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Physics, Astronomy & Cosmology / Re: How fundamental is time?

« on: 11/01/2019 16:50:14 »

Change and time are not equivalent. Time is a dimension, and change refers to differences within one dimension.

This is most well defined within calculus (sometimes called the math of change), where the symbol ∂ (sometimes d) is used to denote microscopic change, often relating the change of one thing with respect to the change of another.

In this way, we can define instantaneous (microscopic) change of position along a spatial dimension (x) with respect to instantaneous (microscopic) change in time (t) as ∂x/∂t which is equivalent to the velocity in the x direction.

Although time is a very common dimension (variable) to compare changes against, it is not the only one. For instance we can look at the change in altitude with respect to change in forward distance traveled ∂y/∂dx (slope) or the change in cost of making chocolate with respect to the change in the cost of labor ∂$_chocolate/∂$_labor etc. etc.

What I am trying to learn in this thread is whether our concept of velocity (or any other rate of change with respect to apparent time) is best described as a ∂x/∂dt, or if there is a more fundamental variable (I believe I called it α earlier in the thread) such that ∂t/∂α is well-defined, and ∂x/∂α holds up better to the boundary condition that the big bang appears to impose on ∂t.

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Physiology & Medicine / Re: What could cause a too high potassium count?

« on: 09/01/2019 01:51:59 »

Obviously cooking won't make extra potassium appear out of thin air.
I think that cooking just makes the potassium more easily available by breaking down the cell walls.
Or it could be that the reported numbers don't account for loss of water during cooking. I could imagine 100 g of veggies cooking down to 90 g due to evaporated water. Thus 100 g of cooked veggies would have about 11% more potassium than 100 g of raw...

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 16:23:02 »

PS: I think the best definition of time I have ever heard is this (roughly):

"Time is what keeps everything from happening at once"

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 16:22:10 »

Doesn’t the second law of thermodynamics state that in a closed system, entropy tends to increase, or to remain constant.  In spite of the presence of the word “tends”, the assertion “it never decreases” can still be found attached to many explanations.  Could this be a source of confused thinking?  Even in a closed system, can “time progress” in the direction of decreasing entropy?

My understanding is that entropy does not, in fact, determine the arrow of time--it merely demonstrates that there is an arrow.
Entropy is just a natural outcome of statistics. The fact that it is increasing only means that the universe started in a highly ordered state, and is still much more ordered than it ultimately will (can) be.

If we have a small closed system entropy can increase or decrease depending on the initial state.

Imagine four coins that can be either H or T. At regular intervals a coin is selected at random, and flipped such that it has a 50/50 chance of being H or T.

If the system starts out HHHH (the lowest possible entropy for the system), then after the first flip, entropy has a 50% chance of increasing and 50% chance of staying the same. Eventually the system will reach a state of maximal entropy, and can then only decrease or stay the same. Ultimately, as this game continues, the system will oscillate through all possible states with all levels of entropy (with each of the states essentially being favored by entropy).

This scenario is also only valid if the coins are all equivalent, and we don't care about their relationships to each other (you can think of this as the difference between combinations and permutations). If every coin is unique, then all states are equally likely, and have identical entropy. Entropy of the system will never change even though the system clearly changes as the coins are flipped.

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Physics, Astronomy & Cosmology / Re: Does time stand still in the quantum world?

« on: 04/01/2019 08:10:00 »

I think it is very difficult to distinguish between our own personal perceptions of time (which is subjective and based on many complicated and poorly understood biophysical and psychological mechanisms) from the the fundamental temporal dimension that our mathematical models use. Additionally, it is important to remember that even the versions of "time" invoked in our various models is not an accurate representation of whatever "time" "actually" "is"

As far as time standing still in the quantum world... don't be confused by the fact that quantum objects don't appear to follow the same rules as macroscopic objects. The rules are the same (the real world and the quantum world are the same world), we just have to remember that macroscopic objects are collections of vast numbers of elementary particles whose properties are very strongly correlated with each other. This necessarily means that the most important processes and interactions of these enormous collections will be quite different from very small collections of particles.

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Physics, Astronomy & Cosmology / Re: Is there a detectable direction in which the universe is expanding?

« on: 20/12/2018 14:48:47 »

Is there a detectable direction in which the universe is expanding?

Outwards. 

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Chemistry / Re: When would you use d-DMSO over CDCl3 for H NMR?

« on: 25/11/2018 22:00:03 »

Oh, another thing to consider: the residual protiated solvent peak of chloroform shows up at 7.26 ppm, and dmso shows up at 2.5 ppm, so sometimes the choice can be made based on which part of the spectrum you need to look at.

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Chemistry / Re: When would you use d-DMSO over CDCl3 for H NMR?

« on: 25/11/2018 21:57:58 »

DMSO is a much better solvent that chloroform (much more polar and more polarizable than chloroform, and a potent hydrogen bond acceptor to boot)--there aren't many molecular substances that aren't soluble in DMSO, at least enough to get a decent NMR (it's ok for some polymers and some salts as well).

Major disadvantages of DMSO with respect to chloroform: dmso is much less volatile than chloroform (it is very easy to remove chloroform from a sample by distilling it off at low pressure--once dissolved in dmso, there are very few ways to recover a sample), dmso has a very high freezing point (19 °C vs –64 °C for chloroform, so no low-temp VT studies), dmso will absorb moisture from the atmosphere while chloroform will not, substances dissolved in dmso can pass through the skin quite easily, so one must be EXTREMELY careful about handling toxic substances in dmso, and finally, cost (dmso is about 15% more expensive, which isn't crazy, but adds up).

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Chemistry / Re: Why did my radical Tempo arrive in one lump rather than a powder?

« on: 16/10/2018 22:31:12 »

TEMPO is a very stable radical. Don't recrystallize it from hydrogen peroxide or toluene. Do read up on its solubilities and compatibilities. Good luck!

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General Science / Re: Do all things have a start?

« on: 16/10/2018 12:57:08 »

It sounds like what you have said is that everything that is bounded has boundaries, which must be true.

In general, all objects that we interact with are bounded in xyz space and in time.

The universe does not appear to have any bounds in xyz space. As far as I know it is impossible to prove that it actually physically extends to infinity in any direction, but it certainly appears to be effectively infinite, and there is no evidence of any boundary or large-scale curvature, so our best model of the universe now is that it is infinitely large. For any location with coordinates (x,y,z), there is another location 1 m away, with coordinates (x+1,y,z).

I want to revisit your example of the circle though, because I think that there is an interesting point to be made: cartesian coordinates (xyz) are not the only coordinates that have use--and our answer changes if we change our coordinate system. It is often useful to use polar coordinates (especially when dealing with circles), where we can determine any point using the radius from a given point and the angle from a given line that passes through that point. It is easiest to describe a circle in polar coordinates about the point at the center of the circle--for any circle with radius r, any point on that circle can be described by the coordinates (r,θ). And θ is unbounded: for any point (r,θ), there is another point at (r,θ+1).

Ok, so perhaps you wish to claim that this system relies on there being infinitely many repeats of any given point on the circle (what is a unique solution in xy coordinates has infinitely many equivalent rθ coordinates.) That still doesn't preclude the fact that there isn't (for instance) a west-most point on the Earth.

And even if one could use xyz coordinates to bound every object or collection of objects that exist--that doesn't necessarily mean as much as you think it does. For instance: I can define any point in the universe as have a red value between 0 and 1, and can then use that definition to map any object in the universe from its least red point (which it must have) to its most red point (which it must have). In some cases, the object will be completely homogeneous, and only have one red value throughout, and in some cases there will be variation, but we will know that all values will be between the reddest value of 1 and the least red value of 0.

I must go now, but I look forward to responses on this.

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Geology, Palaeontology & Archaeology / Re: What are the principles of stratigraphy?

« on: 03/10/2018 03:21:40 »

I believe there is a mistake in the book, and your understanding is correct: the oldest layers should be the furthest down, and the youngest closer to the surface. (Unless I am also very mistaken)

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General Science / Re: If I wear ANY battery watch, in by a weeks time, the battery is dead. Why?

« on: 23/09/2018 21:47:27 »

Should it make any difference that, if I wear any gold jewelry, my skin turns black and the gold piece starts to get smaller and gain a 'dimpled' surface?

Perhaps people think you are gullible and are routinely ripping you off? High purity gold should not leave a mark on you and won't be corroded by any bodily secretions—you can swallow a small piece of gold (not recommended, other than the gold leaf suspended in beverage such as Goldschlager) and even the acid in your stomach won't do any harm to it whatsoever.

Gold alloys less than 18 karat might leave a dark mark, but shouldn't visibly corrode, but other alloys like brass (which contains no gold), on the other hand can certainly leave dark colored residues on the skin, and could potentially corrode fairly quickly as well.

https://www.fashionlady.in/why-does-your-jewellery-leave-black-and-green-marks-on-the-skin/36450

If you are getting the watches and batteries from the same source that you get your corroding "gold" jewelry, it might be worth looking elsewhere...

If, however, you are certain that you are not getting ripped off, then the fact that you get marks from jewelry lends credence to the notion that your sweat is either more abundant or more corrosive than the typical individual...

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Physics, Astronomy & Cosmology / Re: Why water lifts in very small tubes?

« on: 23/09/2018 05:17:59 »

It's called capillary action and it has to do with surface tension.

https://en.wikipedia.org/wiki/Capillary_action

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Geology, Palaeontology & Archaeology / Re: To what extent can Biblical accounts of Noah's flood be believed?

« on: 20/09/2018 12:48:55 »

None of the stories in the old testament are to be taken as fact. My understanding is that when they were first written (over the course of multiple centuries, by different groups of people http://www.ancient-hebrew.org/articles_authors.html ), no one expected the stories to be taken literally (in fact the bible contradicts itself multiple times--allowing for much more complex analysis by the scholars--and contradicts physical possibility many times as well). Instead the stories are meant to be fables, and only in the centuries after the new testament did it become mainstream to believe that it actually happened exactly as it was written. (possibly due to the philosophical influences of christian and muslim schools of thought.)

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Physiology & Medicine / Re: Is there such thing as emotional violence?

« on: 17/09/2018 21:38:47 »

Emotional abuse is definitely more likely to be a problem in close relationships (as in family, school or work), when it is hard or impossible to avoid interaction, and especially when there is an inherent asymmetry to the relationship (parent-child or boss-underling), but it is definitely possible for a single interaction to be emotionally abusive and devastating.

I would count terrorism as primarily an emotional weapon. Yes, there are often some victims who are physically injured or killed, but the primary target is the psyche of a community. Also threats of physical or social harm can be particularly hurtful even when made by a stranger in passing.

There are ways to protect oneself from emotional attacks, but context is very important, and can change what might be appropriate, so I don't want to just suggest random strategies without knowing more, other than: if it feels harmful, it probably is, but that doesn't necessarily mean that it's malicious (some people are just clueless @$$h0les)

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Chemistry / Re: Why are the half-filled and fully filled orbitals more stable?

« on: 09/09/2018 21:46:54 »

The exchange benefit comes whether the orbital is filled or not.

If all p orbitals are half filled, then there are 3 equivalent electrons (one in each p orbital, and all with the same spin, let's say it's "up"). If all the p orbitals are filled then there are two sets of 3 equivalent electrons (the three "up" electrons can exchange, and the three "down" electrons can exchange.)

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Chemistry / Re: Is there a complete searchable chemical reaction database?

« on: 30/08/2018 23:17:21 »

There are several, but I am not aware of any that is cheap.

scifinder (from ACS) and reaxys (from Elsevier) are the two that I use (payed for by the institution I work at).

These allow for structural input (exact, partial, or similar), and other parameters, such as # of steps, yield, solvent, reagents, etc.

They will bring up any reactions they find in peer-reviewed literature and patents, and provide links to the literature, or links to other related compounds.

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Chemistry / Re: In the compound 'NH₃', why 'N' is in the left?

« on: 29/08/2018 18:31:38 »

If we split 'NH₃', we get 'N³⁻' and 'H³⁺' and in 'NH₃', N is more electronegative than H. So 'H' should be in the left and the formula should be'H₃N' as in 'NaCl' where 'Cl' is more electronegative than 'Na' So could you explain why this structure in 'NH₃'?

It actually splits into N^3– and 3 H⁺, but you're right that the convention for writing chemical formulae often puts the least electronegative element first, like H₂O or HCl. You will occasionally see ammonia written out as H₃N, but NH₃ is more common--probably in analogy to CH₄...

Ultimately it means the same thing whichever way it is written.

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Technology / Re: How do batteries work?

« on: 28/08/2018 02:23:30 »

Essentially any substance can be oxidized or reduced, provided a sufficiently strong oxidizing agent or reducing agent.

Sugar doesn't conduct electricity, so it would be difficult to make an electrode out of sugar, but solutions of sugar can be either oxidized or reduced when exposed to a conductive electrode. The reaction at the other electrode could be reduction of oxygen (an oxygen-sugar "battery" is more properly called a fuel cell), or reduction of silver(I) ions. I know that silver(I) can oxidize sugar because that's how the Tollens test/Tollens reaction works:

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Chemistry / Re: Are there molecules inside the atom?

« on: 12/08/2018 18:39:11 »

molecule + molecule = bigger molecule (if covalently bonded) or adduct (if only bound by intermolecular forces or "dative bonds")