through till the 1970s!

But only since 1830s they were creating more or less clear picture of what are elements.
Say, X-ray and visible light were considered as different types of aethereal waves. And early XIX chemists would not understand what is radium.

Edited June 14, 2018 by kerbiloid

[Diche Bach]

2 minutes ago, kerbiloid said:

Invention. But how many scientists were also photographers and occasionally put photoplates in their lab?
Say, first guns were invented and used iirc in XIII century. But it took 3 centuries more to make armored knights useless, when muskets were being manufactured inamounts of thousands.
So, not an invention decides, but a common use.

But only since 1830s they were creating more or less clear picture of what are elements.
Say, X-ray and visible light were considered as different types of aethereal waves. And early XIX chemists would not understand what is radium.

Yep! Good points.

In any event, thanks for the feedback guys!

Watch out Harry Turtledove! Here I come! 

[YNM]

27 minutes ago, kerbiloid said:

Say, first guns were invented and used iirc in XIII century. But it took 3 centuries more to make armored knights useless, when muskets were being manufactured inamounts of thousands.
So, not an invention decides, but a common use.

More than that : It has much more to do with rifling.

 

Edited June 14, 2018 by YNM

[kerbiloid]

1957, operation Plumbbob, test Pascal-B, 0.3 kt yield, that famous steel cap thrown away.

Quote

During the Pascal-B nuclear test, a 900-kilogram (2,000 lb) steel plate cap (a piece of armor plate) was blasted off the top of a test shaft at a speed of more than 66 km/s (41 mi/s; 240,000 km/h; 150,000 mph).

So, the cap kinetic energy = 900 * 66000² / 2 / 4.2*10¹² = 0.47 kt.

Question A.  How could a 0.3 kt explosion provide 0.47 kt of kinetic energy?

Ok, let it be so.
They believe that the cap has been

Quote

vaporized by compression heating of the atmosphere due to its high speed

But the cap has 

Quote

appeared in one frame

So, right after getting out of the ground it was still an object.

So, if it has been vaporized, that happened after the cap has been seen in air.

Question B. Where is aerial explosion of 0.47 kt yield?

[Terwin]

5 hours ago, kerbiloid said:

1957, operation Plumbbob, test Pascal-B, 0.3 kt yield, that famous steel cap thrown away.

So, the cap kinetic energy = 900 * 66000² / 2 / 4.2*10¹² = 0.47 kt.

Question A.  How could a 0.3 kt explosion provide 0.47 kt of kinetic energy?

In addition to the projected nuclear energy, there are often conventional explosives used as part of the trigger mechanism.

As the entire thing was enclosed in a tube with a plug at one end(basically like a giant pop-gun), all of the explosive force(both conventional and nuclear) could easily have worked together to throw the 'cork'

There is also the possibility that 0.3kt is the expected useful yield, and that other components of the reaction that are not generally considered part of the useful yield could have contributed due to the nature of the set-up(vaporization of the container walls due to types of radiation that are not generally considered useful for example) 

5 hours ago, kerbiloid said:

So, right after getting out of the ground it was still an object.

So, if it has been vaporized, that happened after the cap has been seen in air.

Question B. Where is aerial explosion of 0.47 kt yield?

Think more meteor and less ICBM.  As the plate ablates due to friction with the atmosphere, both the encountered air and the ablated particulates would carry away some of that energy.  Even compressing the air above the plate due to the plate moving faster than the air can get out of the way would take a lot of energy and that would mostly result in just reorganizing the air a bit(and probably some sort of sonic boom).

[kerbiloid]

20 minutes ago, Terwin said:

In addition to the projected nuclear energy, there are often conventional explosives used as part of the trigger mechanism.

But unlikely with total yield many times greater than the nuke itself,
That 0.47 kt would just a tiny part of the explosion energy, just because the cap is small compared to the area of the spheric surface at its distance.

Also unlikely they could burst several kilotons instead of expected 0.3 kt.

20 minutes ago, Terwin said:

Think more meteor and less ICBM.  As the plate ablates due to friction with the atmosphere, both the encountered air and the ablated particulates would carry away some of that energy.  Even compressing the air above the plate due to the plate moving faster than the air can get out of the way would take a lot of energy and that would mostly result in just reorganizing the air a bit(and probably some sort of sonic boom).

Yes, but the most part of the air is held in several kilometers above the ground.
Atmospheric scale is ~8 km, so the air is mostly below ~5..7 km altitude or so.

Meteoroids come from above, they first pass the upper, thin layers, getting hotter and hotter.
When they arrive to the lower layers, their heating faster and faster, so they burst in the last several kilometers of the air.

And the cap ascends, it passes first the lowest, the densest layers of the air, which its maximum speed.
The higher it gets, the slower it flies, and the thinner is air.

While the cap is passing first several kilometers, its heating rate should be decreasing fast.
So, it should either vaporize at zero to several kilometers, or should fly away getting cooler and cooler.

Ok, let it be not a fireball. But where is a fire arrow from down to up, with a smoke trace?
Where is another clap of thunder caused by the bolide being vaporized?

Edited June 15, 2018 by kerbiloid

[Terwin]

25 minutes ago, kerbiloid said:

But unlikely with total yield many times greater than the nuke itself,
That 0.47 kt would just a tiny part of the explosion energy, just because the cap is small compared to the area of the spheric surface at its distance.

Also unlikely they could burst several kilotons instead of expected 0.3 kt.

The entire explosion(nuclear+conventional) was constrained by the surrounding rock.  Remember, this was an underground test that took place in a very deep pit, and the only vent for all of that energy was covered by the cap.

Just like the difference between putting a small piece of lead on top of a small pile of gunpowder and shooting a bullet out of a gun.

I don't know where the 'extra' 0.17 kt came from, but there is no need for multiple kt to explain it.

25 minutes ago, kerbiloid said:

Yes, but the most part of the air is held in several kilometers above the ground.
Atmospheric scale is ~8 km, so the air is mostly below ~5..7 km altitude or so.

Meteoroids come from above, they first pass the upper, thin layers, getting hotter and hotter.
When they arrive to the lower layers, their heating faster and faster, so they burst in the last several kilometers of the air.

And the cap ascends, it passes first the lowest, the densest layers of the air, which its maximum speed.
The higher it gets, the slower it flies, and the thinner is air.

While the cap is passing first several kilometers, its heating rate should be decreasing fast.
So, it should either vaporize at zero to several kilometers, or should fly away getting cooler and cooler.

Ok, let it be not a fireball. But where is a fire arrow from down to up, with a smoke trace?
Where is another clap of thunder caused by the bolide being vaporized?

Meteoroids only burst if they have pockets of volitiles inside of them(like ice or gas) and those expand form the heat, causing the rock to burst.

Usually they just disintegrate as parts ablate or get torn off by the atmosphere.

Also very few are as dense, even, or tough as a one ton chunk of armor plating, so it is entirely possible that it managed to leave the dense part of the atmosphere before it had warmed enough for any obvious effect.

I would expect that any 'sonic boom' would have been close enough to be hard to distinguish from the over-pressure wave of the initial explosion.

If the cap did not heat up enough to glow while still in the atmosphere, there would have been no visible 'fire arrow'(even if it did, it probably would not have started glowing until much higher, and with a high speed and a dim glow, there would have been very little to see)  Unless the cap vaporized, there would be no source of smoke, so no smoke trace.

[kerbiloid]

30 minutes ago, Terwin said:

I don't know where the 'extra' 0.17 kt came from, but there is no need for multiple kt to explain it.

Quote

If, say, the cap was lying right on the charge, covering, say, 1/3 of total sphere, the charge should be at least 0.47 * 3 = 1.5 kt.
So, at least 5 times greater than 0.3 kt.

30 minutes ago, Terwin said:

Meteoroids only burst if they have pockets of volitiles inside of them(like ice or gas) and those expand form the heat, causing the rock to burst.

Usually they just disintegrate as parts ablate or get torn off by the atmosphere.

Yes. And the cap should either disintegrate at first several kilometeres (where almost all air is held), or happily fly away, as at ~8 kilometers it has already passed 2/3 of atmosphere, and unlike a rocket, it isn't accelerating, it's decelerating.
 

30 minutes ago, Terwin said:

I would expect that any 'sonic boom' would have been close enough to be hard to distinguish from the over-pressure wave of the initial explosion.

Several km / 66 km/s ~0.1 s.
So, they should have two explosion events separated by 0.1 s.
Also (I've took a look) they usually were using accelerographs (?) with measurement accuracy ~1%.
Yield values of different tests are listed with "12.8 kt +/- 6 t" accuracy level.
So, unless total yield was ~hundreds kt, that 0.47 kt would not get lost, 
(Unfortunately I don't have a report about exactly this test).

And if it were exploded in mid-air, the secondary aerial shockwave would come from above, and the secondary seismic boom would happen and be registered after it.
But nobody mentioned a double boom, nobody mentioned an explosion or flash above the dust cloud.

30 minutes ago, Terwin said:

If the cap did not heat up enough to glow while still in the atmosphere, there would have been no visible 'fire arrow'(even if it did, it probably would not have started glowing until much higher, and with a high speed and a dim glow, there would have been very little to see)  Unless the cap vaporized, there would be no source of smoke, so no smoke trace.

If the cap had exploded realeasing ~0.47 kt of energy, nobody would see a hot cap, but everybody - a sphere or a thin cylinder of heated air.
A nuke fireball is not a glowing bomb, it's a hot air around it.  The same with this cap. 
(Ok, instead of "smoke" I should say "condensating water steam trace").

Edited June 15, 2018 by kerbiloid

[Terwin]

1 hour ago, kerbiloid said:

If, say, the cap was lying right on the charge, covering, say, 1/3 of total sphere, the charge should be at least 0.47 * 3 = 1.5 kt.
So, at least 5 times greater than 0.3 kt.

Except the walls of the chamber containing the nuke test blocked all avenues of escape *EXCEPT* the opening covered by the cap, therefore the cap should have been accelerated by ~100% of the kinetic energy for the blast.

Just like the bullet in a rifle only covers a small portion of the surface-area of the gunpowder but still gets nearly 100% of the energy from the charge. 

1 hour ago, kerbiloid said:

Several km / 66 km/s ~0.1 s.
So, they should have two explosion events separated by 0.1 s.
Also (I've took a look) they usually were using accelerographs (?) with measurement accuracy ~1%.
Yield values of different tests are listed with "12.8 kt +/- 6 t" accuracy level.
So, unless total yield was ~hundreds kt, that 0.47 kt would not get lost, 
(Unfortunately I don't have a report about exactly this test).

If I recall correctly, a sonic boom does not travel backwards, only forwards along the path of the super-sonic entity.  As such, there is no reason for anyone on the ground, only aircraft that happened to be flying in the restricted air-space very close to a nuclear test, and those would all have been shot down before being allowed to get that close.

As such, only the over-pressure from the actual explosion would make an obvious boom for ground observers.

Also, remember that the sound of the explosion is also traveling at the speed of sound(in fact the over-pressure wave that pushed the cap off the hole could reasonably be called the 'sound' of the explosion), as such, even if there was a sonic boom, it would be caused along the surface of, and travel along with, the wave-front of the explosion sound, making them indistinguishable without precise digital analysis comparing two identical explosions, one with the additional 'sonic boom' and one without.

 

If the cap flew up into space, or even if it melted on the way there, there is no compelling reason for it to have been obvious or to have left any obvious evidence behind that would be particularly distinct from the forming mushroom cloud, especially for the relatively primitive recording instruments of the day.

[kerbiloid]

51 minutes ago, Terwin said:

Except the walls of the chamber containing the nuke test blocked all avenues of escape *EXCEPT* the opening covered by the cap, therefore the cap should have been accelerated by ~100% of the kinetic energy for the blast.

Just like the bullet in a rifle only covers a small portion of the surface-area of the gunpowder but still gets nearly 100% of the energy from the charge. 

The cap was just covering the test shaft. So, in any case it could get just a small part of the energy, and in no case 150%.

51 minutes ago, Terwin said:

If I recall correctly, a sonic boom does not travel backwards, only forwards along the path of the super-sonic entity.

This would be not a sonic boom, this would be a spherical shockwave generated by a spherical volume of air suddenly heated with isotropic radiation of the vaporized cap.
Sonic boom energy of 1 t cap is negligible here.
It would be like any other explosion.

So it would hit the ground like a shockwave or an acoustic wave (depending on the explosion altitude), and would be visible for the observers, like a 0.47 kt explosion on top of Everest.
And the higher it bursts, the greater would be this time delay between two explosion events.
So, they would get a clear second peak in 0.1 to 20 seconds, depending on the cap vaporization altitude, and see/film a flash in the sky.

51 minutes ago, Terwin said:

especially for the relatively primitive recording instruments of the day.

Not so primitive, btw, there was a plenty of instruments in tens of points around every test, I should copypaste about twenty pages of their description.
But it doesn't matter, as this was just a set of shockwaves which were being accurately registered decades before.

51 minutes ago, Terwin said:

obvious evidence behind that would be particularly distinct from the forming mushroom cloud

Mushroom cloud gets formed on any more or less significant turbulence in an air full of dust.
Probably, Pascal-B didn't form it at all, as it was underground (can't find a photo of this test).

Edited June 15, 2018 by kerbiloid

[Terwin]

On 6/15/2018 at 1:30 PM, kerbiloid said:

The cap was just covering the test shaft. So, in any case it could get just a small part of the energy, and in no case 150%.

Ok, let's go back to your earlier number of 1/3 of the sphere being covered by the cap(obviously it would be much less as if the explosion was that close, the cap would probably have been vaporized, but for now I'll assume 1/3)

If 1/3 of the energy of the 0.3kt explosion came out of the opening of the test shaft(where it knocked off the cap), where did the other 0.2kt of the explosion go?

All of that expanding plasma/super-heated air had to go somewhere, and I strongly doubt that it was all somehow perfectly absorbed by the walls of the shaft.

 

[kerbiloid]

1 hour ago, Terwin said:

If 1/3 of the energy of the 0.3kt explosion came out of the opening of the test shaft(where it knocked off the cap), where did the other 0.2kt of the explosion go?

It melts the stone and pushes aside the melted material, creating a spherical chamber. The heat dissipates into the rock through the walls.
Above the spherical chamber there appears a cylindrical shaft a little narrower than the chamber, where hot gases are ascending. It may or may not reach the ground surface, depending on depth and yield.
Later the cylindrical shaft and cavern partially or totally collapse, so there can be either a cavern below the ground, or a crater on surface, or both.

[NSEP]

If you approach the speed of light, your mass will increase and you will need more energy to move forward, but doesn't that mean that the mass of the fuel will also increase?

Does that mean that the mass increases but the energy doesn't?

Did i read it wrong?

 

[Tullius]

3 hours ago, NSEP said:

If you approach the speed of light, your mass will increase and you will need more energy to move forward, but doesn't that mean that the mass of the fuel will also increase?

Does that mean that the mass increases but the energy doesn't?

Did i read it wrong?

That happens only if we are speaking of "relativistic mass". E=mc^2 only holds for a mass at rest, for moving masses the formula is E=gamma*mc^2, where gamma = 1/sqrt(1-v^2/c^2), where v is the speed of the object.

The kinetic energy of the object is therefore E=(gamma-1)*mc^2, which in first order approximation leads to the classical formula of kinetic energy E=1/2*mv^2 (This works fine up to about 10% of the speed of light).

[wumpus]

On 6/14/2018 at 5:03 AM, magnemoe said:

Radioactivity was discovered pretty much by accident with radium and an photographic plate, not easy to detect radioactivity if you have no idea it exist. Even radio waves was not discovered until end of 19th century. 

First reactor might be that it was a bit larger than an lab experiment. Also that chain reaction was not discovered until the 20's as I remember

I'm pretty sure that radioactivity was discovered by some other element and a photographic plate,  or perhaps radium long before Curie isolated and named it.  You wouldn't call it radium until you isolated and noticed how bright it is on its own.

[Terwin]

6 hours ago, wumpus said:

I'm pretty sure that radioactivity was discovered by some other element and a photographic plate,  or perhaps radium long before Curie isolated and named it.  You wouldn't call it radium until you isolated and noticed how bright it is on its own.

Curie was a Doctoral student in the lab where it was discovered, she discovered that it was only caused by certain elements and gave it a name.

So before, sure.  Long before?  Not really.

Was probably even the same piece of radium.

[Mad Rocket Scientist]

Can you produce methane from hydrogen and carbon in the form of graphite?

[kerbiloid]

11 hours ago, Mad Rocket Scientist said:

Can you produce methane from hydrogen and carbon in the form of graphite?

They say:

• C _(coke) + 2 H₂ → _{Pt, 600°C} → CH₄
• C _(graphite)  + 2 H₂ → _{Ni, 600-1000°C} → CH₄
• 2 C _(coke) + H₂ → _1500-2000°C → C₂H_{2 (acetylene)}