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H-S-D
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Is it possible to measure the universe' expansion in m/s^2 instead of metres per second per parsec?
Can the Universe's Acceleration be Measured in m/s^2 Instead of m/s/pc?
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In summary, the conversation discusses the concept of measuring the universe's expansion in different units, specifically m/s^2 instead of metres per second per parsec. It is mentioned that one way to express the Hubble growth rate is as a unitless number per unit time, and that attempting to express it as an acceleration would not make sense. The conversation also touches on the similarity between "meter" and "parsec" as units of distance.
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Bystander
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Google "parallax second."H-S-D said:
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marcus
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Hi HSD, Bystander often has good ideas so that may be a good suggestion that you google "parallax second" the root meaning of the distance measure called "parsec", but I do not understand how that relates to your questionH-S-D said:
Maybe I don't understand your question. Of course it is possible to measure the Hubble growth rate in different ways. Parsec is a measure of distance, a unit of length. So the conventional version
eg 67 km/s per Mpc
is a L/T per L quantity and the L units cancel so it is basically a 1/T quantity, a reciprocal time
One way to express the present-day Hubble growth rate H0 is as a unitless number per unit time (a fractional part or percentage per unit time)
like 1/144 percent per million years.
Or as the reciprocal of a long interval of time called the "Hubble time" namely 14.4 billion years.
You can express the Hubble growth rate in various equivalent ways. But you would never express it as a
m/s2 quantity because that would be an ACCELERATION. The growth rate is a fractional growth rate or a speed-to-size ratio. It is not an acceleration! So that would not be mathematically equivalent to the growth rate and would not make sense. What particular distance do you imagine would be accelerating?
So the answer is YES there are a lot of different equivalent ways to express this quantity,
and NO you would not want to try expressing it as a m/s^2 acceleration quantity.
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Two different "seconds."
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marcus
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I see, that makes sense. You suspect HSD of mistakenly imagining that "parsec" is a unit of time, rather than distance.
Could be. There was that famous goof in the Starwars movie.
Anyway, there is a thread (with a poll) about "how do you think of the Hubble growth rate?". Maybe HSD would get something out of it.
I'd be interested in your view, Bystander---what your mental picture of the Hubble rate is, or your concept of it.
https://www.physicsforums.com/threads/poll-how-do-you-think-of-the-hubble-rate.826968/
Could be. There was that famous goof in the Starwars movie.
Anyway, there is a thread (with a poll) about "how do you think of the Hubble growth rate?". Maybe HSD would get something out of it.
I'd be interested in your view, Bystander---what your mental picture of the Hubble rate is, or your concept of it.
https://www.physicsforums.com/threads/poll-how-do-you-think-of-the-hubble-rate.826968/
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George Jones
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Well, if "meter" is a unit of time, so is "parsec" 
.
.FAQ: Can the Universe's Acceleration be Measured in m/s^2 Instead of m/s/pc?
What is the acceleration of the universe?
The acceleration of the universe refers to the increasing rate at which the universe is expanding. It is measured by the cosmic acceleration parameter, which is represented by the letter "q". A positive value of q indicates that the expansion of the universe is accelerating, while a negative value indicates a decelerating expansion.
What is causing the acceleration of the universe?
The exact cause of the acceleration of the universe is still a subject of debate among scientists. However, the leading explanation is the presence of dark energy, a mysterious force that makes up about 70% of the total energy in the universe. Dark energy has a repulsive effect on matter and is thought to be responsible for the accelerating expansion of the universe.
How do we measure the acceleration of the universe?
Scientists use various methods to measure the acceleration of the universe, including studying the brightness of distant supernovae, analyzing the cosmic microwave background radiation, and observing the large-scale structure of the universe. These techniques require precise measurements and complex calculations, but they provide valuable insights into the expansion rate and acceleration of the universe.
Has the acceleration of the universe always been constant?
No, the acceleration of the universe has not always been constant. In fact, scientists believe that the expansion of the universe was initially decelerating due to the gravitational pull of matter. However, about 5 billion years ago, the acceleration began to increase due to the influence of dark energy, and it has been accelerating ever since.
Could the acceleration of the universe eventually lead to a "Big Rip"?
Some theories suggest that the acceleration of the universe could eventually become so strong that it would overcome the gravitational forces holding matter together. This event, known as the "Big Rip," would result in the universe expanding at an infinite rate and eventually tearing apart all matter. However, this scenario is still highly debated, and there is currently no conclusive evidence to support it.