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Nasa’s Roman Mission Will Hunt for Primordial Black Holes

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Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#51

Post by NegativeLatency »

pfdietz wrote: post #21
breckenedge wrote: post #3

I really want primordial black holes to turn out to be the missing antimatter from the Big Bang, but I don’t think that could ever be tested. And of course a mechanism for this would probably need new physics since antimatter interacts the same as normal matter wrt gravity.

There were suggestions that the antimatter-matter asymmetry is because antimatter was preferentially segregated into a dense phase of hadronic matter, like quark matter nuggets. This would be interesting because if such nuggets could be found and captured, they'd be a potential source of energy by annihilation with ordinary matter.

> preferentially segregated into a dense phase of hadronic matter

Sounds interesting, where can I read more theories about this?

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#52

Post by pfdietz »

NegativeLatency wrote: post #51
pfdietz wrote: post #21

Earlier quoted context omitted.

There were suggestions that the antimatter-matter asymmetry is because antimatter was preferentially segregated into a dense phase of hadronic matter, like quark matter nuggets. This would be interesting because if such nuggets could be found and captured, they'd be a potential source of energy by annihilation with ordinary matter.

> preferentially segregated into a dense phase of hadronic matter Sounds interesting, where can I read more theories about this?

Here's a recent (2021) paper on the idea: https://arxiv.org/abs/2105.08719

It has the nice feature of explaining why the density of baryons and the density of dark matter are not too different. Naively, there's no reason to expect the two to be anywhere close to each other. It also offers an explanation for the observed matter-antimatter asymmetry in the universe.

Don't believe any theory until it's been well tested.

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#53

Post by ralferoo »

jdminhbg wrote: post #27
hyperific wrote: post #20

NASA in the title should be all capital letters as it's an acronym and not a name.

Depends on where you live: https://proofreadingpal.com/proofreading-pulse/writing-guide... .

As a Brit, I've never noticed NASA spelt Nasa before, and I'm on the fence about Unesco, not because I recall seeing it title-caps, but because it doesn't look offensive to me.

That said, when I googled for the title-caps variants of both words, I saw the Guardian, Independent and Times all used it for Nasa, but only the Guardian and Times seem to use it for Unesco. There was also a page from the NYT that used Unesco, so a counter example from the US, but even the UK government pages refer to it in all caps, as do most other UK articles.

I certainly find it a weird generalisation that "UK English" (sic) prefers title-caps, as we tend to like our abbreviated names and pretty much always use all-caps when every letter comes from a separate word, and only title-caps when we use runs of letters from each different word - quango (quasi-NGO), Bakerloo (Baker St-Waterloo), Beeb (compared with BBC), Lib Dems, etc. We also have a few things that aren't consistent for government things - Defra (always used to be DEFRA, but they seem to have rebranded), MOD (always caps), Ofqual (=Office of Qualifications, always title case), Ofcom (=Office of Communications, now seems to officially be title case, but always used to be OFCOM), UCAS (University and Colleges Admission Scheme, always all-caps), etc.

Maybe the stylistic choice is based on how pronounceable it is as a word, but whatever I don't think there are any hard and fast rules!

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#54

Post by chefkd »

question for the initiated: why do space agencies divide their resources and attention between different projects? Wouldn't it make sense to focus first on making the moon and it's resources accessible kind of like airplanes then systematically expand to Mars, asteroid belt, and so on instead of spreading out too thin without conquering the closest

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#56

Post by LegionMammal978 »

ralferoo wrote: post #53
jdminhbg wrote: post #27

Earlier quoted context omitted.

Depends on where you live: https://proofreadingpal.com/proofreading-pulse/writing-guide... .

As a Brit, I've never noticed NASA spelt Nasa before, and I'm on the fence about Unesco, not because I recall seeing it title-caps, but because it doesn't look offensive to me. That said, when I googled for the title-caps variants of both words, I saw the Guardian, Independent and Times all used it for Nasa, but only the Guardian and Times seem to use it for Unesco. There was also a page from the NYT that used Unesco…

U.S. newspapers have a tendency to convert abbreviations to title case, even when everyone else uses all-caps. For instance, I've only ever seen "Covid-19" written in newspapers: everyone else always used "COVID-19", "COVID", or just "covid", or "the coronavirus".

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#57

Post by utensil4778 »

jebarker wrote: post #49
Tostino wrote: post #12

Earlier quoted context omitted.

Not necessarily. If you replaced the sun with an equivalent mass black hole, none of the orbits of the planets would change.

I'd like to see a simulation of what that would look like. I mean, if by magic the sun was replaced with an equivalent mass black hole in an instant would anything be visible from earth before the inevitable freeze?

From Earth's perspective, you wouldn't see anything interesting except for the sun vanishing. Gravitationally, all that matters is the absolute mass, so all the dynamics of the solar system stay the same.

A black hole of 1 solar mass has a radius of something like 3km. Totally invisible from Earth. You probably wouldn't even see any gravitational lensing. All we would see is the sun there one moment, and then nothing the next.

Life on Earth would continue for a while, but the planet would eventually freeze over.

So, nothing interesting. The sun vanishes and then some time later you freeze and/or starve to death.

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#58

Post by macintux »

chefkd wrote: post #54

question for the initiated: why do space agencies divide their resources and attention between different projects? Wouldn't it make sense to focus first on making the moon and it's resources accessible kind of like airplanes then systematically expand to Mars, asteroid belt, and so on instead of spreading out too thin without conquering the closest

Purely speculative:

- Betting everything on a single huge project is risky. You wait for years for completion, and if some critical part of the project costs more/takes longer than expected (much like Artemis today) you risk achieving nothing at all.

- Small, cheap projects that don't bankrupt the agency if they fail, when they succeed, generate ongoing positive PR and scientific results. NASA famously promoted this concept after one or two expensive projects had problems (of course, not famously enough that I remember more details).

- Some of those smaller projects are critical, like climate monitoring. You can't just set aside those sorts of tasks for a literal moonshot.

- Smaller projects contribute towards the big ones: NASA has given SpaceX a fair bit of money over the years that is paying off with Starship and Artemis.

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#59

Post by consumer451 »

hyperific wrote: post #20

NASA in the title should be all capital letters as it's an acronym and not a name.

HN automatically makes various changes to submission titles. The lesson that should be learned is that after submitting, there is a short period of time where the user can edit the title back to what it should be, in cases such as this.

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#60

Post by gus_massa »

MeImCounting wrote: post #28
vundercind wrote: post #25

Earlier quoted context omitted.

Star Trek fans will recognize the name as that of a versatile light starship class often seen acting as science vessels. https://en.m.wikipedia.org/wiki/Oberth_effect FWIW I’ve read several explanations of why this works, including some confidently claiming that one or more of the others was wrong, and a couple of which kinda made sense as I was reading them, but not a one of them has made a lick of sense to me after…

OK so I was totally confused by the Oberth effect and how it could possibly be and so did some research. Now I have no idea why or how kinetic energy has a quadratic relationship with velocity, but it does. Something something work something something square of velocity, who knows. If someone could explain that to me like I'm 5 I would totally appreciate it. But if we just take that as a given then we can develop an…

> ELI5 mv^2/2

Imagine a car is moving at a speed of 10 m/s. The driver hits the brakes. How much distance does it need to stop?

The main idea is that brakes have a constant force, and the change in speed is always constant. Let's say they reduce the speed in 1 m/s each second.

The first second the car travels 10 m and the new speed is 9 m/s.

The second second the car travels 9 m and the new speed is 8 m/s.

The third second the car travels 8 m and the new speed is 7 m/s.

...

The ninth second the car travels 2 m and the new speed is 1 m/s.

The tenth second the car travels 1 m and the new speed is 0 m/s.

So the total distance until it stops is 10+9+8+7+6+5+4+3+2+1. If you make a pile of bloks and you put first 10, then 9 over them, then 8 over them, .... you get a nice triange. The base is 10 and the heigh is 10, so the total number of blocks is 10*10/2. [1] [2]

So the car needs 10*10/2 m to stop. You can repeat the calculation with other initial speeds, and the result is V*V/2.

I'm not sure if it's intuitive, but the energy is proportional to the distance to stop.

Another posibility is to throw a toy car verticaly, and calculate how hight it goes. It's the same calculation. The maximal height is V*V/2. I think it's easier to imagine that energy is proportional to maximal height.

[1] If you actually count them, the result is 55 insted of 50, more details in https://en.wikipedia.org/wiki/Gauss_sum , but 10*10/2 is a good aproximation.

[2] If you split the time in half seconds and use smaller and smaller blocks, and then use calculus, you get 10*10/2.

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