Scientists Rule Out Hawking Theory for Source of Dark Matter | Hacker News Reader

Scientists Rule Out Hawking Theory for Source of Dark Matter

popularmechanics.com

17 pointsatentaten15 comments

"If Hawking's hypothesis was right, then you'd expect to see around a thousand such flickers. They saw one."

How is this expectation of 1000 derived? Was it based on the mg mass, what if they were 0.1 mg black holes?

Scientists know the mysterious substance makes up the majority of all matter in the universe, vastly outnumbering normal matter like stars, planets, and people.

s/know/assume

poke hard enough, and “assume” is the default for more or less anything more complicated than “I Know how to add two integers”.

Engineering is science that has proven to be reliable and knowable. Engineering covers a whole lot more than adding integers.

I mean, our axioms are pretty solid. They are axioms, though.

I like the gradations of “understanding” given here: https://journals.plos.org/ploscompbiol/article/file?id=10.13...

Perhaps poorly phrased. I'd agree with the gravitational effects of unknown sources (aka dark matter) those of matter that we know of.

Given the speed of light is 299 792 458 meters per second and current measurements for the speed of gravity is between 2.55 × 10^8 and 3.81 × 10^8 meters-per-second.

Then over distance we would see the effects of gravity from objects that we have yet to see. For example our Sun, the light you see has taken about 8 minutes to reach you. Yet the effects of gravity from the sun reach in about 6 minutes. As we know, the sun in the scale of the universe is extremely close. Scale that difference over distance and minutes become days, weeks, years, centuries...

So when it comes to gravitational effects from unknown sources, may be that they are from sources that we won't see for a long long time in the future.

> For example our Sun, the light you see has taken about 8 minutes to reach you. Yet the effects of gravity from the sun reach in about 6 minutes.

I think you misunderstood. As far as we guess from the theories, the speed of light an the speed of gravity is the same. The problem is that it is very difficult to measure the speed of the gravitational waves.

The experimental results for the speed of gravity has a wide interval. This interval includes the speed of light and we guess that they are the same, but it would be nice to have an experimental result with a nice small interval.

8 minutes vs 6 minutes: Nah

Yes we still don't know exactly the speed of gravity and as it stands we know it to be the around the same speed of light with a margin of 70% ( https://arxiv.org/abs/1602.04188 ). But with so many theories at play, we still don't know for sure. Indeed, some still believe that the speed of light has changed over time - hence https://en.wikipedia.org/wiki/Variable_speed_of_light . Which as a theory, if true, would really mess up distant astronomy calculations for some.

As you say, would be nice to have some definitive experiment that reduced the margin for error and give a more definitive speed for gravity. Though current results do tend to lean towards Einstein being right more than Newton in respect to the speed of gravity.

How does inflation factor into calculation of gravitational force or speed of gravity wave propagation? Is it at a scale where it matters?

How does expansion effect gravity, I don't know exactly. Does it stretch it as the same with light. Whilst light comes in various wavelengths, gravity as far as we know - does not. But a wonderful question and one day we will know for sure.

As with scale - difference would become more pronounced at scale.

An interesting thought I'd never read about though I thought the speed of gravity waves was further constrained to 2.993 × 10^8 and 3.003 × 10^8, but any difference is sufficient.

The part I don't follow is that light follows the curvature of space-time and it's the distortion of space-time that propagates at the speed of gravity. Even if this distortion propagated at 10 m/s the path of light and the path of gravitational attraction would be along the same lines of acceleration.

Light can be affected by gravity, I'm not aware of gravity being affected by light. Hence a distant objects gravity and light emissions would potentially travel different paths thru space over time.

We"ew talking about the speeds of light and gravity waves but if they don't take the same paths isn't directly comparable.

A black hole generates gravity waves that distorts space but light can't follow such a path. What path from a black hole do gravity waves take?

I was talking about the speed of light and gravity - even if the same - both are effected differently as your block hole example highlights. Take the light from a distant planet that passes near a black hole. That would bend the light and if too close - bend it into the black hole itself. Gravity from what we know would not be effected by that and as such - both light and gravity from that planet would take a different path.

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