For Questions That Don't Merit Their Own Thread

[K^2]

5 hours ago, JoeSchmuckatelli said:

how feasible would it be to take the idea of the rotating restaurant and build a facility on earth ...

I know we've been stuck for almost half a century without a superheavy, and that kind of warped our perception of what we can reasonably construct in space, but with SN20 scheduled to take flight this year, giving us ability to put 100+ T to LEO in one go, which is a quarter of the entire ISS mass, should we start talking about at least a tethered centrifuge station?

It seems like a silly waste of time to even experiment with trying to acclimate astronauts on Earth when 500m of cable solves the problem pretty much completely in orbit.

[kerbiloid]

https://www.aalto.fi/en/news/a-new-form-of-carbon

A new form of carbon is discovered, a monoatomic-thin film with metallic properties.

We can start dreaming about inflatable portable spaceships.

[JoeSchmuckatelli]

5 hours ago, K^2 said:

tethered centrifuge station

?? 

I'm not one to quibble with you about anything orbital mechanics related - but if ISS has to reposition, wouldn't being tied to a giant spinning counterweight be a bad idea? 

That said, sure - it would be great to see the potential of SS and heavy lift realized! 

[kerbiloid]

First try to dock there. Then you may start worrying about the orbit raising.

[JoeSchmuckatelli]

Question(s) about photons and light:

I presume that when I heat an element in a dark space, the process by which I see the glowing metal requires the liberation of, or creation of a photon from the element.  Is this correct?

If so... when the light from the element reflects off a nearby surface, allowing me to see that object - am I seeing a photon (the same photon) liberated from the original blackbody emitter - or am I seeing a new photon excited from and/or originating from the object illuminated by the element? 

• (I'm fairly sure that what I'm seeing is a photon from the emitter scattering off the reflective surface).  Similarly, when viewing a translucent object (like a plastic bottle, skin or alabaster) I presume we are seeing photons scattering and reflecting off of different layers of the material that gives it the translucence / semi-transparency we see.  Is this correct?

When I see a shadow of an object - am I correct to assume that the opaque object has sufficient density to scatter the observed wavelength to such a degree that photons from the emitter just cannot penetrate?  i.e. when I shine a flashlight at my hand, I see the shadow of my hand on a plate, but if I send a more energetic particle, like an x-ray, my hand goes from mostly opaque to semi-transparent given the different energies of the observed particles/wavelengths?

When I feel heat from the emitter - I again presume that heat is reaching me via photons  - and the energy from those photons are being absorbed by my skin cells, which are then excited enough to have their temperature raised.  Is this correct?

Finally, If I'm correct thus far in my understanding, can someone help me understand this? - an article that suggests the light we see from a star may be millions of years old before it ever leaves the star and enables us to see it: A Photon’s Million-Year Journey From the Center of the Sun (futurism.com)

I would presume from what I've written above that a photon created in the heart of a star would have been absorbed or scattered to such a degree that what light we are actually seeing from the star is not photons originating in the core, but, effectively, blackbody emissions from the surface, or particles energetic enough that the surface is effectively transparent to them - but originating fairly close to the surface.  (just as the element in a lightbulb creates the photon, but the glass of the bulb is transparent enough for the photons to escape)

The article suggests I have a flaw in my understanding - I just can't get past the photon originating in the core of a star not being absorbed by some atomic interaction in the depth and density of the core that would result in any given photon never being able to escape the core - but one liberated / created closer to the surface could.

 

Edited May 21, 2021 by JoeSchmuckatelli

[kerbiloid]

So, the plastic bags are lovely and healthy again?

https://news.wsu.edu/2021/05/17/new-technology-converts-waste-plastics-jet-fuel-hour/

[AHHans]

6 hours ago, JoeSchmuckatelli said:

I presume that when I heat an element in a dark space, the process by which I see the glowing metal requires the liberation of, or creation of a photon from the element.  Is this correct?

Creating photons is easy! Just tell an electron to take a turn. And in a hot (> 0K) body you have lots of electrons that keep bumping into each other and thus forcing each other to take turns, that's where all your photons come from.

6 hours ago, JoeSchmuckatelli said:

If so... when the light from the element reflects off a nearby surface, allowing me to see that object - am I seeing a photon (the same photon) liberated from the original blackbody emitter - or am I seeing a new photon excited from and/or originating from the object illuminated by the element? 

Well, can you tell the difference between two photons if both have the same quantum state? In other words does it matter if it is the "same" photon if you can't tell the difference?

But IIRC you usually consider photons to be absorbed and then re-emitted when they scatter off a bunch of electrons.

6 hours ago, JoeSchmuckatelli said:

I would presume from what I've written above that a photon created in the heart of a star would have been absorbed or scattered to such a degree that what light we are actually seeing from the star is not photons originating in the core, but, effectively, blackbody emissions from the surface, or particles energetic enough that the surface is effectively transparent to them - but originating fairly close to the surface.  (just as the element in a lightbulb creates the photon, but the glass of the bulb is transparent enough for the photons to escape)

You are correct! The photons we see from the sun are emitted from the outer layers - the so-called photosphere - of the sun. The energy that led to the creation of the photon took quite some time to travel from the core of the sun - where the actual fusion happens - to the outer layers where the created photons can finally escape this ball of plasma and go all the way to Earth.

So the title of that article and its storytelling is mostly poetic license and not literal truth. IMHO this becomes rather obvious when it discusses the convection zone in which the energy is transferred in the form of convection and not by radiation.

[Edit: that was supposed to be another post, but the forum software had other ideas...]

12 minutes ago, kerbiloid said:

So, the plastic bags are lovely and healthy again?

Only if you make sure that all plastic bags are actually collected and recycled!
Oh, and you have a nice and clean way to generate the energy need for collection, transport, and recycling. But let's tackle the problem of making sure that none of the plastic winds up in the ocean first.

Edited May 21, 2021 by AHHans

[K^2]

8 hours ago, JoeSchmuckatelli said:

I'm not one to quibble with you about anything orbital mechanics related - but if ISS has to reposition, wouldn't being tied to a giant spinning counterweight be a bad idea? 

I wouldn't bother repositioning ISS. With this lift capacity, we can build a station whose habitable section is actually designed for 1G. Not to mention that you need the hub, the counterweight... This ought to be a new construction. And probably in much higher orbit to reduce tidal effects.

6 hours ago, JoeSchmuckatelli said:

I presume that when I heat an element in a dark space, the process by which I see the glowing metal requires the liberation of, or creation of a photon from the element.  Is this correct?

Yeah. Black-body radiation page has a bit more info.

6 hours ago, JoeSchmuckatelli said:

If so... when the light from the element reflects off a nearby surface, allowing me to see that object - am I seeing a photon (the same photon) liberated from the original blackbody emitter - or am I seeing a new photon excited from and/or originating from the object illuminated by the element?

Ooof. So I can probably dig into a bit more if you want, but the very short version is that all particles are identical. It is fundamentally impossible to tell between a particle moving and a particle being destroyed and new one created in the new location. In fact, the later is how we describe propagation of particles in QM. So this gets very philosophical very fast. I can claim that "they are all the same photon," as particles are indistinguishable. But I can just as easily claim that a photon only exists for an instance in time and no other photon is the same photon, because no photon at any other instance of time shares that same state (which includes time).

6 hours ago, JoeSchmuckatelli said:

When I see a shadow of an object - am I correct to assume that the opaque object has sufficient density to scatter the observed wavelength to such a degree that photons from the emitter just cannot penetrate?  i.e. when I shine a flashlight at my hand, I see the shadow of my hand on a plate, but if I send a more energetic particle, like an x-ray, my hand goes from mostly opaque to semi-transparent given the different energies of the observed particles/wavelengths?

Scatter, absorb, or both. It's not just about density, though. Water has almost the same density, but will cast only a very faint shadow, while there are plenty of gases opaque enough to absorb light. Interaction between light and matter can get fairly involved.

6 hours ago, JoeSchmuckatelli said:

When I feel heat from the emitter - I again presume that heat is reaching me via photons  - and the energy from those photons are being absorbed by my skin cells, which are then excited enough to have their temperature raised.  Is this correct?

Yeah, that's how radiative heat works. Of course, there can also be convection - if you hold your hand over a hot object, hot air rising from it might be heating your hand directly. Unless you're in a vacuum, it's almost always some combination of radiative heating and heat transfer from environment.

6 hours ago, JoeSchmuckatelli said:

Finally, If I'm correct thus far in my understanding, can someone help me understand this? - an article that suggests the light we see from a star may be millions of years old before it ever leaves the star and enables us to see it

this is just about the time it takes for energy to propagate out of the star's core. There are a whole bunch of state changes along the way, and this eventually leads to emission of light in photosphere via black-body radiation as described in an earlier link. It sounds like your understanding of the process is essentially correct and the article is just poorly written.

Edit: Ninja'd by @AHHans  I could have written a much shorter post. 

Edited May 21, 2021 by K^2

[JoeSchmuckatelli]

1 hour ago, K^2 said:

Ninja'd by @AHHans  I could have written a much shorter post. 

Edited 1 hou

Okay - but you both wrote (effectively) 

 

1 hour ago, AHHans said:

Well, can you tell the difference between two photons if both have the same quantum state? In other words does it matter if it is the "same" photon if you can't tell the difference

Which is one of those brain twisting things about QM I'm starting to become aware of. 

So going straight to this tangent - does not the fact that we can see different colors of the rainbow imply, intrinsically, that different photons are different? 

 

(feel free to get philosophical, if you are willing to indulge my curiosity) 

[K^2]

21 minutes ago, JoeSchmuckatelli said:

So going straight to this tangent - does not the fact that we can see different colors of the rainbow imply, intrinsically, that different photons are different? 

They're different states. It might sound like pointless demagoguery, but it actually matters when you start counting possible states a system can occupy.

Say you have two coins. Each one can be heads or tails. You have 4 possible states. HH, HT, TH, or TT. But if you can't tell between the two coins - if they are truly indistinguishable on most fundamental level, then TH and HT are the same state, and there are only 3 possible states for the system. Elementary particles behave this way. You don't count exchanges as distinct states - they are all counted as a single state. And this actually has consequences on things like entropy of the system.

[kerbiloid]

8 hours ago, AHHans said:

Only if you make sure that all plastic bags are actually collected and recycled!
Oh, and you have a nice and clean way to generate the energy need for collection, transport, and recycling. But let's tackle the problem of making sure that none of the plastic winds up in the ocean first.

But look:
https://en.wikipedia.org/wiki/Great_Pacific_garbage_patch

The ocean is a natural reservoir of dispersed microscopic plastic particles, and they are available almost everywhere.

So, there is no problem with their collection, transport, and recycling. Just drop the plastic wastes into ocean, and the Nature will do the rest.

Then we can:

• fuel the ships right with the seawater, by separating the plastic  and turning it into kerosene for the ship engines.
• build coastal thermal powerplants burning the same seawater

No pipes, no aframaxes, just ocean.

8 hours ago, AHHans said:

And in a hot (> 0K) body you have lots of electrons that keep bumping into each other and thus forcing each other to take turns, that's where all your photons come from.

And what if the body consists of positive ions, held together by self-gravity (ionized hydrogen cloud) ?
No electrons, just protons.
It should still emit at least IR photons.

Edited May 22, 2021 by kerbiloid

[kerbiloid]

I just recalled just the perfect analogy for all those cable-based rotating orbital stations.

The old sexploitation thriller _{(can't recall the title, lazy to search on disks)} about the prison in jungles, where they had the so-called "Thatcher's football", by having two semi-filled plastic cans, chained to the prisoner's ankles.
The idea was to make the victim chaotically rush about, by kicking the cans, until he falls down.
The unpredictable movement of the CoM (from kicks and splashing water) was making it look like a rotating orbital station connected by ropes.

Edited May 22, 2021 by kerbiloid

[JoeSchmuckatelli]

6 hours ago, kerbiloid said:

I just recalled just the perfect analogy for all those cable-based rotating orbital stations.

The old sexploitation thriller _{(can't recall the title, lazy to search on disks)} about the prison in jungles, where they had the so-called "Thatcher's football", by having two semi-filled plastic cans, chained to the prisoner's ankles.
The idea was to make the victim chaotically rush about, by kicking the cans, until he falls down.
The unpredictable movement of the CoM (from kicks and splashing water) was making it look like a rotating orbital station connected by ropes.

There is a whole lot to unpack here. 

 

[SOXBLOX]

8 hours ago, kerbiloid said:

I just recalled just the perfect analogy for all those cable-based rotating orbital stations.

The old sexploitation thriller _{(can't recall the title, lazy to search on disks)} about the prison in jungles, where they had the so-called "Thatcher's football", by having two semi-filled plastic cans, chained to the prisoner's ankles.
The idea was to make the victim chaotically rush about, by kicking the cans, until he falls down.
The unpredictable movement of the CoM (from kicks and splashing water) was making it look like a rotating orbital station connected by ropes.

Happily, I can say I've not watched that.

[AHHans]

9 hours ago, kerbiloid said:

And what if the body consists of positive ions, held together by self-gravity (ionized hydrogen cloud) ?
No electrons, just protons.

Then you have a situation a describe here: Proton Earth, Electron Moon

Actually, most of the interstellar and intergalactic medium is ionized. Otherwise it wouldn't be transparent to photons above the ionization energy. But that means that you have an electron gas and a proton gas at essentially the same place, so that the net charge is neutral. In addition, the electron and proton gases can have different temperatures. And, yes, the proton gas will also radiate but protons are so much harder to convince to take a turn so that the electrons typically radiate more.

9 hours ago, kerbiloid said:

The ocean is a natural reservoir of dispersed microscopic plastic particles, and they are available almost everywhere.

May I introduce you to the concept of Entropy and the related problem of undoing it.

 

16 hours ago, JoeSchmuckatelli said:

So going straight to this tangent - does not the fact that we can see different colors of the rainbow imply, intrinsically, that different photons are different?

Well, photons of different color obviously have different quantum states. So, yes, they are different.
My comment was more: when you send out a photon from source A to detector B, does it matter if it is exactly the same photon or if it was destroyed and re-created in vacuum fluctuations on the way? As long as the photon that arrives at B has the same quantum state.

P.S. Are you sure that you want to follow this train of thought? I cannot guarantee that you'll get out with your mind intact if you keep following this.

[kerbiloid]

2 minutes ago, AHHans said:

May I introduce you to the concept of Entropy and the related problem of undoing it.

The whole ocean resource refining is based on dispersed ions filtering out.

Not that it's a source of energy. It's a transportation of energy.

Delivering it rght to the ships without pipes and tanks.

[AHHans]

1 minute ago, kerbiloid said:

The whole ocean resource refining is based on dispersed ions filtering out.

Are you sure?

And even for the minerals for which this is true, how large is the fraction that is actually filtered out?

[kerbiloid]

2 minutes ago, AHHans said:

Are you sure?

Li and U ions stick to the plastic nets, get washed from it, and processed.

Spoiler

 

 

Edited May 22, 2021 by kerbiloid

[AHHans]

Hmmm...

Care to also answer my other question? (About the fraction that is actually filtered out.)

Edited May 22, 2021 by AHHans

[kerbiloid]

1 minute ago, AHHans said:

Care to also answer my other question? (About the fraction that is actually filtered out.)

Watch the video: 0.17 mg of Li per liter.

Edited May 22, 2021 by kerbiloid

[AHHans]

Which video?

[kerbiloid]

Just now, AHHans said:

Which video?

That video.

(In my previous post)

Same about uranium and other metals, but in other sources.

[AHHans]

6 minutes ago, kerbiloid said:

Watch the video: 0.17 mg of Li per liter.

Well, I'm not holding my breath to see if this will be viable.

In the end it proves my comment about entropy.

[kerbiloid]

Just now, AHHans said:

Well, I'm not holding my breath to see if this will be viable.

In the end it proves my comment about entropy.

The more plastic in ocean - the easier to mine.

[JoeSchmuckatelli]

24 minutes ago, AHHans said:

Are you sure that you want to follow this train of thought? I cannot guarantee that you'll get out with your mind intact if you keep following this

Between your answers and @K^2 I'm starting to get a broad picture of the answer. 

When talking about the mathematical observation /theory, if you can't tell the difference between particles in the same state - even if measured at different times and places - there is no way to prove that you are not seeing the same particle twice. This does sound like a philosophy question and something that makes thinking about approximations easier. The reality is that you might be seeing two different particles or the same particle - but for the work / understanding you are trying to accomplish /achieve... It is a distinction that does not matter. 

Between this and responses to my past quibble about determinism and questions about Relativity & curved spacetime and 'folks in the know's' explanation that these are powerful, working mathematical approximations for what is really going on... I get a nice fuzzy picture for stuff I don't have the maths to winkle out for myself