Planck Time Problem: Calculation & Explanation

AI Thread Summary
The discussion revolves around understanding Planck time, a fundamental concept in physics that signifies the earliest moments of the universe. Participants are trying to find a combination of three constants—speed of light (c), gravitational constant (G), and Planck's constant (h)—to derive a time measurement. One user attempts to combine G and h but initially ends up with incorrect units, indicating a need for further calculation to isolate seconds. The conversation highlights the confusion faced by beginners in physics, particularly in applying fundamental constants to derive meaningful results. Clarification and guidance on the correct approach to the problem are sought.
Sagari
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Homework Statement



Hi Guys,
Just started a Mechanical Engineering Course and in my Physics this came up, I'm really confused and don't know were to start. I was wondering if anyone could shed any light on the subject. Thanks guys.

Three of the fundamental constants of physics are the speed of light, c = 3.0 × 10⁸ m/s, the universal gravitational constant, G = 6.7 × 10ˉ¹¹m³·kgˉ¹·sˉ², and Planck’s constant,
h = 66 × 10ˉ³⁴kg·m²·sˉ¹.
Find a combination of these three constants that has the dimensions of time. The time is called Planck time and represents the age of the universe before which the laws of physics as presently understood cannot be applied.
Using the formula for the Planck time derived in part (a), what is the time in seconds?

Homework Equations



The Attempt at a Solution

 
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Sagari said:

Homework Statement



Hi Guys,
Just started a Mechanical Engineering Course and in my Physics this came up, I'm really confused and don't know were to start. I was wondering if anyone could shed any light on the subject. Thanks guys.

Three of the fundamental constants of physics are the speed of light, c = 3.0 × 10⁸ m/s, the universal gravitational constant, G = 6.7 × 10ˉ¹¹m³·kgˉ¹·sˉ², and Planck’s constant,
h = 66 × 10ˉ³⁴kg·m²·sˉ¹.
Find a combination of these three constants that has the dimensions of time. The time is called Planck time and represents the age of the universe before which the laws of physics as presently understood cannot be applied.
Using the formula for the Planck time derived in part (a), what is the time in seconds?

Homework Equations



The Attempt at a Solution


If you multiply G by h, the units are (m³·kgˉ¹·sˉ²) x (kg·m²·sˉ¹)

this gives

kg0·m5·sˉ3

which isn't seconds, but at least the kg has gone!

Use the right amount of the quantities and you will be left with just seconds, presumably.

EDIT: there was no real reason why I chose G and H to start with - but I had to chose a couple of them to show what happens.
 
PeterO said:
If you multiply G by h, the units are (m³·kgˉ¹·sˉ²) x (kg·m²·sˉ¹)

this gives

kg0·m5·sˉ3

which isn't seconds, but at least the kg has gone!

Use the right amount of the quantities and you will be left with just seconds, presumably.

EDIT: there was no real reason why I chose G and H to start with - but I had to chose a couple of them to show what happens.

Ok mate thanks for the help
 

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