Timespan for Stormlight Archives? (Spoilers)

[Sir_Read-a-Lot]

Incidentally, I found this quote, from when Taravangian is telling Szeth about the death-messages.

"We do not know why dome speak when others do not,"  Taravangian said.  "But the dying see something.  It began seven years ago, about the time when King Gavilar was investigating the Shattered Plains for the first time."

[cromptj]

On the subject of dates, Brandon has mention that gravity is weaker on Roshar which suggests that it is smaller than the Earth and rotates more slowly. Of course, it could be bigger and made of lighter elements.

[Tortellini]

I'm sorry, how does rotational speed impact gravity? Unless you're rotating fast enough to lessen gravity (like flinging people off the planet )... Rotating more slowly makes no sense

[cromptj]

It needs to rotate more slowly because the day would be too short otherwise. The comment was more about the size of Roshar rather than anything to do with its gravity.

[Cheese Ninja]

Roshar rotates a bit faster than Earth.

20 hours per day, and their hour is like a minute or two shorter than our hour.

The earth's rotation isn't constant, its speed decreases very slowly over time, due to the moon's influence. http://en.wikipedia.org/wiki/Tidal_acceleration

This geological record is consistent with these conditions 620 million years ago: the day was 21.9±0.4 hours, and there were 13.1±0.1 synodic months/year and 400±7 solar days/year.

[cromptj]

That is assuming that it is the same size as the Earth

[Cheese Ninja]

It doesn't matter if it's the same size, bigger, or smaller than Earth.  If it takes 20 hours to rotate, then it has a 20 hour day.

Let's use Mars and Mercury as examples:
Mars has a 24.6229 hour day and is only has 11% of Earth's mass.  Mercury has a 1407.5 hour day and has about the same mass as Mars.  Mercury has nearly the same density of Earth.  Mar's radius is 0.533 Earths, and Mercury's radius is 0.3829 Earths.

The mass only matters for gravity.

[happyman]

It doesn't matter if it's the same size, bigger, or smaller than Earth.  If it takes 20 hours to rotate, then it has a 20 hour day.

Let's use Mars and Mercury as examples:
Mars has a 24.6229 hour day and is only has 11% of Earth's mass.  Mercury has a 1407.5 hour day and has about the same mass as Mars.  Mercury has nearly the same density of Earth.  Mar's radius is 0.533 Earths, and Mercury's radius is 0.3829 Earths.

The mass only matters for gravity.

This is exactly correct, barring some extraordinarily small effects from General Relativity.

Gravity depends only on mass, and the length of the day depends only on how rapidly the planet is turning.  The two can be changed quite independent of each other.  In fact, even black holes have these two parameters independent.

[Tortellini]

It doesn't matter if it's the same size, bigger, or smaller than Earth.  If it takes 20 hours to rotate, then it has a 20 hour day.

Let's use Mars and Mercury as examples:
Mars has a 24.6229 hour day and is only has 11% of Earth's mass.  Mercury has a 1407.5 hour day and has about the same mass as Mars.  Mercury has nearly the same density of Earth.  Mar's radius is 0.533 Earths, and Mercury's radius is 0.3829 Earths.

The mass only matters for gravity.

Actually, Mars has twice the mass of Mercury. Yet at the same time, they both have almost the same surface gravity! Density of the planet also plays a role and can have significant impacts apparently. Source of all my apparent smartness: http://en.wikipedia.org/wiki/List_of_gravitationally_rounded_objects_of_the_Solar_System

The things I learn on this forum... 

[Cheese Ninja]

I used wikipedia too, but I just kept jumping between Mars and Mercury's pages, so I'm not too surprised I screwed something up.