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

by castis 8y ago

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

hprotagonist 8y ago
poke hard enough, and “assume” is the default for more or less anything more complicated than “I Know how to add two integers”.
- ScottFree 8y ago
  Engineering is science that has proven to be reliable and knowable. Engineering covers a whole lot more than adding integers.
  - hprotagonist 8y ago
    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=10.1371/journal.pcbi.1005268&type=printable https://journals.plos.org/ploscompbiol/article/file?id=10.13...
karmakaze 8y ago
Perhaps poorly phrased. I'd agree with the gravitational effects of unknown sources (aka dark matter) those of matter that we know of.
- Zenst 8y ago
  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.
  - gus_massa 8y ago
    > 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
    - Zenst 8y ago
      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.
      - karmakaze 8y ago
        How does inflation factor into calculation of gravitational force or speed of gravity wave propagation? Is it at a scale where it matters?
        Zenst 8y ago
        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.

by castis 8y ago

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

hprotagonist 8y ago

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

ScottFree 8y ago
Engineering is science that has proven to be reliable and knowable. Engineering covers a whole lot more than adding integers.
- hprotagonist 8y ago
  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=10.1371/journal.pcbi.1005268&type=printable https://journals.plos.org/ploscompbiol/article/file?id=10.13...

karmakaze 8y ago

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

Zenst 8y ago
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.
- gus_massa 8y ago
  > 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
  - Zenst 8y ago
    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.
    - karmakaze 8y ago
      How does inflation factor into calculation of gravitational force or speed of gravity wave propagation? Is it at a scale where it matters?
      - Zenst 8y ago
        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.