
Scientists Rule Out Hawking Theory for Source of Dark Matter - atentaten
https://www.popularmechanics.com/space/deep-space/a27048233/scientists-dismiss-hawking-theory-source-dark-matter/
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karmakaze
"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?

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castis
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

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

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Zenst
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.

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gus_massa
> _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

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Zenst
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](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](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.

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

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Zenst
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.

