Recent comments in /f/askscience

ArmoredHeart t1_j6asntd wrote

Reply to comment by im_not_u_im_cat in can gemstones be melted into a gradient? by Acceptable_Shift_247

Small-time jeweler and gem dealer also here. I’d like to qualify that hardness of a stone only refers to resistance to abrasion (scratching), and is distinct from tenacity, the resistance to breakage and deformation. Diamond, for instance, has perfect cleavage (planes of weakness in the crystal) in 4 directions (like the top of a pyramid) so, despite its extreme hardness, it’s actually vulnerable to breakage relative to sapphire, which isn’t as hard. To be clear, it still has good tenacity, just not excellent tenacity.

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LittleCreepy_ t1_j6aor09 wrote

Reply to comment by RigbyRoadIce in can gemstones be melted into a gradient? by Acceptable_Shift_247

One stone beginning thin where the other will be thick and slowly reversing that until we get to a single material. Could work if both gems are really clear?

Probably better than my idea of cutting the high temperature gem into a halve band and encasing it in the lower melting one. Then you only have to cut a ring from that stone. I dont know if you can make a gradient that way tho.

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CubanHermes OP t1_j6ak5ph wrote

Reply to comment by slashdave in Is there an upper limit to structure size in a vacuum? Could a sufficiently advanced civilisation build a galaxy sized structure in space or would it become too massive and collapse in on itself? by CubanHermes

>Galaxies are not dense on average, because of the space between stars.

I get that, hence the question as to whether it is theoretically possible to build a structure the size of a galaxy with the space filled in by 'structure' without it collapsing in on itself. It's a hypothetical question so sourcing materials isn't the object of the question; the point is whether, despite the fact it would take several billion years to build at current space traversal times, it would be possible with our current understanding of our universe.

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Ausoge t1_j6ajakm wrote

Reply to comment by Beginning_Cat_4972 in What does it actually mean to “burn fat” during exercise? by orange-robin

I think the reason people talk about the body using up all its carbs before starting to munch on fat reserves is that sugar is the "fast" energy source. It is the easiest energy source for the body to use, because:

  • it requires little to no processing/metabolism/breaking down before its chemical energy can be accessed, as it is a fairly simple molecule.
  • it is stored primarily in the liver and in muscle cells, so it is always immediately accessible during the initial period of exercise.
  • It is water-soluble, so readily dissolves into blood and is easy to transport around the body.

Fats are far more complex molecules than a sugar like glucose. They are made of the same atoms as sugars (C,H,O), so fat can be processed into sugar to replenish depleted reserves, but this requires a level of energy investment before the energy payoff is reached.

For the above reasons, I think it's pretty fair to assume that carbs and sugars will be used preferentially over fats and proteins, simply because of their ease of use and accessibility.

One thing I find really cool about weight loss is how the mass actually leaves the body. I don't remember the exact process, but ultimately it is mostly excreted via your lungs - all that carbon and oxygen is breathed out as carbon dioxide.

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