I Do we know how many meters long one second is?

  • I
  • Thread starter Thread starter student34
  • Start date Start date
student34
Messages
639
Reaction score
21
TL;DR Summary
Do we know how many meters long one second is?
In other words, how many meters long is the world line of a particle at rest for 1 second?
 
Physics news on Phys.org
student34 said:
Summary:: Do we know how many meters long one second is?

In other words, how many meters long is the world line of a particle at rest for 1 second?
The conversion factor from time to length is the speed of light. For an object at rest in some IRF for proper/coordinate time ##t##, the worldline has length ##ct##.

If ##t = 1s##, then the length of the worldline is approximately ##3 \times 10^{8} \ m##.
 
Possibly illuminating:
 
I guess this means that we pass through time at the speed of light. Interesting.
 
Reply
  • Skeptical
Likes weirdoguy and PeroK
student34 said:
I guess this means that we pass through time at the speed of light.
While there is a sense in which this is true, it is a very limited sense and you can't really draw any useful inferences from it. We have had a number of previous PF threads dealing with the confusion caused by taking this statement too far.
 
Reply
  • Like
  • Informative
Likes PeroK and Keith_McClary

Thread 'I don't see how a black hole's event horizon can be crossed'

OK, so this has bugged me for a while about the equivalence principle and the black hole information paradox. If black holes "evaporate" via Hawking radiation, then they cannot exist forever. So, from my external perspective, watching the person fall in, they slow down, freeze, and redshift to "nothing," but never cross the event horizon. Does the equivalence principle say my perspective is valid? If it does, is it possible that that person really never crossed the event horizon? The...
View full post »

Thread 'Synchronizing clocks in an inertial frame if light is anisotropic'

ASSUMPTIONS 1. Two identical clocks A and B in the same inertial frame are stationary relative to each other a fixed distance L apart. Time passes at the same rate for both. 2. Both clocks are able to send/receive light signals and to write/read the send/receive times into signals. 3. The speed of light is anisotropic. METHOD 1. At time t[A1] and time t[B1], clock A sends a light signal to clock B. The clock B time is unknown to A. 2. Clock B receives the signal from A at time t[B2] and...
View full post »

Thread 'Is the variation of the metric ##\delta g_{\mu\nu}## a tensor?'

From $$0 = \delta(g^{\alpha\mu}g_{\mu\nu}) = g^{\alpha\mu} \delta g_{\mu\nu} + g_{\mu\nu} \delta g^{\alpha\mu}$$ we have $$g^{\alpha\mu} \delta g_{\mu\nu} = -g_{\mu\nu} \delta g^{\alpha\mu} \,\, . $$ Multiply both sides by ##g_{\alpha\beta}## to get $$\delta g_{\beta\nu} = -g_{\alpha\beta} g_{\mu\nu} \delta g^{\alpha\mu} \qquad(*)$$ (This is Dirac's eq. (26.9) in "GTR".) On the other hand, the variation ##\delta g^{\alpha\mu} = \bar{g}^{\alpha\mu} - g^{\alpha\mu}## should be a tensor...
View full post »

Similar threads

I How many meter sticks are there in this length contraction reasoning?
Replies
12
Views
2K
B Calculating Time taken to reach speed with Time Dilation
Replies
18
Views
1K
I How fast does the particle go through spacetime?
Replies
20
Views
2K
B Meaningfulness of the speed of light
Replies
25
Views
2K
I Arguments leading to the speed of light as a dimensionless constant
2
Replies
64
Views
4K
B "Spacetime Physics" by Taylor and Wheeler
Replies
32
Views
5K
I Spacetime expansion - time dimension expansion
Replies
48
Views
3K
I Black Hole: Knock on the horizon
Replies
34
Views
2K
A When and Why Was the Definition of the Meter Changed?
3
Replies
101
Views
11K
I Is the concept of a one-way speed of light meaningful and measurable?
Replies
25
Views
4K

Hot Threads

Recent Insights

Back
Top