3 ms·

"This extrapolation predicts that the cosmos should currently be expanding at a rate of 67.4 km/s/Mpc, with an uncertainty that’s less than 1%." I can't measur

"This extrapolation predicts that the cosmos should currently be expanding at a rate of 67.4 km/s/Mpc, with an uncertainty that’s less than 1%." I can't measure my own weight with an uncertainty that's less than 1%. I wonder what these peeps are on...

uncivilized 2y ago
Their wallets are much bigger than yours.
- readthenotes1 2y ago
  As is what they are trying to measure. I don't believe 1% measurement error in any universal element except perhaps the speed of light...
  - aidenn0 2y ago
    That's an absurd statement. For example, planck's constant is known to better than 1%, as is the mass of various particles. Heck, the Earth, which is sufficiently non-spherical for it to matter only differs in radius (between polar and equatorial) by 0.3%!
  - munchler 2y ago
    I suggest you take a look at this list of physical constants, paying special attention to the "uncertainty" column, and then get back to us on why you don't accept any of them except the speed of light. https://en.wikipedia.org/wiki/List_of_physical_constants https://en.wikipedia.org/wiki/List_of_physical_constants
  - bloak 2y ago
    Here's a nice list: https://en.wikipedia.org/wiki/List_of_physical_constants https://en.wikipedia.org/wiki/List_of_physical_constants G (the gravitational constant) is an interesting one: the value is only known to about 5 significant figures, but GM (the gravitational constant multiplied by the mass of the Earth) is known a lot more accurately, unsurprisingly, considering how well GPS works. Some of those constants seem to be known to about 12 significant figures.
  - dotnet00 2y ago
    If you can measure the speed of light extremely precisely, you can measure a lot of constants extremely precisely.
deleted 2y ago
[deleted]
shagie 2y ago
Depending on which end of the scale you are interested in, the NIST would be an interesting place to work. How To Measure The Tiniest Forces In The Universe https://youtu.be/pXoZQsZP2PY https://youtu.be/pXoZQsZP2PY and World's Heaviest Weight https://youtu.be/_k9egfWvb7Y https://youtu.be/_k9egfWvb7Y - both from Veritasium. From the expanded description on the heaviest weight: > Before visiting NIST in Washington DC I had no idea machines like this existed. Surely there's an accurate way to measure forces without creating such a huge known force?! Nope. This appears to be the best way, with a stack of 20 x 50,000 lb masses creating a maximum force of 4.45 MN or 1,000,000 pounds of force. I also wouldn't have thought about all the corrections that need applying - for example buoyancy subtracts about 125 pounds from the weight of the stack. Plus the local gravitational field strength must be taken into account. And, the gravitational field varies below grade. All of this must be taken into account in order to limit uncertainty to just five parts per million (.0005%)
itishappy 2y ago
Skill issue.
gangorgasm 2y ago
What is "Mpc"., if anybody knows?
- 613style 2y ago
  megaparsec (1 million parsecs)
  - gangorgasm 2y ago
    Thanks much
- tyfon 2y ago
  It is a distance unit, megaparsecs. Or approximately 3.25 million light years.
  - gangorgasm 2y ago
    Appreciated. Big distance I have difficulty conceptualizing "distance over time ... over [huge] distance" I guess it means "chunks about so [megaparsecs] large are moving [themselves] at a speed of so many Km. per second" but I could be wrong
    - tyfon 2y ago
      The measurement for expansion is linear with distance, so two spots one Mpc from another moves away front each other at 67.4 km/s while two spots two Mpcs from each other moves at 134.8km/s. This means the expansion is accelerating and some parts of the now visible universe will eventually move away from us faster than the speed of light resulting in them disappearing from our view. The distances, time and speeds are indeed very hard to comprehend from our usual references :)
      - gangorgasm 2y ago
        It's crazy that some parts of the universe will actually for all purposes vanish Thanks for taking time to break it all down
halayli 2y ago
Reading your very confident response it makes me wonder the same about you.

uncivilized 2y ago

Their wallets are much bigger than yours.

readthenotes1 2y ago
As is what they are trying to measure. I don't believe 1% measurement error in any universal element except perhaps the speed of light...
- aidenn0 2y ago
  That's an absurd statement. For example, planck's constant is known to better than 1%, as is the mass of various particles. Heck, the Earth, which is sufficiently non-spherical for it to matter only differs in radius (between polar and equatorial) by 0.3%!
- munchler 2y ago
  I suggest you take a look at this list of physical constants, paying special attention to the "uncertainty" column, and then get back to us on why you don't accept any of them except the speed of light. https://en.wikipedia.org/wiki/List_of_physical_constants https://en.wikipedia.org/wiki/List_of_physical_constants
- bloak 2y ago
  Here's a nice list: https://en.wikipedia.org/wiki/List_of_physical_constants https://en.wikipedia.org/wiki/List_of_physical_constants G (the gravitational constant) is an interesting one: the value is only known to about 5 significant figures, but GM (the gravitational constant multiplied by the mass of the Earth) is known a lot more accurately, unsurprisingly, considering how well GPS works. Some of those constants seem to be known to about 12 significant figures.
- dotnet00 2y ago
  If you can measure the speed of light extremely precisely, you can measure a lot of constants extremely precisely.

deleted 2y ago

[deleted]

shagie 2y ago

Depending on which end of the scale you are interested in, the NIST would be an interesting place to work. How To Measure The Tiniest Forces In The Universe https://youtu.be/pXoZQsZP2PY https://youtu.be/pXoZQsZP2PY and World's Heaviest Weight https://youtu.be/_k9egfWvb7Y https://youtu.be/_k9egfWvb7Y - both from Veritasium. From the expanded description on the heaviest weight: > Before visiting NIST in Washington DC I had no idea machines like this existed. Surely there's an accurate way to measure forces without creating such a huge known force?! Nope. This appears to be the best way, with a stack of 20 x 50,000 lb masses creating a maximum force of 4.45 MN or 1,000,000 pounds of force. I also wouldn't have thought about all the corrections that need applying - for example buoyancy subtracts about 125 pounds from the weight of the stack. Plus the local gravitational field strength must be taken into account. And, the gravitational field varies below grade. All of this must be taken into account in order to limit uncertainty to just five parts per million (.0005%)

itishappy 2y ago

Skill issue.

gangorgasm 2y ago

What is "Mpc"., if anybody knows?

613style 2y ago
megaparsec (1 million parsecs)
- gangorgasm 2y ago
  Thanks much
tyfon 2y ago
It is a distance unit, megaparsecs. Or approximately 3.25 million light years.
- gangorgasm 2y ago
  Appreciated. Big distance I have difficulty conceptualizing "distance over time ... over [huge] distance" I guess it means "chunks about so [megaparsecs] large are moving [themselves] at a speed of so many Km. per second" but I could be wrong
  - tyfon 2y ago
    The measurement for expansion is linear with distance, so two spots one Mpc from another moves away front each other at 67.4 km/s while two spots two Mpcs from each other moves at 134.8km/s. This means the expansion is accelerating and some parts of the now visible universe will eventually move away from us faster than the speed of light resulting in them disappearing from our view. The distances, time and speeds are indeed very hard to comprehend from our usual references :)
    - gangorgasm 2y ago
      It's crazy that some parts of the universe will actually for all purposes vanish Thanks for taking time to break it all down

halayli 2y ago

Reading your very confident response it makes me wonder the same about you.