Ultimate space simulation software

 
User avatar
FastFourierTransform
Space Pilot
Space Pilot
Posts: 140
Joined: 17 Nov 2016

Science and Astronomy Questions

26 Nov 2017 09:01

Watsisname, Amazing explanation as always! I'm really gratefull. Talking with you is always very instructive.

I would have never thought that gravitational waves from exoplanets could be a feasible target for future observations!
It's true that calculations have to be done to get perspective, this goes againt my intuition.

I understand the background noise issue that would render the signals imposible to detach from others even if the strain is higher enough but couldn't this be overcomed? I mean, this could happen also with electromagnetic waves, but we are capable of isolating light from a source from the rest of bright objects of the universe. Maybe with several gravitational wave observatories source position in the sky could get as precise as modern optical astrometry (milliarcseconds). Also using fourier analysis we could extract the signal from each individual planet right?

I'm amazed by the fact that once the sensitivity for exoplanet detection is archived the planets of the Andromeda galaxy are just two orders of magnitude away from detection! this is awesome.

So, the biggest bias I see now is planetary distance. If the planet is close to the star the frequency and the amplitude of the garavitational radiation are both higher than for farther away exoplanets.
 
User avatar
Mosfet
World Builder
World Builder
Posts: 750
Joined: 24 Oct 2016
Location: Italy

Science and Astronomy Questions

26 Nov 2017 09:40

We will become the most frustrated life form of the universe, knowing all about planets around the galaxy, without a mean to actually go there in a life span. :D
"Time is illusion. Lunchtime doubly so". Douglas N. Adams
My mods | My specs: Asus x555ub - cpu i5-6200u, ram 4gb, gpu nvidia geforce 940m 2gb vram | IRC freenode.net canale ##SpaceEngineITA
 
User avatar
midtskogen
Pioneer
Pioneer
Posts: 421
Joined: 11 Dec 2016
Location: Oslo, Norway
Contact:

Science and Astronomy Questions

26 Nov 2017 10:16

If we know all about them, the need to go there is less pressing.
NIL DIFFICILE VOLENTI
 
User avatar
Mr. Missed Her
Astronaut
Astronaut
Posts: 61
Joined: 09 May 2017

Science and Astronomy Questions

27 Nov 2017 09:33

Has anyone seen my latest post? I'd like to know what I got wrong about thermodynamics.
Space is very spacious.
 
User avatar
midtskogen
Pioneer
Pioneer
Posts: 421
Joined: 11 Dec 2016
Location: Oslo, Norway
Contact:

Science and Astronomy Questions

27 Nov 2017 11:39

Missed her,

Perhaps there is a confusion about what an isolated system is? When you say that you're able to break the second law, how do you guarantee that your system is isolated?
NIL DIFFICILE VOLENTI
 
User avatar
FastFourierTransform
Space Pilot
Space Pilot
Posts: 140
Joined: 17 Nov 2016

Science and Astronomy Questions

27 Nov 2017 14:00

Mr. Missed Her wrote:
Source of the post The laws of thermodynamics aren't actually laws. They're correlations.

What exactly do you mean with this? The conservation of energy (first law of thermodynamics) is quite a law. Maybe you could say that the second law of thermodynamics is a principle or a statistical corollary. Better said: The increse of entropy happens because of the emergence of a statistical property that is accounted for by multiple interactions that follow the laws of physics (it is a statistical emergent property of the interaction of particles as dictated by Newton's laws of motion, for example). So yeah in that sense the second law doesn't add anything about fundamental physics since its an emergent property and its behaviour also exhibits emergence from simplier (more fundamental) rules (laws of nature), you are just observing the collective action of newton's laws (for example) in a complex many-component system. But this is missleading because the second law tells something more than what statistics tell about interacting particles in a newtonian framework (just to follow the same example): it tells us that the universe had low entropy in the begining, it tells us that the universe didn't started as a thermal soup but as a highly ordered state that has been degrading over eons and will for much more. So it can't be just a principle clearly (nor a "correlation").



Mr. Missed Her:
Source of the post Hey, what if you tried to reverse entropy by surrounding Earth with infra-red sensitive solar panels? (Let's assume that Earth has been teleported into the middle of a big void, because the Sun's march towards entropy is keeping entropy at bay here.) The solar panels would convert all Earth's radiated heat to usable energy, which could be stored in batteries. There would then be much lower entropy than before Earth cooled off. So, what would stop me from breaking the second law of thermodynamics?

You have assumed that "The solar panels would convert all Earth's radiated heat to usable energy" this is a supposition that breaks the second law. You are assuming a situation where the second law can be broken to demonstrate that the second law could be violated as a conclusion. If your conclusion is your premise then a self-contained circular reasoning has taken place, a circular reasoning independ and isolated from the real physics, therefore coherent in a sense even if detached from nature and its principles.
So your model doesn't work in reality because you never took into account the rules of nature in the first place. But if the question you are asking is really what impedes you from recycling all the energy with the solar panels - battery system then the answer is more complicated.

1) The 100% of the energy radiated from Earth can't be absorbed entirely by any "inert" device.
2) The 100% of the energy absorbed by the solar panels can't be stored in the chemical battery
3) The 100% of the energy stored in the battery can't be retrieved from it
4) The 100% of the retrieved energy from the battery can't be converted into usefull work without the need of an external source to the entire system.

All of these 4 points are not technical challenges that could be overcomed in hypothetical engineering breakthroughs but are consecuences of the second law. Each one of them.

For me is hard to explain in a clever way the step-by-step logical path from the second law to 1), 2) or 3) but I can see inmediatelly why the fourth is impossible (and therefore even if 1), 2) and 3) were overcomed you still couln't transform the 100% of radiated energy to usefull work since 4) would still hold).

Instead of the battery think about ina more general sense; think about any device that can store energy that then can be retrieved by plugging something into it or opening a valve or something. In this sense the battery is no different than a dam. You can store energy in a dam accumulating water on one side. The water level will rise until you fill the battery (fill the dam), and thus there's now a lot of mass at different heights to the top of the water. This means there is potential energy. So you have stored potential energy in this dam, the same you can store chemical potential energy in an electric battery. Now suppose you want to take energy from your repository and transform it into usefull work. Easy bussiness, you open a gate in the dam and while the potential energy stored leaks into kinetic energy (in harmony with the mass of water leaking through the gate) you profit from that kinetic energy of the water to pull the blades of a fan and then with gears and things like that you get your usefull work done (it could turn on a machine for breaking bricks, a mechanical computer, anything...).
Great, now: suppose that you when the water has transfered all the kinetic energy you wanted to the blades you think I should use it again, I should store the water in the top of the lake at the other side of the dam. The problem is that you require to lift the water from the ground against the gravitational dwell of Earth, or putted in another way, you have to inject energy into the water and store it as potential energy once again. So you need energy or work to do this. But you are clever and think "if the only goal of my water driven engine is moving the water to the top of the dam again I don't need an external energy source! I could use the energy from the dam to lift the water again inside the dam". This is perpetual motion. Notice that this doesn't violate the first law of thermodynamics (energy is conserved, no new energy is created, it is the same of the dam recycled to perform the job of re-storing the same energy), but as we are going to see it violates the second law. A bit of heat is realeased when the blades are pushed by the water, a bit of heat is released when the engine starts lifting the water again into the dam, a bit of heat is released when the door of the dam is opened, all this energy is been unused, we are loosing energy in all the steps of this "perpetual fountain". But hey! you might think we could make a robot follow the heat and take those crazy moving molecules to make them collide with little gears in a directed fashing and transform that heat into work (so 100% of the energy is reorganized into work), right? NO, the robot needs energy to perform this complex task, even the most efficient robot (no leaks of energy while working) is going to spend more energy in doing this work than the energy he can gathers from heat for a directed purpose. That is more energy than the one of the dam to make all the energy of it usefull, therefore you need to introduce an external source of energy (another dam to power the robot?).
A robot is an active device so its easy to see the problem here but what about "a passive device"? A thermal insulator atached to the leaks of heat in all the machinery could absorb the heat, like your universal solar panels, right? NO. The problem is that even if it can absorb all the heat (maybe putting more solar panels behind that absorb the small leaks from the first layer of solar panels?) the way it is transformed into work can never archive 100% efficiency once again. Why? heat gets released also from the solar panels (since they get hotter)--> suppose no!---> its the same: since you want to make usefull work from that heat perfectly trapped in your solar panels you have to make for example a steam engine with all that collected heat. Microscopic zoom!!!! now each crazy moving particle (heat trapped in the panels) has to push the water molecules with all the violence as to get them in a vapour state so steam can flow and power whatever you want to power with the, remind, leaked heat from the energy recycling process. In this collision heated particles with water many water molecules are going to aquire the energy of the others but also in the mean time the water molecules can bring part of their energy to the heated particles. More of this is expected while water and thermal insulator archive an equilibrium temperature, when this moment arrive you have your steam but you still have a lot of heat in the insulator that can't be estracted because the water is to hot now to absorb the heat from the other. Well you might think again---> let's change this water with cold water again (usign the fountain so its all self-contained) so the water can absorb the heat that the warmed water can't and is still in the thermal absorbant / solar panels- thing.---->Great!! but you still arrive at another equilibrium and now you have to change the water again to extract the tiniest piece of heat still trapped in your anti-heat-leakage device... So in the end you are constantly changing the water to extract work from every time more infinitessimal amounts of heat that are been leaked, this constant change of water requires energy, where are you going to take that energy? from outside is the only answer left.

No matter what you do, the energy gets dispersed or allocated in containers that can't release all of that energy again to perform some work, or better said: they can, but to do that you need more energy than the one you have in your closed system. The dam needs a river repletishing the energy lost, the battery needs to restore it's chemical potentials (even if you can recharge it forever) etc...

But hey, you might say once again---> you are supposing leaks of heat (even if you are trying to patch them with increasing rigour and compelx devices that need energy). What of we conceive a device that can make it without heat leaks!!?---> nice then entropy would stay constant in your ideal, immaginary world, an entropy decrease wouls still be impossible, you just reduced the rate at which entropy increases to cero, but you didn't reduced entropy (just the rate of change). In fact the rigorous statement of the second law is that entropy stays the same or increases but never decreases even in ideal mathematical worlds. And have in mind the fact that besides this reality is still worse (entropy always increase in nature) because even if you leak an infinitessimal amount of heat the fact that the cycle repeats dooms us all, that leaking would end in a soup of energy that can't be used for nothing at all, your engine would stop, your dam wouldn't change level etc...

In your model it would happen the same. Analogous examples can be done for each part of this story but with the devices you described in your model. In the end all would stop, even if your efficiency in 100%.
 
User avatar
Mouthwash
Explorer
Explorer
Posts: 156
Joined: 22 May 2017

Science and Astronomy Questions

27 Nov 2017 20:29

I have a couple questions involving the online web serial Worm:

1. One character creates "a projectile so hyperdense that its gravitational field pulled cars behind it" to fire at an opponent. Is it possible for something to have enough mass to overcome Earth's gravitational field for, say, a few meters around it, without actually having a comparable mass to the Earth? Could gravity even work that locally?

2. At least two characters are capable of freezing time; the way it's presented in the story is that objects just stay frozen where they are and can't be moved or harmed by anything (I know what you're thinking, but there actually is a rational explanation for them staying at their positions relative to the Earth). But if I were to stop time for a certain area in real life - or if that's impossible, slow it down to the point that it makes little difference - what would it look like to us? Would frozen objects actually be invulnerable? Would light just bounce off of them, or would it build up on the edges until they were hotter than anything in the universe?

"Again half correct. :)

The infinite time dilation is relative to an observer far away.  If we drop a wristwatch into a black hole from far away, we first see it first accelerate as it falls deeper into the gravitational well.  But then something curious happens.  Near the horizon it will start slowing down, and gently come to rest on the horizon an infinite time later.  Weird!  But even weirder is that if we read the time on the watch, we see that it does not read an infinite time later!  As it slowed down near the horizon, it also began ticking more slowly, the rate decreasing exponentially closer to zero.  We can wait a million years, yet the watch would still read (if we could read it -- the light coming from it is also redshifted to blackness) only a very short time elapsed since we dropped it.

All of this so far is true.  And it is very tempting to think "time slows down and stops at the horizon, therefore if you fall in, your trip takes an infinite time and the hole evaporates in front of you."  But that part is wrong! 

That the wristwatch does not report an infinite time elapsed to the horizon is the clue.  The wristwatch is reporting what we call "proper time", the elapsed time that an object measures in its own frame of reference.  That the watch reads a finite and short time elapsed on its trip to the horizon suggests there is a part of its journey that we are missing.  Afterall, no observer directly experiences the effects of time dilation!  If you're on a rocket ship flying past Earth at nearly the speed of light, everyone on Earth says your clocks tick very slowly.  But do you see your clocks ticking slowly?  Do you move in slow motion and speak in slow sentences?  No!  

Similarly, if we fall in along with the wristwatch, we will not see the wristwatch ticking slowly.  We do not come gently to rest on the horizon.  We do not see universe time leap ahead to infinity. 

We fall straight through the horizon and end up at the singularity.  Long before the black hole evaporates.

Let's summarize these two wildly different experiences again briefly:

From outside the hole, we say objects slow down and vanish from view near the event horizon(This is gravitational time dilation and gravitational redshift -- they are the same effect.)

Falling in ourselves, we say everything falls through the horizon and ends up at singularity in a very short proper time.  We do not see time go to infinity, and the black hole's evaporation does not save us from our destruction at the singularity.  (And this is true for any particle, not just a human being)."


Hold on, you haven't explained why this is the case at all. Your description of a watch falling into the black hole is pretty much what I said (I never meant to imply that you would *perceive* yourself slowing down, only that the entire history of the universe would flash before your eyes and the black hole would shrink and evaporate just as you hit it).

My entire argument hinges on the time discrepancy between the outside observer and observer falling in. From the former perspective, we would see the black hole evaporate in a finite amount of time. Why wouldn't this be seen by someone for whom that time appears sped up indefinitely?
Last edited by Mouthwash on 30 Nov 2017 18:41, edited 4 times in total.
 
User avatar
Watsisname
Science Officer
Science Officer
Posts: 971
Joined: 06 Sep 2016
Location: Bellingham, WA

Science and Astronomy Questions

28 Nov 2017 02:27

Mouthwash wrote:
Source of the post(I never meant to imply that you would *perceive* yourself slowing down, only that the entire history of the universe would flash before your eyes and the black hole would shrink and evaporate just as you hit it).  Why wouldn't this be seen by someone for whom that time appears sped up indefinitely?


Because they do not see time sped up indefinitely!

For them to see time sped up indefinitely, an infinite number of light pulses would have to catch up to them.  But the trip to and through the horizon takes place in a very short time as measured on their clock.  Therefore there is only a very short time for which light can catch up to them!  Their experience of time passing in the outside universe, and for the black hole itself, is quite normal.  They don't enjoy the future evolution of the universe and the black hole doesn't evaporate in front of them.

If you are comfortable with space-time diagrams, they provide the easiest way to visualize this. I'll use one from the text "Exploring Black Holes" by Taylor & Wheeler.  This shows the world lines of a set of observers who are freely falling into a black hole (the book calls these "rain plungers", by analogy to rainfall), as well as the world lines of a regular series of light pulses also sent in from far away:

Image

The vertical axis is time, the horizontal axis is space.  The black hole's horizon is located at r/M = 2 (meaning r=2GM/c^2 in conventional units).  The black hole's singularity is at r/M = 0.

Consider the observer falling in who sees a pulse of light pass them at r/M = 4 (twice the horizon radius), at the chosen starting time t=0.  Before they cross the horizon, they will observe the next two light pulses.  And they'll see one more light pulse within the horizon.  But they never see any pulses after that.  The pulse which crossed r/M = 8 at t=0 never reaches them.  That observer hits the singularity first.  

This is why if you fall into a black hole, you don't see the universe's evolution go by in a flash, and you are not saved by the black hole's evaporation.

Another consequence and way of thinking about this:

If you watch someone fall into a black hole from a safe distance, you can still send signals to them.  They can even receive some of those signals when they are inside the horizon.  However, if you wait too long, then you will be unable to send signals to them.  Even though you say they never cross the horizon!  They say they crossed the horizon and will hit the singularity before those signals can reach them.
 
User avatar
Watsisname
Science Officer
Science Officer
Posts: 971
Joined: 06 Sep 2016
Location: Bellingham, WA

Science and Astronomy Questions

28 Nov 2017 03:38

Mouthwash wrote:
Source of the post 1. One characters creates "a projectile so hyperdense that its gravitational field pulled cars behind it" to fire at an opponent. Is it possible for something to have enough mass to overcome Earth's gravitational field for, say, a few meters around it, without actually having a comparable mass to the Earth? Could gravity even work that locally?

Indeed it can!  It would take a pretty insanely dense object, but it doesn't have to be as massive as Earth.

The gravitational acceleration at the surface of an object of mass M and radius R is 

[math]

Set a = g = 10m/s^2, and replace M with a relation between the radius and density [math] of the object:

[math]

and solve for density,

[math]

This tells us the threshold density for an object of radius R to have a surface gravity equal to g.  A density greater than that may have stronger gravity at larger distances.  Let's let R = 1cm for starters -- a reasonable size for a projectile?  Then to have 1g of gravity on its surface the projectile needs a density of 3.6x109 grams per cubic centimeter!  This is about 100,000 times denser than a white dwarf!  But not as dense as a neutron star.  Still, that's a bit scary.  It implies some really bad consequences, which we'll see more clearly in a moment.

This was just the condition to have a surface gravity of g on the projectile.  You want something exceeding g at several meters distance!

Let's let the projectile still have a radius of 1cm, but gravitational acceleration a=100m/s^2 = 10g at 10m.  Something that will definitely pull objects like cars behind it.  Since gravitational acceleration follows 1/r2, this means we need a=1000g at 1m (yikes), and a=10,000,000g at the surface of the projectile (very yikes).  This won't just pull cars behind it.  It will instantly crush them, and any victims caught too close to it, into the projectile itself!  This is a dangerous object the character has in his possession.

What kind of density does this projectile have now?  To have 10 million g at 1cm requires a density of about 3.6x1016 g/cm^3.  That's greater density than a neutron star!  But despite this great density it is not a black hole.  The Schwarzschild radius of this object is smaller than an atom.

We can make these numbers a bit less extreme by making the projectile a bit bigger.  If we make it a 10cm projectile, then to have 10g at 10m it must have a surface gravity of 100,000g, and a density of ~1013 g/cm^3.  Still denser than a white dwarf, but at least not as dense as nuclear matter, and thus a little bit less absurd.  I still wouldn't want to play with such a thing. :P


Added:  One more useful fact to consider: In all situations where the gravitational pull is the same at the same distance outside the projectile, the projectile's mass must also be the same.  For 10g at 10m, that's 1.5x1014kg, which is less than the mass of Phobos.  For a given mass of projectile, what may vary is its size, density, and surface gravity.  This is an important property of gravitational field outside a sphere. This is why you could collapse the Sun into a black hole yet not affect the orbits of the planets, while the gravitational field within the Sun's former radius would become stronger.
 
User avatar
Gnargenox
Pioneer
Pioneer
Posts: 396
Joined: 11 Dec 2016
Location: 179° 56′ 39.4″ +0° 2′ 46.2″ @ 7,940 ± 420 pc

Science and Astronomy Questions

28 Nov 2017 09:15

A study of the sensitivity to continuous-wave strain fields of a kg-scale opto-mechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity.

This narrowband detection scheme can operate at very high Q-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1–1.5 kHz range.  

The pressurization of helium makes this possible without affecting the damping rate, making the detector both narrowband and tunable.

Detecting continuous gravitational waves with superfluid 4He
CPU: AMD FX-8350 8 core processor 4GHz / GPU: GeForce GT 730 @ 1920x1080, 60Hz with 1GB adapter RAM / RAM: Patriot Signature 4GB 1600MHz 240-Pin DDR3 (only 2GB work, don't buy it) / Motherboard: MSI 970 Gaming MS-7693
 
User avatar
Mr. Missed Her
Astronaut
Astronaut
Posts: 61
Joined: 09 May 2017

Science and Astronomy Questions

28 Nov 2017 11:23

FastFourierTransform wrote:
Mr. Missed Her wrote:
Source of the post The laws of thermodynamics aren't actually laws. They're correlations.

What exactly do you mean with this? The conservation of energy (first law of thermodynamics) is quite a law. Maybe you could say that the second law of thermodynamics is a principle or a statistical corollary. Better said: The increse of entropy happens because of the emergence of a statistical property that is accounted for by multiple interactions that follow the laws of physics (it is a statistical emergent property of the interaction of particles as dictated by Newton's laws of motion, for example). So yeah in that sense the second law doesn't add anything about fundamental physics since its an emergent property and its behaviour also exhibits emergence from simplier (more fundamental) rules (laws of nature), you are just observing the collective action of newton's laws (for example) in a complex many-component system. But this is missleading because the second law tells something more than what statistics tell about interacting particles in a newtonian framework (just to follow the same example): it tells us that the universe had low entropy in the begining, it tells us that the universe didn't started as a thermal soup but as a highly ordered state that has been degrading over eons and will for much more. So it can't be just a principle clearly (nor a "correlation").

Oops, I wasn't thinking about the first law. Conservation is definitely a law (though the quantum vacuum raises some questions). Though the other laws, especially the second, I consider correlations. Though if the second law says "entropy tends to increase and never decrease," then I'd call it a law, because it acknowledges the probabilisticness in the statement. It's not how I see the law stated often.
As for the rest of your post, FastFourierTransform, I've mostly heard it before. The impossibility of 100% efficiency sure does help entropy, and entropy will eventually conquer everything. I know that. What I'm getting at is that the second law clearly states that entropy can never decrease, yet I can convert supposedly pure entropy heat into usable energy with my solar panel method.
But I think you might be trying to say something else: Because of the inherent lack of efficiency of everything, I can't convert enough heat to usable energy to actually decrease entropy. But that idea seems odd, because there isn't anything fundamentally impossible about making things more efficient. I don't think the laws of the universe prohibit me from making an 80% efficiency solar panel. And for the second law to hold in this case, it would have to be impossible to improve solar panel efficiency past a certain point.
Space is very spacious.
 
User avatar
FastFourierTransform
Space Pilot
Space Pilot
Posts: 140
Joined: 17 Nov 2016

Science and Astronomy Questions

29 Nov 2017 00:14

Mr. Missed Her wrote:
Source of the post As for the rest of your post, FastFourierTransform, I've mostly heard it before. The impossibility of 100% efficiency sure does help entropy, and entropy will eventually conquer everything. I know that. What I'm getting at is that the second law clearly states that entropy can never decrease, yet I can convert supposedly pure entropy heat into usable energy with my solar panel method.

Okay, two things here before answering.

1) It's very important to not confuse entropy with the second law of thermodynamics wich states the behaviour of entropy. It can be tricky I think.

2) There is no entropy heat. There is energy with more or less entropy.

But besides these unimportant points I have to say that my long post was in fact a bit confusing. I talked a lot about the fact that things can't be 100% efficient, but the main point is not that indeed. The main point is that even if you transformed energy into work 100% efficient entropy of the system would not decrease. You would only be able to decrease it if you used more energy that the one you have in your closed system. You could archive a "higher order state" just if you collected and used every bit of energy that the dismantelling of that state released and added a bit more of energy from outside to complete the task.

I would think about better and more synthetic examples, but this is the main point I want to acknowledge.
 
User avatar
Watsisname
Science Officer
Science Officer
Posts: 971
Joined: 06 Sep 2016
Location: Bellingham, WA

Science and Astronomy Questions

01 Dec 2017 04:33

Mr. Missed Her wrote:
Source of the post But I think you might be trying to say something else: Because of the inherent lack of efficiency of everything, I can't convert enough heat to usable energy to actually decrease entropy. But that idea seems odd, because there isn't anything fundamentally impossible about making things more efficient. I don't think the laws of the universe prohibit me from making an 80% efficiency solar panel. And for the second law to hold in this case, it would have to be impossible to improve solar panel efficiency past a certain point.

I think it can be broken down into two concepts.  The key is to think about what a solar panel is, at its most fundamental level.  It is a device which converts electromagnetic energy into electric potential energy.  How does a solar panel do this?  When it absorbs a photon, that photon's energy is used to move electrons around, thereby creating a charge separation, and thus a potential difference that can later be used to draw a current from.

Problem 1:  There is some minimum energy required to cause the charge separation.  If the absorbed photon does not pass this energy threshold, then it will simply produce heat.  It will do zero useful work.  This is one reason why you cannot have 100% efficiency in a solar panel.  Another reason is that not every photon absorbed will go into moving charges around, even if they have the required energy.  It might just be absorbed into an atom which is only a structural element of the panel, again serving only to increase the heat.  You cannot build a structure where every single photon that hits it is absorbed in a way that promotes power generation.

You might still think this isn't actually a problem.  That any photons that don't generate power will increase the heat to the point that the heat is re-radiated as sufficiently high energy photons, and therefore you get more chances of energy being re-absorbed "correctly" later on.  

Problem 2:  Your sphere of solar panels surrounding Earth will re-radiate that heat both inward and outward!  The heat radiated outward is lost to space, and you cannot prevent this.  This is related to midtskogen's suggestion, that we think carefully about how the system is defined.  If we define the system to be the sphere of panels with the Earth inside, we cannot prevent it from radiating energy outward, which means it is not a closed system.

This combination of the impossibility of 100% conversion of photons to electric potential energy, and the inability to prevent heat being lost to space, is why you can't use the Earth's infrared radiation to generate power and reverse the increase in entropy.  The 2nd law wins.

One more bit of insight, and a result of Problem 1, is that Earth's infrared emission is already too low in energy (too long in wavelength) to generate power in a solar panel.  If you don't believe me, try standing next to a solar panel in a darkroom, and generate power with your body heat.  You will get zero power.  The photons of your infrared radiation peak at a wavelength which is about 10 times too long for a solar panel to use.  This is one way in which you can directly see the consequences of the 2nd law in the energy re-emitted from Earth.  The re-emitted energy has already lost its usefulness for doing work.
 
User avatar
Mr. Missed Her
Astronaut
Astronaut
Posts: 61
Joined: 09 May 2017

Science and Astronomy Questions

04 Dec 2017 09:40

Watsisname wrote:
Source of the post Problem 1:  There is some minimum energy required to cause the charge separation.  If the absorbed photon does not pass this energy threshold, then it will simply produce heat.  It will do zero useful work.  This is one reason why you cannot have 100% efficiency in a solar panel.  Another reason is that not every photon absorbed will go into moving charges around, even if they have the required energy.  It might just be absorbed into an atom which is only a structural element of the panel, again serving only to increase the heat.  You cannot build a structure where every single photon that hits it is absorbed in a way that promotes power generation.

Ah, so there is a fundamental limit on solar panel efficiency. This means that if the fundamental limit is below a certain point, my sphere will be radiating too much for the energy I absorbed to have decreased entropy. And converting any amount of heat to usable energy doesn't necessarily decrease entropy, because as FFT pointed out, not all heat is pure entropy.
However, I could add better insulation. If nothing else, I could just keep adding layers to keep more heat in. But solar panels can't harvest light below certain wavelengths, so the panels should eventually stop absorbing energy. But won't fluctuations in heat produce sufficiently high-energy photons? My insulation prevents the heat from going anywhere else, so such fluctuations would eventually send out all the heat energy as absorbable photons. So what goes wrong with my plan here? A fundamental limit on battery life?
Space is very spacious.
 
User avatar
Mouthwash
Explorer
Explorer
Posts: 156
Joined: 22 May 2017

Science and Astronomy Questions

06 Dec 2017 16:16

Are there any known celestial bodies that can be (A) destroyed, or (B) have some part of themselves (atmosphere, solid layer) destroyed by a chain reaction? This occurred to me as I was reading about the theory that Saturn might be turned into a giant fireball by the Cassini probe's plutonium fuel. Of course it's not based on reality, but I was wondering if any such phenomenon is theoretically possible somewhere... it's a big universe, after all.

Who is online

Users browsing this forum: No registered users and 1 guest