Recent comments in /f/askscience

DrMaxwellEdison t1_jb34z1i wrote

Reply to comment by Aseyhe in Does the age of the universe depends on where you are? by _bidooflr_

A follow up question, if I may.

Is there some consensus on a more precise age for the universe than "13.7 billion"? Certainly it's not something that matters in the context of our own life spans, but at some point that 13.7 has to go up. Like the joke of a guard working in a museum who says a dinosaur is 65 million and 4 years old, because it was 65 million when they started working there 4 years ago.

So, is there some agreed-upon starting point we can count up from?

1

sciencedthatshit t1_jb332xy wrote

Reply to comment by sth128 in What happens at the end of a subduction zone? When the entire plate subducts? by kittens0423

If that civilization was on the ocean floor, sure.

The "what if geological processes erased a truely ancient civilization" question comes up frequently and the most rigorous treatment of this thought experiment is contained in a paper called The Silurian Hypothesis...check out the wikipedia article on it and the paper as well if you're interested in that sort of thing.

290

CJW-YALK t1_jb32dyc wrote

Reply to comment by Indemnity4 in Why does sand keep clay from shrinking as it dries? by UnderBridg

Unrelated: but on the subject of micro-scale clay particles…kaolin is a iron deficient white clay, relatively high in alumina…it’s used for all kinds of products. One use is paper, those same “hands” over lap each other and provide a smooth surface….if you’ve ever thought “man this paper is nice to write on” vs something like a napkin, your writing on the over lapped kaolin particles….(napkins, toilet paper etc are mostly tree fiber and absorb) …..heavy heavy application of kaolin can provide the slick feel of magizine at the extreme end, though many of them have moved to polymers

So next time your writing a note on nice smooth paper, remember your actually writing on dirt

43

Anonymous_Otters t1_jb313dn wrote

Reply to comment by JasonDJ in Does the age of the universe depends on where you are? by _bidooflr_

Atomic clocks are routinely used to measure the time difference between things on the surface of earth and things in orbit. The difference of the flow of time needs to be calibrated or else things like GPS wouldn't work right.

If communication were instant, how it would work would I guess depend on what you were using, since that isn't supposed to be possible.

16

Grimyak t1_jb30k5j wrote

Reply to comment by criminally_inane in Does the age of the universe depends on where you are? by _bidooflr_

From a technical standpoint, every location has its own distinct area of influence, even if they have points that overlap each other. However, this doesn't contradict my earlier point as far as I can tell.

To illustrate this concept, imagine three circles that overlap in a linear fashion. The outer two circles extend inward, but do not touch. While an outer circle can interact with the portion of the inner circle that it overlaps with, the inner circle cannot transmit this information beyond the point where it is overlapped by the outer circle. Essentially, although each circle has the potential to overlap with another's influence, it is still unable to communicate or affect regions outside of its own radius.

1

JasonDJ t1_jb30ffx wrote

Reply to comment by Anonymous_Otters in Does the age of the universe depends on where you are? by _bidooflr_

So, wait a tick…

If you’ve got two watches in perfect sync on earth, and one leaves at a low rate of speed (well below speed of light), where is “out” of our gravity well that they are significantly losing sync, and would that still hold true with atomic clocks?

Assuming we had some sort of hypothetical instantaneous radio communication, would the communications be distorted once one side were in a different gravity well?

6

Indemnity4 t1_jb2zqez wrote

Reply to Why does sand keep clay from shrinking as it dries? by UnderBridg

Same idea as bricks and mortar for building a house - the bricks are the structural support and the mortar is the fluid stuff holding the bricks together.

Same idea as adding grog to your clay.

Microscale, clay particles shaped like little flat overlapping discs. Place your hands over each other and then imagine 10 people all overlapping hands to do a big Lets Go Team! cheer. They are also charged like magnets. The water in the clay is phsycially separating the clay particles so they can slide over each other and be worked.

When you are working the clay it is wet and all the little charged discs are pushing each other away. However, when you are drying the clay (biscuit phase) or firing, the water evaporates. All those little charged discs start to be attracted to each other and pull together.

Some types of clay have what's called a "vitreous component" or a "flux" - it's just naturally in the type of clay, although it can be an additive too. It's stuff inside the clay that melts during firing and turns into glass. Sounds great, but the solid->liquid phase change is smaller volume so it makes little bubbles inside the clay wall.

Overall, the clay shrinks and pressure starts to build up in the walls.

The grog or sand is an inert piece of material that slow down shrinkage and reduces internal pressure in the clay structure.

Now, with this grog additive, during firing some of the clay melts to form a fluid glass that moves to fill in the voids between the solid grog. Other clay melts to fill that hole, and so on. You end up with a much stronger piece of clay with less shrinkage and much less likely to shatter to relieve that internal pressure.

133