Is M_{Pl} the Planck mass or the reduced Planck mass?

In summary, the value of M_{Pl} used in the Planck (CMB) collaboration's observation papers, such as the one referenced in the link provided, can refer to either the Planck mass or the reduced Planck mass. The reduced Planck mass is defined as 2.176 434 x 10-8 kg according to the NIST webpage, and can be found in the literature with a diagonal line through the letters P or Pl in the subscript. It is recommended to check the specific source for clarification on which value is being used.
  • #1
Alpha2021
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What is the value of M_{Pl} used in the Planck (CMB) collaboration's observation papers, such as the one referenced in this link: https://arxiv.org/pdf/1807.06211.pdf. Specifically, I am wondering if it refers to the Planck mass or the reduced Planck mass?
 
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Thanks for your kind reply.
Definition of reduced Planck mass can be found here.
The problem is that M_{Pl} is used in the literature interchangeably as Planck mass or reduced Planck mass. Did you see anywhere in Planck's papers where they define M_{Pl}?
 
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  • #4
I found in

https://www.cosmos.esa.int/web/planck
> https://www.aanda.org/articles/aa/full_html/2020/09/aa33910-18/aa33910-18.html#S1
1683151818052.png

You may get value of m_pl they use.
 
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  • #6
Alpha2021 said:
What is the value of M_{Pl} used in the Planck (CMB) collaboration's observation papers, such as the one referenced in this link: https://arxiv.org/pdf/1807.06211.pdf. Specifically, I am wondering if it refers to the Planck mass or the reduced Planck mass?
Better practice, although you are right in asking as some authors are sloppy in their typesetting, is to indicate the reduced Planck mass with diagonal line through the letters P or Pl in the subscript, just as one indicates the reduced Planck's constant with a diagonal link through the symbol "h" for Planck's constant.
 

1. What is the difference between the Planck mass and the reduced Planck mass?

The Planck mass (MPl) is a fundamental constant in physics that is derived from the Planck length, Planck time, and Planck constant. It is the mass at which the gravitational force between two objects would be equal to the electromagnetic force between them. The reduced Planck mass (mPl) is simply the Planck mass divided by the square root of 8π. It is often used in theories of quantum gravity and is equivalent to the mass of a particle in a black hole's event horizon.

2. How are the Planck mass and the reduced Planck mass calculated?

The Planck mass is calculated using the Planck length (lPl), Planck time (tPl), and Planck constant (ħ) through the formula MPl = √(ħc/G), where c is the speed of light and G is the gravitational constant. The reduced Planck mass is then calculated by dividing the Planck mass by √(8π).

3. What is the significance of the Planck mass and the reduced Planck mass?

The Planck mass and the reduced Planck mass are important constants in theoretical physics. They are used to study the properties of black holes, quantum gravity, and the early universe. They also play a role in theories that attempt to unify the four fundamental forces of nature.

4. Is the Planck mass or the reduced Planck mass a more accurate measurement?

Both the Planck mass and the reduced Planck mass are accurate measurements, but they are used in different contexts. The Planck mass is used in classical physics, while the reduced Planck mass is used in quantum gravity. Therefore, the more appropriate measurement depends on the specific theory or calculation being used.

5. How does the Planck mass or the reduced Planck mass relate to the Planck energy?

The Planck energy (EPl) is related to the Planck mass through the formula EPl = MPlc2, where c is the speed of light. Similarly, the reduced Planck energy (EPl) is related to the reduced Planck mass through the formula EPl = mPlc2. These energies represent the maximum energy that can exist in the universe according to the laws of quantum mechanics.

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