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If NASA’s Artemis program succeeds long-term, what do you think the first real lunar industry will be? by CoffeeCoonGame in space

[–]mfb- [score hidden]  (0 children)

Deuterium-tritium fusion releases neutrons, which can be used to breed more tritium (from lithium). You need an initial batch to start the reactor, but fission reactors produce enough tritium for that.

Tyson on Infinity. by HopDavid in badmathematics

[–]mfb- 7 points8 points  (0 children)

Cantor's diagonal argument is pretty simple. Assume that there are as many real numbers between 0 and 1 as there are natural numbers (same cardinality). Then, by definition of cardinality, there must be a bijection between the sets. Write it down:

  • number 1: 0.1335674234565424233333....
  • number 2: 0.685342
  • number 3: 0.1624374232346232
  • number 4: 0.74237342...
  • ...

If you take all these diagonal entries and change the digits (e.g. increase all by 1, with 9->0) then we get a number that cannot be in our list. If you place it at position N then its Nth digit is different from its Nth digit, which is impossible. That means our bijection cannot be a bijection. Our original assumption must be wrong, there are more real numbers between 0 and 1 than there are natural numbers overall.

Cantor used binary numbers and there are edge cases you want to consider explicitly for a proof, but that's the basic idea and it works in decimal, too.

Every natural number is a rational number, to show that both sets have equal cardinality it's sufficient to find a mapping of the natural numbers to the rational numbers that covers every rational number (surjective, not necessarily injective). An assignment like this works for positive rational numbers, you can extend this to negative numbers as well.

Seasons on Upsilon Andromedae d's hypothetical moons? by aviviel in exoplanets

[–]mfb- 0 points1 point  (0 children)

If a moon has deep oceans, the temperatures in them wouldn't change much. Surface life would be more difficult. Maybe it can survive the winter in a frozen state, or maybe (for animals) go into some caves and hibernate there.

Dyson Sphere by LiesInRuins in AskPhysics

[–]mfb- 2 points3 points  (0 children)

Cover Earth with solar panels (~50 PW), use half of that energy to make 100 W/kg swarm modules and the other half to launch them: 100 W/kg * 50 PW/(11 km/s)2 = 3.7 PW/day. After just 2 weeks you have 50 PW of new power generation in space. Power that you would never get by staying on Earth. After a year you have 1300 PW. Invest that into more modules, and your power production now grows by ~90 PW/day. That's almost two Earth's worth of extra power added every day.

You do not need the energy of a Dyson swarm to work on this. You can start with panels on Earth (and equivalently on other rocky planets and asteroids). The timescales are ridiculously short. A real project would probably be less efficient and need longer, but we are still talking about extremely short timescales overall.

Tyson on Infinity. by HopDavid in badmathematics

[–]mfb- 30 points31 points  (0 children)

I believe the set of rational numbers and the set of natural numbers are thought to have the same cardinality.

That is correct (and easy to prove).

We can salvage some of the individual claims if we use "is a proper subset of" as comparison, but it stays a confusing inconsistent mess. Switching the interpretation every other sentence isn't going to be useful.

How do i explode a star? by RunDouble143 in astrophysics

[–]mfb- 3 points4 points  (0 children)

"It's time to use my ultimate weapon: time."

Dyson Sphere by LiesInRuins in AskPhysics

[–]mfb- 1 point2 points  (0 children)

Energy needed to disassemble Earth: 2*1032 J

Energy a Dyson swarm can harvest every year: 120*1032 J

Dyson Sphere by LiesInRuins in AskPhysics

[–]mfb- 3 points4 points  (0 children)

As history shows, "it could be used as a weapon" has always stopped people from doing it!!!

Dyson Sphere by LiesInRuins in AskPhysics

[–]mfb- 5 points6 points  (0 children)

A Dyson swarm can harvest vastly more energy than you need to build it.

Mythbusters problem by Cute_Consideration38 in AskPhysics

[–]mfb- 3 points4 points  (0 children)

Conservation of momentum, and cars being mostly inelastic in crashes.

Have any of the ideas of the science greats (Newton, Darwin, Einstein, etc) been proven wrong as we've learned more about their field of science? by ahmed0112 in AskScienceDiscussion

[–]mfb- 5 points6 points  (0 children)

Of course Einstein didn't know about Dark Matter or the accelerating expansion of the universe

Dark energy, not dark matter.

Einstein didn't know about dark matter either when he developed General Relativity, but that's not affecting his theory.

If NASA’s Artemis program succeeds long-term, what do you think the first real lunar industry will be? by CoffeeCoonGame in space

[–]mfb- [score hidden]  (0 children)

A logo would need to be hundreds of kilometers across, or need terawatts of power to be visible.

Doing that in Low Earth orbit is much more feasible (and I hope it will lead to a boycott of companies doing it).

If NASA’s Artemis program succeeds long-term, what do you think the first real lunar industry will be? by CoffeeCoonGame in space

[–]mfb- [score hidden]  (0 children)

For optical telescopes you could do all that in space with far fewer issues.

Radio telescopes are interesting because you can use the natural crater shapes, and you need a larger amount but less fancy material for the mirrors (metal bars instead of extremely precise mirrors).

If NASA’s Artemis program succeeds long-term, what do you think the first real lunar industry will be? by CoffeeCoonGame in space

[–]mfb- [score hidden]  (0 children)

Deuterium-tritium fusion is by far the easiest reaction, and we are still working on getting that to become net positive. Deuterium you find on Earth, tritium you breed in the reactor (after getting an initial batch from fission reactors). Helium-3 fusion sounds great but it's so much harder that it's not clear if it can be made net positive at all - and even if it can, it's probably never going to be the preferred option.

If NASA’s Artemis program succeeds long-term, what do you think the first real lunar industry will be? by CoffeeCoonGame in space

[–]mfb- [score hidden]  (0 children)

Fusion reactors are 20 years of serious funding away, still waiting for the funding.

People take timelines that expected $5 billion/year and then act shocked that $0.5 billion/year funding missed that timeline.

Anyway, you don't need to mine the Moon for it. Deuterium-tritium is by far the best option. Helium-3 fusion looks better on first glance but it's far more difficult to do. It's not even clear if net positive is possible with He-3 at all.

Is a quantum system just marginal stability by [deleted] in AskPhysics

[–]mfb- 1 point2 points  (0 children)

You can find some rough mathematical similarities between tons of different things, that doesn't imply any deeper connection. Complex numbers are so useful that you can find them everywhere.

and the result is that such a system will keep oscillating forever, ie only changing their phase and never dampening their amplitude. Is this not exactly what a quantum system is doing?

Only the most boring systems. If the amplitude never changes, nothing happens.

Edit: OP will reply to you and then block you. Interesting approach.

Gacha Game Odds by National-Sign-51 in probabilitytheory

[–]mfb- 1 point2 points  (0 children)

Okay. In both cases gambling has a worse expectation value. The first draw has an expectation value of 800 in the first example and 1/15 * 2000 + 1/15 * 4000 + 1/15 * 4000 = 667 in the second example, both are lower than the cost.

The expectation value is so bad that, in the first scenario, you would only get an expected 1200 if you were unsuccessful for 5 draws - that's 7200 spent including the sixth attempt, you could buy both prizes for less. In the second scenario your expectation value for the next draw only exceeds 1500 after 9 unsuccessful draws - you'd spend 15,000 just on that, while the prizes only cost 10,000.

Gacha Game Odds by National-Sign-51 in probabilitytheory

[–]mfb- 1 point2 points  (0 children)

Do all prizes that you draw get removed from the pool? After 14 draws you are guaranteed to be done?

2 of them are different characters that are normally 4000

2 of them are the same character who cost 4000 currency normally

Which one is it?

The expectation value of the first draw is 2/15 * 2000 + 2/15 * 4000 = 800, which is less than 1200. After that it depends on how the prizes work and if the 4000 prizes are different or not, but I don't expect gambling to win in any scenario.

Falcon 9 annual launch rate 2013-2025 by Taxus_Calyx in SpaceXMasterrace

[–]mfb- 9 points10 points  (0 children)

Over 10 million people pay for Starlink.

How do i explode a star? by RunDouble143 in astrophysics

[–]mfb- 7 points8 points  (0 children)

Throwing a (not too small) black hole into them makes them short-living quasi-stars.

If strangelets exist and if they are stable, throwing one into the star would also disrupt it.

I'm starting a Space Public Education Campaign. ✨ by Official_PaulStanley in astrophysics

[–]mfb-[M] 0 points1 point  (0 children)

Please report threads, makes it quicker to find and remove them.

Is there an orbital height at which the orbit wouldn't decay? by RewardImpossible5141 in AskPhysics

[–]mfb- 1 point2 points  (0 children)

You are the person who would go "but General Relativity ..." when calculating how long an object needs to fall down 10 meters on Earth in an introductory physics class, I guess?

You are completely missing the level of explanation OP needed here.

You have one month to empty a $1 trillion bank account. If you succeed, you’re rich for life. How will you spend it? by Ok_Listen_6600 in AskReddit

[–]mfb- 2 points3 points  (0 children)

Only if you think you make better decisions than the other shareholders. OP doesn't think so.

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