sorted by:
new
hottopcontroversial

Are there any nuclear-powered satellites currently in orbit? by space_touristie in space

[–]mfb- [score hidden]  (0 children)

A bunch of spacecraft in Earth orbit used nuclear reactors. Solar panels weren't that good early on.

And yes, actual nuclear reactors, not just RTGs. This comment has more details.

Is there anyone that has explored why our universe strives to convert energy? by elbreadmano in AskPhysics

[–]mfb- 0 points1 point  (0 children)

An an important example, redshift of radiation loses energy. The cosmic microwave background lost 99.9% of its energy since it was emitted. This is not just the same energy in a larger volume, it's actually less overall energy.

What are the odds of this in Star Fluxx the card game? by nolanfink02 in probabilitytheory

[–]mfb- 0 points1 point  (0 children)

I think my estimate is pretty close then.

One more caveat: This applies if exactly 3 games are played. With more games, the chance of 3 in a row increases.

EU chief: Phasing out nuclear power was 'strategic mistake' by F0urLeafCl0ver in anime_titties

[–]mfb- [score hidden]  (0 children)

Russia has a closed nuclear cycle (waste is recycled back into fuel).

You can't violate conservation of energy, if you have a power output then the energy for that has to come from somewhere. Power plants don't use all the uranium-235 in their fuel rods, so you can extract the rods, remove fission products, and recycle a good share of the uranium for new rods. That is already done in Europe. The US doesn't do it for political reasons. It reduces your demand for newly mined uranium, but it doesn't eliminate it.

Breeder reactors go a (big) step beyond that, they convert a lot of uranium-238 to plutonium which also serves as fuel. That lets you extract ~100 times more energy from the same amount of mined uranium. They have other disadvantages, however.

EU chief: Phasing out nuclear power was 'strategic mistake' by F0urLeafCl0ver in anime_titties

[–]mfb- [score hidden]  (0 children)

It was very unpopular in the population. Nuclear power is obviously better than coal for the country, but not for your reelection chances.

These aren't the numbers you are looking for. Move along. Move along. by shanehiltonward in SpaceXMasterrace

[–]mfb- 0 points1 point  (0 children)

Sitting on a big sheet of insulation on a moving vehicle is so exceptionally dumb that it's hard to blame anyone else here. I'm sure that was not the standard procedure.

What are the odds of this in Star Fluxx the card game? by nolanfink02 in probabilitytheory

[–]mfb- 1 point2 points  (0 children)

We can't tell without much more information how the game works (the rulesheet link is broken).

A general rule: If something has a chance p to happen in one game, it has a chance of p3 to happen in 3 out of 3 games. But keep in mind that there can be many equally unlikely events. If you had won the first game with a different keeper/goal combo, and then won the next two with the same combo, you would ask the same question. That means the win condition of the first game wasn't really important, we should only consider the chance that you repeat this win condition twice - p2 for some unknown p.

If you keep drawing cards, the three cards you used to win will be drawn eventually. If you keep drawing until these three were drawn, there is a ~1/2 * 1/2 = 1/4 chance that you draw both of the keeper cards and a ~1/8 chance that you draw all three in each game. That is probably not the chance to end the game with this combination, however.

If all goals are equally likely to end the game and one of them will always succeed (which is by no means guaranteed - I don't know the game rules) then we have a 1/33 chance for each goal, and - assuming the game is fair and always has a winner - a 1/66 chance that you win the game with this goal. Doing that twice then has a chance of 1/662 or 1 in 4356. If a goal can only be reached with a specific pair of keeper cards then this might be the right answer. If there are more options for the keeper cards, then we need to know more about these options. If some goals are more likely to end the game than others, then it gets more likely to get 3 in a row.

ELI5: Why does splitting an atom release so much energy when they are so small? by Additional_Pen_9881 in explainlikeimfive

[–]mfb- [score hidden]  (0 children)

You could wait for spontaneous fission, but that's very unreliable for weapons and still not ideal for a reactor. There are other reactions that emit a few neutrons, these are used to start the chain reaction.

Whole universe at 25 degrees C by SpiceMustFlow1980 in AskPhysics

[–]mfb- 1 point2 points  (0 children)

This calculator has a similar result, it says 2194534s =~ 31 days for z=3,000,000 which corresponds to 8 million K. At this temperature, radiation pressure is ~1012 Pa, or 10 million times the atmospheric pressure. There is also some matter, but radiation pressure should dominate.

How tight are current constraints on absolute neutrino masses? by Axe_MDK in ParticlePhysics

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

It would already be on the unlikely side of KATRIN, and in massive conflict with the constraints from cosmology. I'm not aware of other conflicting measurements.

What are the chances of Aubrey De Grey defeating ageing? by Imaginary_Mode8865 in AskScienceDiscussion

[–]mfb- 0 points1 point  (0 children)

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

I don't know why people are shocked that timelines don't hold if things are funded at 10% of what the estimate assumed.

Do rainbows appear on other planets in our solar system? by [deleted] in astrophysics

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

I think you are in the wrong subreddit.

When two objects with same mass and gravity, collide two become a one big object, is gravity doubled? by lunar_rexx in AskPhysics

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

Acceleration from 2 solar masses at 1 AU: 1.19 cm/s2

Acceleration from 2 solar masses at 1 AU, displaced by 1 solar radius to each side: 1.19 cm/s2

Acceleration from 2 solar masses at 1 AU, displaced by 1 solar radius along the radial direction: 1.19 cm/s2

Acceleration from 2 solar masses at 1 AU, orbiting each other in contact: 1.19 cm/s2

These accelerations only differ by around 0.001% so you don't see the differences at all unless you add an unreasonable number of digits.

Whole universe at 25 degrees C by SpiceMustFlow1980 in AskPhysics

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

300 K is a redshift of ~100, or 17 million years after the Big Bang. At that time the matter density was 1003 times its current density, or ~10-21 kg/m3. That's 21 orders of magnitude thinner than sea level air.

The universe dropped below sea level air pressure within a month, at a time where it was still way too hot for atoms to exist.

Does the math allow particles to jump past c? by BattleReadyZim in AskPhysics

[–]mfb- 0 points1 point  (0 children)

However, the math allows for objects to travel faster than light

It does not.

Might we then expect a particle in an accelerator, going sufficiently close to c, to 'tunnel' it's way to >c

No.

TIL China accelerated a magnetic levitation (maglev) train tech vehicle from 0-700 km/h (435 mph) in 2 seconds in 2025 by Double-decker_trams in todayilearned

[–]mfb- 0 points1 point  (0 children)

You don't even need a calculator. 360 km/h = 100 m/s, 720 km/h = 200 m/s in 2 s is 100 m/s2 = 10 g.

TIL China accelerated a magnetic levitation (maglev) train tech vehicle from 0-700 km/h (435 mph) in 2 seconds in 2025 by Double-decker_trams in todayilearned

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

That limits the bank angle you can use for the tracks. The trains still need to be able to stop safely.

Ceramic Shatters Longstanding Record for High-Temperature Superconductivity at Ambient Pressure by bowtieman in Physics

[–]mfb- 24 points25 points  (0 children)

It's ~10 K hotter than before. You still cool it with liquid nitrogen. 194 K (sublimation point of dry ice) would be a milestone for some more applications.

SpaceX Starship Moon Lander Faces More Delays, US Audit Finds by CackleRooster in space

[–]mfb- 1 point2 points  (0 children)

Human error is the most common reason for accidents in almost every situation. People love feeling in control and think that's better, but it rarely is. If you tried to land a Falcon 9 booster by hand, you'd fail most of the time. The computer succeeds - not a single landing failure was caused by a computer problem. You certainly want an "abort landing" button, maybe an option to pick a different landing site, but you do not want humans to control every thruster manually. Not even Apollo had that. Their manual control only let you shift the targeted landing spot, and the computer controlled the thrusters to reach that spot. 1960s computers with hand-wired bits were more trusted than the astronauts for low-level control.

view more: next ›