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5 votes
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The math of Emil Konopinski
7 votes -
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I have a basic and possibly uninformed question about the event horizon of a black hole
It is my understanding that if you are looking at an object falling into a black hole from a remote viewpoint, then the object will appear to take “forever” to complete the fall into the black...
It is my understanding that if you are looking at an object falling into a black hole from a remote viewpoint, then the object will appear to take “forever” to complete the fall into the black hole. The object is effectively frozen in time at the black hole’s event horizon, from the remote viewer’s POV.
Is this the correct interpretation so far? If so, let’s remember that.
It is also my understanding that a black hole can increase in mass as it captures new objects. The mass does increase from an external viewpoint. Is this accurate?
If I understand known science on the above points, then the paradox I see here is that while the visual information is frozen in time from the external POV, the mass of the black hole does increase from the external POV. So is this where the Holographic Principle comes in? Or is there another explanation here, or am I off-base entirely?
Or is it just that the accretion disk gains mass and black holes never increase in mass from an external POV, after they are initially formed?
Is this known?
Please either attempt to answer my tortured question, or point me to material that might lead me ask a better question.
Thanks!
13 votes -
Thorium Energy Conference 2018 - discussion of Molten Salt Reactor concepts and the new nuclear industry
12 votes -
Astrophysical detection of the helium hydride ion HeH+
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The most dangerous stuff in the universe - Strange stars explained
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Do black holes contain dark matter?
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LHCb sees a new flavour of matter–antimatter asymmetry
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The sideways tide
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Is the Earth flat?
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The double life of black holes: Perfect black holes are versatile mathematical tools. Just don’t mistake them for the real thing
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Visualization of quantum physics (quantum mechanics)
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Earth's magnetic pole is wandering, lurching toward Siberia
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Physicists stimulate Hawking radiation from optical analogue of a black hole
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CERN reveals plans for the Future Circular Collider (FCC) - almost four times longer than the current LHC
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Sean Carroll's Mindscape Podcast #28: Roger Penrose on spacetime, consciousness, and the universe
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New Horizons successfully explores Ultima Thule
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Amoeba finds approximate solutions to NP-hard problem in linear time
11 votes -
Quantum physics in a mirror universe
4 votes -
Scientists at the University of Oxford unifying dark matter and dark energy into a single phenomenon: a fluid which possesses 'negative mass"
27 votes -
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A layperson's introduction to Thermodynamics, part 3: Entropy and the heat death of the universe
Intro Hello everyone, Today we cover entropy and the heat death of the universe. The previous chapters can be found here and here. While I recommend you read both, you should at least read the...
Intro
Hello everyone,
Today we cover entropy and the heat death of the universe.
The previous chapters can be found here and here. While I recommend you read both, you should at least read the first part and skim the second.
A collection of all topics covered can be found here: https://tildes.net/~tildes/8al/.
Subject
Intro
Entropy describes how chaotic a system is. In thermodynamics, chaos is created from an irreversible process. We are all sort of familiar with this concept. A broken cup will not unshatter itself. As a consequence of how our universe works, (net) chaos can only increase. And this might have far reaching consequence, if we look at the effects of entropy on a cosmic scale.
Entropy
Entropy describes an amount of irreversible chaos.
But first, let's cover cycles super quickly. In thermodynamics, a very important concept is a "cycle". A cycle is a repeating process, that returns to its initial condition. For instance, when we ride a bike. We're turning our feet around the crank shaft. Repeatedly returning to the same position we started from. As we push on the pedal, some of our work is lost and turned into heat. Primarily due to friction from the wheels and from the different mechanical parts.
A cycle that wastes no energy is called a reversible cycle. That would mean 100% of the work in a cycle (even the work that is turned to heat) has to be returned in some way to its original state. The most famous example of this is the Carnot heat engine.[1] But in reality, the Carnot heat engine is nothing more than a theoretical engine. As we remember from before, we cannot turn 100% of heat back into work. So any heat engine, be it a car's motor, a refrigerator, a star, or the human body, will in some way contribute to this irreversible chaos.
Now what about entropy? If we look at entropy at the molecular level, it all becomes a bit abstract. But we can think of this concept with bigger building blocks than molecules, and still be close enough. Say you have a brick house with orderly layed bricks. This house would love to come crashing down. And lets imagine it does. When the house lays in ruins, it is not likely to suddenly "fall" into the shape of the house again. So if the house has collapsed, our system is in a higher state of chaos. Our entropy has increased. And unless we supply work to the system (and waste energy trough heat), we will not get the brick house back.
So now we understand, that on the grand scale of the universe, entropy will only increase.
The heat death of the universe
But what are the consequences of this? Imagine entropy going on for billions and billions of years. Everything in the universe slowly reaching a higher state of chaos. Everything that is orderly, turns into chaos. All high quality energy has turned into low quality energy. Everything has been wasted and turned into heat. Everything ripped apart until you are left with nothing to rip apart. At this point, there is no interactions between molecules any more. Everything has reached absolute zero temperature.
At this point, entropy is at its absolute maximum. And we have reached entropic equilibrium.
This is the heat death of the universe.
Afterword
Of course, the heat death of the universe is just one of the many theories about the end of the universe. It assumes that thermodynamics properly describes the universe, and that there are no hidden surprises.
Frankly told, it's the best bet we have with our current knowledge. But we still know so little. So I would not panic just yet. Alternatively, this is where we could continue with "an engineer's perspective on existensial nihilism". But I think that this is something better reserved for later, and better presented by someone else.
We have covered what I consider the absolute minimum of thermodynamics, that still gives us a basic understanding of thermodynamics. There are of course a lot of other topics we could cover, but thats it for now. I will potentially write an appendix later with some questions or things that have been asked.
But for now, that's it. Questions, feedback or otherwise?
Notes
[1] The Carnot heat cycle is a bit beyond the level of what we have discussed so far. It describes a system where heat is supplied and removed to have a piston expand and contract without any energy becoming waste heat.
14 votes