All Questions
14
questions
-1
votes
1
answer
58
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How exactly did Harrison's chronometer circumvent the impulse problem of time-keeping on a moving ship?
According to folklore, around the time of the exploration of the New World, there was a quandary regarding how to measure time on the open sea. Time keeping then was based on the pendulum clock, which ...
- 179
2
votes
0
answers
79
views
What is Dirac talking about here? [duplicate]
https://www.youtube.com/watch?v=xJzrU38pGWc&ab_channel=mehranshargh
"I might say that my recent work has been very much concerned with Einstein's general relativity and I believe that the ...
- 195
12
votes
6
answers
6k
views
How could Tycho Brahe determine positions without accurate clocks?
Tycho Brahe determined the positions of stars and planets to an accuracy of 2 minutes of angle. Pendulum clocks hadn't been invented yet so he couldn't have known the time to better than 15 minutes. ...
- 165
1
vote
0
answers
87
views
The origin and current status of the equation $\boldsymbol {Et}-\boldsymbol {tE}=\frac{h}{2\pi i}$ [closed]
Heisenberg already in 1927 quotes this equation as a "known equation".[1]
I would like to know that what was the original conception behind this equation, and what is its current status. According to ...
- 745
5
votes
1
answer
645
views
Why was the fraction 1/31,556,925.9747, in the 1956-1968 definition of the second in terms of ephemeris time, chosen?
The recent question Why are leap seconds needed so often? pulled up some interesting details about the definition of the second, and I'd like to have some of them confirmed explicitly.
I'm ...
- 134k
0
votes
1
answer
110
views
Reference for first paper using light clocks
I am trying to find the first historical paper that uses light clocks for special relativity arguments (the famous photon bouncing off mirrors). It seems to me that actually Einstein wasn't the first ...
user78618
1
vote
4
answers
422
views
Why did no one before Einstein realized that time is relative?
If you think about it, it is supposed to be obvious.
It was already proven that the speed of light is constant in all reference frames.
So for the equation $v=x/t$ to be true, when $v$ equals $c $, in ...
1
vote
2
answers
213
views
How measurements for defining a second were made?
As many of you know, the second is defined as
the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the ...
- 113
63
votes
3
answers
27k
views
Why is a second equal to the duration of exactly 9,192,631,770 periods of radiations?
Why is a second equal to the duration of 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom?
Why is the number ...
- 757
3
votes
0
answers
96
views
When did people start to regard "time" as a physical quantity? [closed]
I was trying to figure out how people came to know about time then I realized that people started keeping track of time to know about sunset and sunrise. But I can't figure out how did time came into ...
- 378
9
votes
3
answers
12k
views
Why is the second the SI base unit for time?
Specifically, during the moves towards Le Système international d'unités in the 18th and 19th centuries, why didn't anyone attempt to move us away from the definition of there being 24 hours in a day?
...
- 511
5
votes
1
answer
217
views
If transported back to the 18th century could you solve the Longitude Problem without an accurate clock?
Seeing an interesting BBC article today at http://www.bbc.co.uk/news/science-environment-23514521 about the Longitude Problem, I wondered if it could have been solved, in a way practical at the time (...
- 817
7
votes
5
answers
1k
views
Why a day is divided by 12/24 hours? Why the number 12?
Why a day is divided by 12/24 hours? Why the number 12? Why not using 10 or 6 or 14, 16? Who invented this? Any physical reasons behind this?
- 613
4
votes
3
answers
264
views
How did Cook and other astronomers time the 1769 Venus transit?
The 1769 transit of Venus was observed and coordinated by over one hundred astronomers around the world. How did they measure time so accurately, key to the observations having any scientific value? I ...
- 4,545