For Questions That Don't Merit Their Own Thread

[kerbiloid]

Wi-fi missiles. They don't need physical lines to connect to the tank.

[JoeSchmuckatelli]

59 minutes ago, kerbiloid said:

Wi-fi missiles. They don't need physical lines to connect to the tank.

People will still complain of bad connection

[JoeSchmuckatelli]

Question for the smart guys: how does something so diffuse as the gasses between galaxies have temperatures in the millions of degrees?

Quote

The Chandra data shows gas in the merging clusters with temperatures of millions of degrees. The optical data shows galaxies in the clusters and other, more distant, galaxies lying behind the clusters. Some of these background galaxies are highly distorted because of gravitational lensing, the bending of light by massive objects. This effect can also magnify the light from these objects, enabling astronomers to study background galaxies that would otherwise be too faint to detect. Finally, the structures in the radio data trace enormous shock waves and turbulence. The shocks are similar to sonic booms, generated by the mergers of the clusters.

 

Chandra :: Photo Album :: Frontier Fields Galaxy Clusters :: March 10, 2016 (harvard.edu)

@K^2 - you still here?

Edited November 21, 2022 by JoeSchmuckatelli

[Kerwood Floyd]

I am far from a smart guy (I get the feeling you're smarter than I am) but . . .

I think the secret is that temperature and heat are not exactly the same thing. I remember once reading a similar discussion wherein a smart guy pointed out that, while the average temperature of North Atlantic water is not much above freezing, it still contains a tremendous amount of heat energy. In a similar way, I think those interstellar clouds of gas contain very little heat energy while having a high temperature.

[sevenperforce]

On 11/21/2022 at 10:26 AM, JoeSchmuckatelli said:

Question for the smart guys: how does something so diffuse as the gasses between galaxies have temperatures in the millions of degrees?

 

Chandra :: Photo Album :: Frontier Fields Galaxy Clusters :: March 10, 2016 (harvard.edu)

Well, temperature and pressure are funny things. The temperature of a gas is really just a way of measuring the average kinetic energies of the molecules in the gas, and pressure is simply the average impulse per unit time produced by molecular collisions against a given internal area. Let's suppose the temperature in your room is 25°C. The individual air molecules you're breathing in and out right now are zipping around the room at around 500 m/s . . . some a little faster, some a little slower. For an average adult male, you're experiencing about 3.68e27 of these collisions every second. You feel these collisions and their kinetic energy as a combination of pressure and temperature.

We could, however, increase the temperature in the room while decreasing the pressure. When we do that, you'll have fewer collisions (so you feel less pressure), but each collision will deposit more thermal energy in you. Because there will be fewer collisions, you'll gain heat much more slowly, but you'll definitely feel yourself getting hotter.

Eventually, the oxygen partial pressure would be too low for you to maintain blood oxygenation, and you'd suffocate (and roast) simultaneously. Not fun.

If I have a box of gas with an internal heat source (let's say a thermostatic electrical resistance heater) and I begin to add thermal energy to it, those molecules gain kinetic energy and begin zipping around the inside of the box faster and faster. As long as that box remains closed, the molecules will pick up more and more speed as I add more and more energy to the box. As those molecules bounce around the inside of the box, inelastic collisions with the box transfer some of their kinetic energy to thermal energy in increasing the temperature of the box. Eventually, the temperature of the outside of the box will reach the same temperature as the resistance heater, and the system will be in equilibrium.*

Note that this process is independent of the AMOUNT of gas inside the box. It will still work whether I only have 1 milligram of air molecules inside the box (about 2e19 physical molecules) or if I've pumped 10 grams of air molecules inside the box (2e22 physical molecules). However, it won't work at the same rate. If there are more air molecules, there will be more frequent collisions, and so the thermal energy will propagate much faster. 

But you can see here, again, that temperature is independent of pressure. The box with just 1 milligram of air molecules may have the exact same temperature (average molecular kinetic energy) as the box with 10 grams of air molecules, but the latter box will have a much higher internal pressure (because, again, pressure is simply the average impulse per unit time produced on a given internal area of the container, and there are 1000 times as many air molecules in the latter box, resulting in 1000 times as much pressure).

What happens if we open those boxes? Well, assuming that the temperature inside both boxes is much higher than the temperature of the surroundings, that means the velocity of the air molecules is much higher inside. Those air molecules will all immediately zip off in every direction and be replaced by the slower-moving air molecules in the room. Granted, those high-speed air molecules will still be in the room, at least until they bounce into other air molecules a couple billion times and lose speed, but because the temperature within a gas is based on the average molecular kinetic energy within a volume, the actual temperature of the room will only increase slightly.

The gases between galaxies in dense galaxy clusters are very diffuse, but the molecules are moving extremely fast: on the order of 200 km/s or even higher. And while there's not much for them to bump into, everything else they're bumping into is ALSO moving at 200 km/s or higher, so it's not like they slow down. The gas cloud may be very diffuse, but it's still very, very hot. And inside a gravity cluster, local gravity keeps it from escaping, so. . .there you go.

 

 

_{*Of course, it's not actually in equilibrium, because the box in turn will lose thermal energy to its surroundings. Even if the box is thermodynamically isolated from its surroundings, it will lose energy to blackbody radiation. But we're ignoring that for the time being.}

 

[sevenperforce]

On 11/21/2022 at 11:19 AM, Kerwood Floyd said:

I remember once reading a similar discussion wherein a smart guy pointed out that, while the average temperature of North Atlantic water is not much above freezing, it still contains a tremendous amount of heat energy. In a similar way, I think those interstellar clouds of gas contain very little heat energy while having a high temperature.

So in a sense you're correct, but probably not for the reason you're thinking. The North Atlantic is not much above freezing, but a difference of even one degree spread through 146 cubic kilometers of ocean water is 1.46e17 joules: almost as much as the blast yield of the Tsar Bomba hydrogen bomb. So that's not quite right.

Intergalactic gas clouds in a galaxy cluster are at an extraordinarily high temperature. They also contain an extraordinary amount of heat energy. However, that energy is not concentrated because the clouds are very diffuse; 1 cubic meter of space may only contain about 1000 particles. A cubic meter of air at the surface of Earth contains 2.46e25 particles. So the heat energy per unit volume is low, but the temperature is extremely high and the total heat energy is extremely high.

Note that just because the density is very low does not mean that the "pressure" is low. Because of their high molecular velocity, the intergalactic gas clouds in a galaxy cluster exert quite a bit of pressure on anything they hit. Not much by everyday standards here on Earth, but still significant. 

[JoeSchmuckatelli]

@sevenperforce - thanks very much!

It's Interesting... I figured that being diffuse the gasses would very rapidly lose energy and cool to something similar to the background temperature of the vacuum... Of course I assumed that without thinking about the how.  Thinking about the pressure being more closely related to rate of heating /cooling did not come into my guesswork. 

If I understand you correctly, the particles of gas in the box gain energy from either direct contact with the element or the thermal / infrared radiation given off by it.  Similarly, the gas particles constrained by gravity must be either hot from the emission sources (whatever star they were ejected from) or through absorbing thermal radiation from the stars of the galaxies in the cluster - which keeps them hot. 

So in order to cool, the hot gas particles would have to either hit something else that is cooler (moving towards equalibrium) or cease receiving energy and be able to cool via emissions of their own thermal radiation.  (How'm I doin?) 

Thus because they are constrained by gravity in the region of a cluster, the particles are constantly receiving thermal energy radiation and stay hot. 

Further guessing that whether a ship flying through that region would have to concern itself with the million degrees temperatures melting it would entirely depend on the speed of the craft (which directly affects the rate of collision with the hot particles). 

Cool! 

 

Thanks for your time! 

[sevenperforce]

3 minutes ago, JoeSchmuckatelli said:

I figured that being diffuse the gasses would very rapidly lose energy and cool to something similar to the background temperature of the vacuum... Of course I assumed that without thinking about the how.  Thinking about the pressure being more closely related to rate of heating /cooling did not come into my guesswork. 

An object will only lose energy via cooling if it can transfer its thermal energy to something cooler than itself. It can transfer thermal energy kinetically, through elastic collisions, or it can do so electromagnetically through blackbody radiation.

For intergalactic gases in a dense galaxy cluster, the gas cloud is doing both of these things. The reason we can see the gas clouds at all with the Chandra x-ray telescope is that the gas clouds are so hot that they're radiating in the x-ray spectrum. We are quite literally the electromagnetic heat sink for distant galaxies.

If you had a dense hot gas cloud in otherwise-empty space, then the gas cloud would expand. If it was heavy enough to have meaningful self-gravitation, this expansion would also cool it, because the kinetic energy of its particles would be converted into gravitational potential energy.* But the gas between galaxies can't expand because it doesn't have anywhere to go; it is being squeezed together by the incredible inertia of multiple galaxies.

_{*Counter-intuitively, expansion does NOT produce cooling unless the expansion performs some work. That work can be pushing a piston, displacing the gases in a lower-pressure environment, expanding through a de Laval nozzle to produce thrust, or in the case of a giant gas cloud, converting kinetic energy into gravitational potential energy. On the other hand, if I was to spacewalk outside of the ISS and pop a balloon filled with high-temperature, high-pressure gas, all those gas molecules would fly off in every direction with the same average velocity and thus maintain their "temperature" indefinitely (although they would of course rapidly be lost among all the other diffuse molecules in outer space).  On the other hand, compression does always cause heating, because you cannot compress a gas without applying a force to it and thus performing work, which adds energy.}

16 minutes ago, JoeSchmuckatelli said:

If I understand you correctly, the particles of gas in the box gain energy from either direct contact with the element or the thermal / infrared radiation given off by it.  Similarly, the gas particles constrained by gravity must be either hot from the emission sources (whatever star they were ejected from) or through absorbing thermal radiation from the stars of the galaxies in the cluster - which keeps them hot.

Well, what's heating up the gas particles in this instance is the fact that they are being compressed by the inertia of the galaxies that are being dragged together by gravity.

There are four different galaxy clusters (or subclusters) presently colliding with each other in this image. Subcluster B is smashing into subclusters A, C, and D at a speed of approximately 3,000 kilometers per second. That is the incredible pressure which squoze (as far as I'm concerned, that's the technical term) the gas between the galaxies to a temperature of 90 millionºC.

Thus the gas clouds in the cluster are much hotter and thus much greater emitters of light than the stars around them.

19 minutes ago, JoeSchmuckatelli said:

in order to cool, the hot gas particles would have to . . . cease receiving energy and be able to cool via emissions of their own thermal radiation.

Here's where it gets a little complicated. Individual molecules can't "cool"  by thermal radiation; their temperature is simply their velocity, and all velocities are relative, so they have no way of knowing how "fast" they are going in the first place. In addition, because energy is quantized, they wouldn't be able to "cool" gradually at all; atoms and molecules can only emit or absorb specific lights within specific wavelengths corresponding to their energy states.

Thermal radiation, more properly known as blackbody radiation, occurs on the order of macroscopic objects comprising many particles such that there are many many energy levels and atomic transitions and so the radiation they emit follows a certain distribution. The gas cloud as a whole is of course emitting a bunch of blackbody radiation, as noted above, but that blackbody radiation is a distribution of photons produced by innumerable collisions between individual gas molecules and atoms.

It should be noted that in this sort of a situation, there are no molecules to speak of. The temperature is far, far too high for covalent bonds; it's all a diffuse plasma. At lower temperatures, blackbody radiation can be produced by atomic transitions; two atoms smack into each other, raising the energy state of the electrons in both atoms, and as those electrons collapse back to their lowest energy, they release photons in frequencies corresponding to those different energy states. However, in this sort of extreme situation, the distribution of photons is dominated by the Bremsstrahlung process, where a charged particle moving at high speed loses energy and releases a photon when it passes through an electric field.  The dominant luminous component in a galaxy cluster is thermal bremsstrahlung. 

No matter how fast it is going, a particle cannot produce bremmstrahlung radiation by itself. It has to interact with another particle.

36 minutes ago, JoeSchmuckatelli said:

guessing that whether a ship flying through that region would have to concern itself with the million degrees temperatures melting it would entirely depend on the speed of the craft

Considering that this region is producing thermal x-rays visible at a distance of 5.4 billion light years, the "temperature" of the cloud is not going to be the primary problem for your hypothetical spacecraft.

The thermal radiation transferred to the spaceship would melt it six times faster than if it was at the center of the sun.

[JoeSchmuckatelli]

1 hour ago, sevenperforce said:

The thermal radiation transferred to the spaceship would melt it six times faster than if it was at the center of the sun.

Laughing *literally* out loud!

I'm learning a lot from what you've written.  Thinking of a gas cloud as a 'body' and that the emissions we're reading from them are blackbody just flipped my brain a little bit.  (Can we even call it properly a 'gas' cloud?  Plasma cloud?)   If pressed I would have said we were seeing reflected emissions from the conglomeration of stars and BHs within the galaxies.

I'd also breezed past what Chandra was telling us - of course it's x-ray, and thus highly energetic.  Intergalactic space now seems a lot more dangerous than I'd given it credit for!

1 hour ago, sevenperforce said:

The reason we can see the gas clouds at all with the Chandra x-ray telescope is that the gas clouds are so hot that they're radiating in the x-ray spectrum...

Considering that this region is producing thermal x-rays visible at a distance of 5.4 billion light years, the "temperature" of the cloud is not going to be the primary problem for your hypothetical spacecraft.

We are quite literally the electromagnetic heat sink for distant galaxies.

eep!

1 hour ago, sevenperforce said:

Here's where it gets a little complicated. Individual molecules can't "cool"  by thermal radiation; their temperature is simply their velocity, and all velocities are relative, so they have no way of knowing how "fast" they are going in the first place. In addition, because energy is quantized, they wouldn't be able to "cool" gradually at all; atoms and molecules can only emit or absorb specific lights within specific wavelengths corresponding to their energy states.

This part I'm gonna have to wrestle with a bit.  Because what you're describing is a lot like what I've thought I understood about light.  You use the word molecule above - and I figured a hydrogen atom in a gas (skipping over the plasma part for now) would behave a lot more like regular matter than something like a photon.  Just as a rock can have a temperature, I figured the constituent atoms would have a fraction of that... but now as I type this I'm remembering the phrase 'excited state' which I guess can be read as 'velocity'.

So if I have a hot gas in a balloon, I'm guessing the temperature isn't measured in the atom itself, but rather by its velocity which is reflected by the hot gas expanding the balloon more than the same amount of cool gas - by kinetic force?  Thinking of the temperature of the gas as not something that is a combination of all of the individual molecule's temperature writ large, but rather as a function of the combined molecular velocity? [Mind blown emoji]

 

 

 

Here's an unrelated question:  If a mix of gasses ejected from stars gets heated up to the point it all phases into a plasma... if that plasma cools, does it phase back into the original atoms?  

So when a star goes SN and creates a cloud of dust and gasses - if that cloud gets heated to such extremes that it phase changes into a plasma... how is the information retained of what it started as?  Can you say 'hydrogen plasma' and 'oxygen plasma' in any meaningful sense... or is plasma just plasma?

Edited November 22, 2022 by JoeSchmuckatelli

[Terwin]

16 hours ago, JoeSchmuckatelli said:

Here's an unrelated question:  If a mix of gasses ejected from stars gets heated up to the point it all phases into a plasma... if that plasma cools, does it phase back into the original atoms?  

So when a star goes SN and creates a cloud of dust and gasses - if that cloud gets heated to such extremes that it phase changes into a plasma... how is the information retained of what it started as?  Can you say 'hydrogen plasma' and 'oxygen plasma' in any meaningful sense... or is plasma just plasma?

Plasma is when electrons and nuclei are disassociated, so while you can easily have an oxygen nucleus flying around without electrons, or a hydrogen nucleus flying around without an electron(ie a proton), you could not, for example, have a water nucleus flying around without electrons, as the atoms are held together by the electron interactions, and there are no electrons to hold them together.

On the other hand, if I remember correctly, electrons are identical, so once the atoms regain the appropriate number of electrons, they are indistinguishable from their pre-plasma state(unless you ionized a more complex molecule, in which case the nuclei could easily swap around and end up paring with different nuclei when 'cool')

[kerbiloid]

Electrons! You are ightweight! Your are sqrt(940/0.5) ~= forty times faster than those bulky ions!

Escape and be free! Let them ions be a dull cloud of pure positiveness.

[sevenperforce]

18 hours ago, JoeSchmuckatelli said:

20 hours ago, sevenperforce said:

Here's where it gets a little complicated. Individual molecules can't "cool"  by thermal radiation; their temperature is simply their velocity, and all velocities are relative, so they have no way of knowing how "fast" they are going in the first place. In addition, because energy is quantized, they wouldn't be able to "cool" gradually at all; atoms and molecules can only emit or absorb specific lights within specific wavelengths corresponding to their energy states.

This part I'm gonna have to wrestle with a bit.  Because what you're describing is a lot like what I've thought I understood about light.  You use the word molecule above - and I figured a hydrogen atom in a gas (skipping over the plasma part for now) would behave a lot more like regular matter than something like a photon.  Just as a rock can have a temperature, I figured the constituent atoms would have a fraction of that... 

Well, for one thing, it's correct to think of individual atoms behaving more like photons than like clumps of matter. That's particle-wave duality for you.

It might seem counter-intuitive, but individual atoms zipping around freely in a gas can't have a "temperature" at all. They're just particles with some velocity relative to their surroundings. You can think of it in terms of information, if you want: if an atom could have a "temperature" then where would the information about its temperature be stored? It's literally just an atom.

18 hours ago, JoeSchmuckatelli said:

now as I type this I'm remembering the phrase 'excited state' which I guess can be read as 'velocity'.

That's not quite right. An atom's kinetic energy comes from its velocity, which of course is relative to its surroundings. However, energy stored in an excitation state is intrinsic to the atom. The electrons of an atom have orbitals, discrete locations relative to the nucleus at which they can be located. When an atom absorbs energy (either from absorbing a photon of light or from an electromagnetic interaction with another atom during a collision), that "pushes" the electron up into a higher orbital. The electron will then "fall" back down to the ground-state orbit, releasing a photon with energy equivalent to the difference in potential energies between the two orbitals.

A single hydrogen atom with a single electron has 6 different orbitals (n₁ to n₆). When the electron "falls" to n₁ from n₂, n₃, or n₄, it releases an ultraviolet photon, when it falls to n₂ from n₃, n₄, n₅, or n₆ it releases a visible-light photon, and when it falls to n₃ from n₄, n₅, or n₆ it releases an infrared photon:

So an atom can store potential energy in excited states, and it can release that energy in the form of photons, but that's distinct from concepts of "temperature" which depend only on relative velocity.

18 hours ago, JoeSchmuckatelli said:

Thinking of the temperature of the gas as not something that is a combination of all of the individual molecule's temperature writ large, but rather as a function of the combined molecular velocity? [Mind blown emoji]

Exactly right.

18 hours ago, JoeSchmuckatelli said:

If a mix of gasses ejected from stars gets heated up to the point it all phases into a plasma... if that plasma cools, does it phase back into the original atoms?  

So when a star goes SN and creates a cloud of dust and gasses - if that cloud gets heated to such extremes that it phase changes into a plasma... how is the information retained of what it started as?  Can you say 'hydrogen plasma' and 'oxygen plasma' in any meaningful sense... or is plasma just plasma?

Plasma isn't not-atoms. An oxygen plasma is made of oxygen atoms, a hydrogen plasma is made of hydrogen atoms, and a nitrogen plasma is made of nitrogen atoms. Plasma is still very much composed of atoms, they are just atoms which are missing one or more electrons.

Remember hydrogen, up above? I showed what happens when you add energy to an atom up to the n₆ orbital. However, if you give that electron enough energy, it will eventually break free of the atomic nucleus altogether, zipping off as a free electron. However, the static electrical charge of the electron and the atomic nucleus want to pull them back together, and so this new state of matter remains electrostatically neutral. Plasma is a state of matter in which at least some of the electrons which would normally be bound to their atomic nuclei have so much energy that they are bouncing around freely between atoms.

There's one other issue, though: to be a plasma, you don't have to have complete electron disassociation. An oxygen atom may only lose a single atom and it would still be part of a plasma. And while @Terwin is correct that you couldn't have a "water plasma" because you would first need to break the covalent electron-bonds before stripping off any electrons, that's not true of all molecules. Diatomic nitrogen's triple bond is extremely strong, and so you can absolutely have a N*₂ ion in which the covalent bonds remain but a valence electron has been stripped away.

It should be noted that in a plasma-gas cloud that is 90 million degrees, you're going to have complete disassociation.

3 hours ago, Terwin said:

if I remember correctly, electrons are identical, so once the atoms regain the appropriate number of electrons, they are indistinguishable from their pre-plasma state

Yep! All electrons are identical, so there's no difference if they get swapped around from atom to atom.

[Rutabaga22]

What is this on Perseverance? 

[sevenperforce]

1 hour ago, Rutabaga22 said:

What is this on Perseverance? 

That is the X-band high-gain steerable antenna used for most downlinks to transmit data back to Earth.

[Rutabaga22]

Why is metallic hydrogen metastable? What does metastable even mean?

[Gargamel]

#puts on riot helmet and draws sword#
 

Ok you may proceed to answer that question. 

[kerbiloid]

5 hours ago, Rutabaga22 said:

Why is metallic hydrogen metastable?

It isn't.

5 hours ago, Rutabaga22 said:

What does metastable even mean?

You put a look on it, and it disappears under its weight.

(Saying "boo!" makes same effect.)

P.S.
Historically in late XX it was  a hope that if compress some amount of cold hydrogen very-very much under enormous-enormous pressure, a piece of it will stay metallic (and thus dense) even under just-enormous pressure.

This would allow to use such hydrogen icicle as an effective particle source to induce more effective fission or even pure fusion reactions, to use it in weapons or maybe later even in nuclear reactors engines.

But no further successful studies are known. Either because the idea failed, or vice versa because it succeeded so much that those who know better are either silent, or ever-silent.

[DDE]

6 hours ago, Rutabaga22 said:

Why is metallic hydrogen metastable? What does metastable even mean?

With regards to metallic hydrogen, that's more of a wish and a possibility.

Metastability means the existence of an equilibrium point alternative to the system's ground state, so the system can retain potentially useful energy without extern containment. It liberates said energy once knocked out of that states. Ball rolls downhill. Wood burns. Bombs explode.

Spoiler

 

[K^2]

On 11/21/2022 at 7:26 AM, JoeSchmuckatelli said:

how does something so diffuse as the gasses between galaxies have temperatures in the millions of degrees?

It's actually easier at low pressures. I know it sounds unintuitive, but there are two ways a gas molecule (atom, ion...) can lose thermal energy. It either emits a photon or it bumps into something. If the density is low enough, the collisions are going to be very rare. So we're looking primarily at losses to radiation, and the thing to keep in mind is that at frequencies where emission is high, so is absorption. If a photon is likely to be emitted, it's likely to be absorbed again, meaning the energy didn't leave the cloud. So despite potentially being fairly transparent in some wavelengths, the cloud has to be fairly opaque in wavelengths where it can lose energy to radiation, and so it's mostly going to be radiating from the surface. This is where the square-cube principle comes in, and it's a LOT of volume that has to lose heat from just the surface. So it shouldn't surprise you that it takes a very long time for any trapped heat to exit.

Vacuum is a great insulator, after all. We tend to think of that as a feature of something like a thermos bottle, but it's effectively the same principle for a giant cloud of gas in space, except stretched to interstellar distances.

[JoeSchmuckatelli]

9 hours ago, K^2 said:

It's actually easier at low pressures. I know it sounds unintuitive, but there are two ways a gas molecule (atom, ion...) can lose thermal energy. It either emits a photon or it bumps into something. If the density is low enough, the collisions are going to be very rare. So we're looking primarily at losses to radiation, and the thing to keep in mind is that at frequencies where emission is high, so is absorption. If a photon is likely to be emitted, it's likely to be absorbed again, meaning the energy didn't leave the cloud. So despite potentially being fairly transparent in some wavelengths, the cloud has to be fairly opaque in wavelengths where it can lose energy to radiation, and so it's mostly going to be radiating from the surface. This is where the square-cube principle comes in, and it's a LOT of volume that has to lose heat from just the surface. So it shouldn't surprise you that it takes a very long time for any trapped heat to exit.

Vacuum is a great insulator, after all. We tend to think of that as a feature of something like a thermos bottle, but it's effectively the same principle for a giant cloud of gas in space, except stretched to interstellar distances.

This has been a lot more informative of a Q&A than I anticipated.  Always think of the 'vacuum of space' as bitterly cold.  I also figured that we could see the nebular clouds/interstellar dust (what have you), either as backlit shadows, dust lit from within by new stars or reflected light... only. 

It did not dawn on me to consider that they could be so hot.  To the extent that I would have recognized a temperature difference, I'd have gone back to my knowledge of IR and FLIR systems; where what you can see is a temperature differential.  I can see a nebular cloud being warmer than the background of space... but by that amount?  Very eye opening.

[Gargamel]

Is there a term for a word, that when reversed, spells another word?  
 

ie Time & Emit. 

[SunlitZelkova]

59 minutes ago, Gargamel said:

Is there a term for a word, that when reversed, spells another word?  
 

ie Time & Emit. 

Emordnilap/semordnilap.

I’m not even kidding https://savvy-writer.com/words-spelled-backwards-to-form-other-words/

[kerbiloid]

3 hours ago, Gargamel said:

Is there a term for a word, that when reversed, spells another word?  
 

ie Time & Emit. 

https://en.wikipedia.org/wiki/Anadrome

[SunlitZelkova]

How dependent was the development of spaceflight on German research?

I assume Von Braun and Co. themselves weren’t really necessary because Atlas the ICBM was developed without them.

I ask as I am writing an alternate history where the US does not participate directly in WWII, and thus all of Germany comes under Soviet control as the war ends with the capture of a redoubt in western Germany rather than Berlin. That’s not to say the Soviets get Von Braun instead- he might still escape to France and his documents were well hidden- but none of the western Allies are getting his documents either.

So how would that affect postwar US rocket development?

[JoeSchmuckatelli]

3 hours ago, SunlitZelkova said:

How dependent was the development of spaceflight on German research?

I assume Von Braun and Co. themselves weren’t really necessary because Atlas the ICBM was developed without them.

I ask as I am writing an alternate history where the US does not participate directly in WWII, and thus all of Germany comes under Soviet control as the war ends with the capture of a redoubt in western Germany rather than Berlin. That’s not to say the Soviets get Von Braun instead- he might still escape to France and his documents were well hidden- but none of the western Allies are getting his documents either.

So how would that affect postwar US rocket development?

I don't have the sources - but I've heard we were very dependent upon the people: resident knowledge is powerful.  There are TONS of little 'tricks of the trade' that never get written down.

That said - when you know that something is possible, or you have a very good spy network you can figure stuff out or steal the know-how.

There is a present-day analog you might use to guide you.

Edited November 26, 2022 by JoeSchmuckatelli