**Ask a monkey a physics question thread**

[MadMojoMonkey]

Pretty sure pressure has no effect on density unless the material is a gas or plasma. Pressure is just the force acting on a material. [/layman]

This is generally a fine approximation.

It's hard to convince yourself that when you squeeze a doorknob, you're changing its shape, but the physics says it's so.

[Renton]

Too lazy to read 4 pages of this thread to see if it's addressed, sorry.

I feel like states of matter are relatively arbitrary. I was taught in high school chemistry that glass is technically a liquid that flows unbelievably slowly, and that this could be observed in old houses, where the panes of glass are somewhat thicker at the bottom than at the top, due to creep. Is every solid somewhat amorphous like this, or is there some sort of boundary where a solid is truly solid and a liquid or amorphous solid is something different? I would imagine that diamond is a solid in the purest sense of the word, so does it have something to do with having a crystalline structure? I know from a liquid to a gas there's a clear difference because gases can be compressed to change volume and liquids cannot. I'll stop babbling.

[OngBonga]

Thanks mojo! This thread is awesome.

[MadMojoMonkey]

I feel like states of matter are relatively arbitrary. I was taught in high school chemistry that glass is technically a liquid that flows unbelievably slowly, and that this could be observed in old houses, where the panes of glass are somewhat thicker at the bottom than at the top, due to creep.

I heard that before, too, but I don't think it's actually true.

Nope.

unlike the molecules in conventional liquids, the atoms in glasses are all held together tightly by strong chemical bonds. It is as if the glass were one giant molecule.

From: The 'glass is a liquid' myth has finally been destroyed

Is every solid somewhat amorphous like this, or is there some sort of boundary where a solid is truly solid and a liquid or amorphous solid is something different?

I think this is answered above. Let me know or restate it if not.

I would imagine that diamond is a solid in the purest sense of the word, so does it have something to do with having a crystalline structure?

A crystalline structure is definitely not a liquid, as the spacing and arrangement of the atoms defines the crystal. This is another "like a giant molecule" case, but it's really not, since the bonds are quite different

That feels iffy... I'm soft on chemistry, ultimately. (Is Chemist here?)

I know from a liquid to a gas there's a clear difference because gases can be compressed to change volume and liquids cannot.

It's all about the fact that in a gas there are no inter-molecular bonds because the kinetic energy of particle collisions is greater than the bonding energy.

In a liquid, there are weak inter-molecular bonds. In a solid, there are strong inter-molecular bonds.

Since the particles in a gas aren't bound together, they're not "touching", and there is space between them. So by compressing the volume, you're reducing the space between particles.

In liquids and solids, the atoms/molecules are bound to their neighbors already, so in order to compress them, you have to squish them closer together than they are. Quantum Mechanics has some stuff to say about that, and the reaction force rises rapidly with slight distortions.

I'll stop babbling.

How dare you, sir!

[MadMojoMonkey]

This post is about pressure in a gas. It is not about liquid pressure; the particles in a liquid are already touching, and the collisions are minimal.

I always assumed pressure was the collective weight of what's above you, so water pressure is the weight of all the water directly above you, plus 1 atmosphere of air pressure.

Pressure is not weight. Pressure is force applied over an area. Weight is a force.[/nitpicking]

As far as the pressure you experience while walking around and swimming, that's right.

If you were in a sealed chamber, though, the pressure can be anything, regardless of the pressure outside the chamber. So long as the chamber is constructed to withstand the pressure differential.

If it's particle density, well that explains why pressure increases with temperature, and it explains atmpospheric pressure because gas is compressible.

I think you've gone off track a bit here.

Pressure increases with temperature because temperature is a way of talking about the vibrations of particles. Ultimately, temperature is just a measure of kinetic energy. When temperature increases, the particles vibrate more vigorously. When the more vigorously vibrating particles bounce off of each other, they impart more energy to each other, and increase the average velocity of the particles. This increased velocity means that the collisions are more forceful.

The increase in pressure associated with temperature increase is due to higher average particle speeds. The higher speed particles bounce off of the walls of their vessel with greater force because they're moving faster. This increased force per bounce results in greater pressure.

If pressure has no effect on the density of a liquid, then how does particle density increase? That's why I'm confused, because I agree with what you said renton and that doesn't tally with the idea that pressure is simply a measure of particle density.

Pressure is a relationship between number of particles, the volume in which they are contained, and the temperature of those particles.

This is because a consequence of increased temperature is increased average particle speed.

When the particle density goes up, the pressure goes up because there are more particles bouncing around.

When the temperature goes up, the pressure goes up because the particles are bouncing harder.

[OngBonga]

Pressure is not weight. Pressure is force applied over an area. Weight is a force.[/nitpicking]

I think this nitpicking actually helps to explain my confusion better than anything else you've said!

When you said pressure is increased particle density, I foolishly assumed that is what ALL pressure was ultimately caused by on a quantum level. Then I started to think, how does particle density increase at the depths of an incompressible medium such as a sea?

Thanks for the explanation.

[OngBonga]

I now understand that weight causes pressure, as does temperature, as does anything else that applies a force. Is this correct?

[MadMojoMonkey]

Thanks mojo! This thread is awesome.

Thanks for the explanation.

You're welcome.

It's as good for me as it is for you.

I got my degree and have never worked as a physicist, so I'm years rusty. This helps me refresh that info.

I love to answer the questions. I am always disappointed when I see the thread go for a few weeks with nothing new.

There are so many tangents I can spin off on to when I'm composing a post that I often wonder how you guys let me get away with so much meandering just to barely tie it back in at the end. I feel like I'm throwing bread crumbs everywhere, just to see what you guys want to follow.

[OngBonga]

I never studied phsyics or chemistry in any detail at school, which is a huge shame because it interests me so much. So my understanding of physics is pretty much thanks to intuition and internet, which means it's heavily flawed and limited. But I'd still bet it's a better grasp than most uneducated folk. I would love to study phsyics properly.

[MadMojoMonkey]

I now understand that weight causes pressure, as does temperature, as does anything else that applies a force. Is this correct?

Yes, I think you have it. There are more ways to describe pressure (e.g. particle density may be a factor), but everything you said jives well with me.

***
Now let me mess with your head.

Hydraulic Pressure (what we've been discussing) is a statistical averaging of a huge number of miniscule forces over an area.

Hydraulic pressure is mostly electromagnetic repulsion of the electrons in the outermost shells of atoms and molecules. (It is also the resistance to bending of the inter-molecular bonds - still electromagnetism.) From a "distance" an atom has neutral charge because it has an equal number of protons in the nucleus and electrons in the electron shells. Since protons and electrons have equal and opposite charges, they cancel out, with a net charge of 0. However, "up close" the electrons are on the outside, shielding the positive charge on the inside. This means that the electrons of one atom are close to the electrons of the other atom... and they repel, as like charges do, by expressing the Coulomb Force on each other.

The Coulomb force is the electromagnetic force that says, "Like charges repel. Unlike charges attract. Here's how much."
It is stylistically no different from Newton's Law of Gravitation.

Spoiler: Show

Newton:
F = -GMm/r^2

Gravitational force, F, equals Newton's Gravitational Constant, G, times the mass of one body, M, times the mass of the other body, m, divided by the square of the distance between them, r^2. The minus sign tells us that like "mass-charges" attract, and unlike "mass-charges" repel. Since all mass has positive "mass-charge", the force is always attractive. (There is no observation of negative mass.)

Coulomb:
F = {pink elephant} Qq/r^2

Electromagnetic force, F, equals {pink elephant} times the charge of one particle, Q, times the charge of the other particle, q, divided by the square of the distance between them, r^2. The lack of minus sign means that like charges repel, and unlike charges attract.

{pink elephant} = 1/(4*pi*{ongbonga})

where {ongbonga} is the electrical permittivity of free space, usually {epsilon_0}

There are stronger forces, which can result in pressures under "exotic" conditions.

***
Totally different kinds of pressure (but still the result of QM forces on particles):

When a massive star begins fusing Iron, its core will collapse, and it will supernova. This is because Iron takes more energy to fuse than it gives off in having fused. It is the lightest element to have this property. Once the star begins to fuse Iron, the pressure in the center goes up and it fuses Iron faster, which makes the pressure go up... it's the chain reaction that is the death-knell of the star.

(A star had to die for there to be Iron to make blood. *mind blown every time*)

How does a thing which has stopped pushing outward against the gravitational force suddenly explode against that force?

The core collapses, falling to the center. eventually the electrons are pressed so close together that QM basically just says "No." This is the electron degeneracy pressure. The electrons are facing the limit of particle density described by the Pauli Exclusion Principle. The PEP says that no 2 fermions can be in the same state at the same time. Electrons are fermions. When the core collapses, all of the particles rush to the center of the star, which quickly fills up. Once those electrons are at maximum particle density, then you have something which makes "incompressible water" look like a sponge.

That electron degeneracy pressure is so great that the in-falling star bounces off of it at nearly the speed of light. Supernova

BUT, that's not the "hardest" pressure.

If the star is big enough to leave a stellar remnant, The result could be as "exotic" as a neutron star.

In a neutron star, the electron degeneracy pressure was overwhelmed. The PEP would not yield, and so the electrons could no longer exist in the same volume and the increased pressure of the in-falling star forced the electrons to bond with the protons into neutrons.

A neutron star has the greatest mass-density of anything that is not a black hole. The entire object is almost wholly composed of neutrons, with only a small percentage of protons and electrons that are unbound. The pressure is too great for the electrons and protons to separate and form atoms in any notable amount.

[MadMojoMonkey]

I would love to study phsyics properly.

When you have the time:
1) Pick a course
2) Watch the first lecture(s).
3) Bring me your questions.

It's really that easy.

If you're interested in physics, there's a few MIT courses that are on youtube. Dr. Walter Lewin is an amazing professor and every lecture has a demonstration to show you what he's describing. These lectures were an essential companion to my own education during freshman year.

For classical mechanics:
Lec 1 | 8.01 Physics I: Classical Mechanics, Fall 1999

For Electricity and Magnetism:
Lec 1 | MIT 8.02 Electricity and Magnetism, Spring 2002

For Vibrations and Waves (an essential primer if you wish to understand Quantum Mechanics):
Lec 1 | MIT 8.03 Vibrations and Waves, Fall 2004


EDIT: I can just about promise you that this will not be boring. However, my own bias is clear. I think Dr. Lewin presents things in such a way as to bring fascination to the student, and even students who once thought physics was boring come away with a real appreciation of how much fun it can be.

[OngBonga]

(A star had to die for there to be Iron to make blood. *mind blown every time*)

Yup mind blown here too!

Cheers for the list of lectures, i'll look into those soon.

[MadMojoMonkey]

I re-watched the first couple lectures of the 8.01 course. I have to warn you that no matter how exciting I claimed it is, it's still a physics lecture... and not very exciting, really. I'd wager that if you're not studying what he's saying it's downright boring.


I forgot how much time you have to spend going over vectors in order to just get started in physics. If you want my advice for the first thing to learn if you want to get into physics, I'd say learn about vectors.

Learn the difference between vectors and scalars.
Learn vector addition.
Learn how to determine the magnitude of a vector.
Learn about dot product and cross product. (There are 2 ways to multiply vectors.)

Then brush up on the most basic of trig. I.e. SOH/CAH/TOA

***
Once you understand that much, then we can start drawing Free Body Diagrams (FBD). An FBD is a simplified picture that allows you to label and visualize the significant forces involved in a scenario, as an aid to writing down correct equations.

***
Then you need to learn the implications of Newton's Laws of Motion, since that's where we'll be getting our first equations.

1) A reference frame that is accelerating is no good.
2) F = ma / Force equals mass times acceleration
3) F_AB = -F_BA / If object A expresses a force on object B, then object B expresses and equal force, applied in an opposite direction, on A.

[chemist]

I never studied phsyics or chemistry in any detail at school, which is a huge shame because it interests me so much. So my understanding of physics is pretty much thanks to intuition and internet, which means it's heavily flawed and limited. But I'd still bet it's a better grasp than most uneducated folk. I would love to study phsyics properly.

You didn't miss anything at school.
Nelkon & Parker was the standard A-Level textbook.
https://archive.org/details/AdvancedLevelPhysics
Read it and yawn. The joys of calculating angular momentums without any practical reason.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

I feel like states of matter are relatively arbitrary. I was taught in high school chemistry that glass is technically a liquid that flows unbelievably slowly, and that this could be observed in old houses, where the panes of glass are somewhat thicker at the bottom than at the top, due to creep.

That feels iffy... I'm soft on chemistry.

Actually it is pure physics. Viscosity at room temperature.
In the American Journal of Physics, materials engineer Edgar D. Zanotto predicted the relaxation time for Germanium Dioxide at room temperature would be 10 to the power of 32 years, (that's a few billion and a few more zeros), which is quite a bit longer than our universe has been around.
Silicon Dioxide Glass is an even thicker liquid so would flow even slower at standard Ts and Ps. The old house would have to be in another much older universe to observe any creep.

What's the difference between an amorphous solid and a non-Newtonian fluid?
Is this why ketchup doesn't come out of the bottle?
If you bang it too hard would the bottle flow as well?
Could the ketchup and bottle form a colloidal suspension?
Is Renton correct that states of matter can appear relatively arbitrary?

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

The Coulomb force ... is stylistically no different from Newton's Law of Gravitation.

We like the electrical permittivity of free space.

[MadMojoMonkey]

TL;DR
Wowee! That's a long time.

***
10^32 years is unimaginably longer than a billion years (which is already fairly unimaginable).

10^9 is a billion. If you multiply a billion times a billion, you get 10^18. A billion billions is still (much) less than one billionth of 10^32.
If you multiply that billion billion by a billion, you get 10^27, which is still 1/10,000 of 10^32.
A billion billion billions is still 0.01% of 10^32.

Even if he meant 10^32 seconds, that is still 3*10^24 years... which is still more than a billion billion years by a factor of 100,000.

Here's a sense of how long away that really is. I hesitate to cite this, but it illustrates what I was thinking about how long that time scale is. It's just that these predictions are heavily motivated by hypotheses, and widely speculative.

10^19 - 10^20 [years from now]: Estimated time until 90% – 99% of brown dwarfs and stellar remnants are ejected from galaxies. When two objects pass close enough to each other, they exchange orbital energy, with lower-mass objects tending to gain energy. Through repeated encounters, the lower-mass objects can gain enough energy in this manner to be ejected from their galaxy. This process eventually causes the galaxy to eject the majority of its brown dwarfs and stellar remnants.

10^30 [years from now]: Estimated time until those stars not ejected from galaxies (1% – 10%) fall into their galaxies' central supermassive black holes. By this point, with binary stars having fallen into each other, and planets into their stars, via emission of gravitational radiation, only solitary objects (stellar remnants, brown dwarfs, ejected planets, black holes) will remain in the universe.

Wikipedia "Timeline of the far future"

***
Relaxation time is a measure of exponential decay. Which means that the amount of relaxation that occurs during the relaxation time is proportionally the same amount of relaxation that always occurs over that time period. It's like radioactive half-life or the charging time of a capacitor. I bring this up because even after the relaxation time has passed, that only implies some percentage of the total relaxation having occurred, not full relaxation.

***

We like the electrical permittivity of free space.

Of course we do. It's awesome. If you're reading this, and you are on the fence about the electrical permittivity of free space, then go ahead and say, "electrical permittivity of free space" and see how you feel about it then.

OR

Chemist wants to cuddle, too, Ongie.

[MadMojoMonkey]

What's the difference between an amorphous solid and a non-Newtonian fluid?

You're throwing me softballs, now.

Proof Non-Newtonian fluids are awesome.
This is not in English, but it doesn't matter. They have a decent sized pool of (I'm guessing) oobleck, or cornstarch and water.
Skip to 1:30 for the part where 1 person is submerged in the pool while another is running on the surface.

Making oobleck is a great way to kill an hour with any age group who hasn't played with it before.
I mean ANY age group - from toddlers up to "Am I dead yet?"

I'll talk about the physics in another post.

Is this why ketchup doesn't come out of the bottle?

Ketchup is a normal, Newtonian, viscous fluid.

Viscosity is "resistance to flow" and ketchup has it. It also has surface tension which tends to hold the surface of the fluid in place.
When you try to pour an old-fashioned glass ketchup bottle, especially if it's new, and full, with a smaller surface area, then the viscosity and surface tension teem up to restrict the flow of the ketchup in the small gap.

If you turn the bottle so point downwards and shake it, you have another problem. The whole mass of ketchup wants to move out the opening, but in so attempting, it creates a vacuum pressure behind it, which prevents it from flowing. The viscosity is thick enough to prevent "glugging" for a surface area that small.

If you lay the bottle sideways and give it a gentle back-and-forth wiggle, you can get the surface tension to break, and the ketchup will start to flow. Alternatively, you could just use a knife or any pokey-tool to mark the smooth surface of the ketchup in the bottle, and it would then flow.

If you bang it too hard would the bottle flow as well?
Could the ketchup and bottle form a colloidal suspension?

I think those are possible only if you bang it hard enough to pulverize the glass into sand, but I fear you're trying to trick me.

Is Renton correct that states of matter can appear relatively arbitrary?

Absolutely. There is gray area in this, and Renton is only talking about the 4 most common states of matter. We've not discussed super-critical fluids, or the super-fluid state of Helium, or the semi-fluid behavior of sand.

Atoms bond to each other in some blend of ionic and covalent bonding. It's never purely one or the other. Molecules bond many atoms together, with various strengths of ionic/covalent at each bond. It is the nature of the inter-atomic and inter-molecular bonds that determines the characteristics of a substance, along with temp., pressure, density.

[chemist]

You're throwing me softballs, now.
Absolutely. There is gray area in this,

They were of course rhetorical questions to illustrate some of the grey areas.
I threw ketchup in as a familiar example of a shear thinning fluid.
Where shear stress {bleh}={blah}*({ong}/{bong})

[OngBonga]

You have no idea how much it pleases my ego to see ong and bong form important parts of equations.

[OngBonga]

Why is the value that mass and energy are relative to one another related to the speed of light? This is not a coincidence, surely? Does it not imply that not only are matter and energy different aspects of the same thing, but also different aspects of space and time too?

[OngBonga]

If that doesn't make any sense, maybe it's clearer to ask... why c squared?

[MadMojoMonkey]

Why is the value that mass and energy are relative to one another related to the speed of light?

Damn, that's a good one.

After a couple hours of searching, that's not an easy question to answer. The closest I have now is an explanation of the fact that Einstein took 11 more years to work out GR once he worked out Special Relativity. It wasn't a single flash of insight that he fully understood all at once. It was slowly developed on the back of experimental data showing that the speed of light is constant in all directions, regardless of the speed of the observer. It was developed in the knowledge that light is an electromagnetic wave, which obeys Maxwell's Laws. The speed of light can be derived from Maxwell's Laws and 2 measured values:

1) The electrical permittivity of free space, ε_0
2) The magnetic permeability of free space, μ_0

such that c = 1/SQRT(ε_0*μ_0)


The motivation for Einstein's Relativity was that the previous hypothesis said that space was not "empty", but made of "aether". This hypothesis implies that the speed of light would be like any other speed: If you are moving in the same direction of a moving object, then that object's speed relative to you appears less than it would appear to a stationary observer. (This is known as Galilean Relativity today, but was the only relativity theory at the time.) However, many experiments, culminating in the Michelson-Morley Experiment were collecting data which showed that the speed of light is the same in all directions, regardless of the speed of the observer.

The Earth is spinning on its axis, as well as orbiting the sun, so the "actual" speed of a single spot on Earth's surface varies between night and day, and with the seasons. No matter where on Earth or when the experiment was performed, the speed of light was always the same. Experiments on Earth measuring the speed of light always show the same value, regardless of whether it's day or night, or summer or winter.

The motivation behind Einstein's Theory was to explain observations about light, so the speed of light being an integral part seems obvious.

This is not a coincidence, surely?

It's not a coincidence, and stop calling me Shirley.

Does it [...] imply that not only are matter and energy different aspects of the same thing, but also different aspects of space and time too?

I think so. Mass/energy warps space-time, so they're intrinsically linked in an inter-active way. As I understand it, there is no other source of space-time warping.

If that's true, then all of these descriptions are equivalent. Mass = energy = warp in space-time.

If that doesn't make any sense, maybe it's clearer to ask... why c squared?

Great question, ong!

This may take some time. Everything I've read seems so excited that E = mc^2, that it's not too concerned about where the c^2 came from.

***
Interesting side note: E = mc^2 has very little to do with fission physics. The popular link between E = mc^2 and atomic bombs is erroneous. Fission reactions result in almost no conversion of mass into energy. The energy comes from the breaking of inter-nuclear bonds, not mass-to-energy conversion.

Mostly what we observe in this mass-energy equivalence is the very tiny change in mass of a substance when it absorbs or emits photons... or changes temperature.

[Renton]

So wait, a photon traveling head on with another photon is only going at a rate of c from the perspective of the other photon? What the fuck?

[MadMojoMonkey]

So wait, a photon traveling head on with another photon is only going at a rate of c from the perspective of the other photon? What the fuck?

Anything moving at the speed of light experiences infinite time dilation. That means that clocks don't tick.

Anything moving at the speed of light experiences infinite space contraction in the direction of travel. This means that there is no space in front of them or behind them.

I posit that nothing moves from the perspective of a photon.

One photon that is "in front of" another photon, "traveling head on" is in fact, counter-intuitively, in the same place, at a different time.
...
or something equally weird

***
I give a more rigorous response to your question:

If two light particles are on a direct colliding course, are they relatively (to each other) moving at 2x the speed of light?

Here in post #65

[Renton]

ROFL, my brain sucks.

[Renton]

I feel kind of like what we perceive as space time is like a 2d plane and massless particles are infinitesimal tips of a cones that pierce our plane from some higher dimension.

Or at least, that's the kind of shit I was seeing last time I robo-tripped.

[OngBonga]

Anything moving at the speed of light experiences infinite space contraction in the direction of travel. This means that there is no space in front of them or behind them.

So do this imply that from the photon's frame of reference, the universe is disc with a thickness the same as the photon? That there is space perpendicular to its direction of travel? I assumed that from the photon's pov, it sees the universe as a singularity.

[MadMojoMonkey]

@Renton: No worries about needing a refresher on this stuff. It's so against intuition that I'd think less of anyone who just accepts it as fact w/o question. I respect a sense of skepticism when someone tells you something that is at odds with what you observe. This is the core of science, after all.

I def. agree that what we are able to directly perceive as space-time with our human senses is incomplete.

@ong: I don't think I can do better than post #65, honestly. I focused on QM instead of GR, and I never took a class devoted to GR, so all I know is introductory stuff.

[OngBonga]

No worries. I think it's a thought experiment at best anyway, I mean who the hell can experimentally confirm how a photon views the universe?

I think GR interests me more than QM if I'm honest. I've been watching some particle physics lectures by Michel van Biezen on youtube and once we get to lectons and isospin all that stuff it just fries my brain. I have a hard enough time trying to figure out what the hell the weak and strong forces are. But gravity, I feel like I can follow along with GR without my head melting.

[MadMojoMonkey]

I think GR interests me more than QM if I'm honest. I've been watching some particle physics lectures by Michel van Biezen on youtube and once we get to lectons and isospin all that stuff it just fries my brain. I have a hard enough time trying to figure out what the hell the weak and strong forces are. But gravity, I feel like I can follow along with GR without my head melting.

Thanks for the name drop on Michel van Biezen... I'm looking at his youtube page now. I haven't clicked a vid yet, but it looks like it's right up my alley.

***
Leptons are a class of fundamental particles with isospin 1/2.

This means they are Fermions. Fermions have non-integer isospin (1/2, 3/2, 5/2, etc). Bosons have integer isospin (1, 2, 3, etc). Everything (Yes, all the things) is either a fermion, a boson or composed of fermions and/or bosons.

The important thing to know about isospin is that it is an intrinsic property of a particle. I usually talk about isospin by just calling it spin, or spin-state, but it's something you're probably familiar with.

E.g. In every electron shell, there can be up to 2 electrons. All Fermions follow the Pauli Exclusion Principle (PEP). The PEP says that no 2 fermions can be in the same state at the same time. What's going on, here?

An electron can be either in an 'up' spin state (isospin +1/2) or a 'down' spin state (isospin -1/2). So the spin state is fundamentally important to describe the energy of an electron bound in an atom.

Ultimately, the word spin is misleading, since there is no classical spinning going on. It's just a number that is attached to the particle, like the mass is just a number that's attached to the particle... or the electric charge. As such, calling it isospin is slightly less misleading.

***
The weak force is electromagnetism and also the facilitating mechanism behind "low-energy" atomic changes.
In general, the weak force is what describes electrons' behavior.

The strong force is interactions between quarks, and is the dominant force holding atomic nuclei together.
In general, the strong force describes protons' and neutrons' behavior.

***
I know that it's boring to study F = ma to death, but it's important that you understand the applications and implications intuitively. The higher concepts are all built on simple ideas. It's like you're trying to jump into the story in the middle of act 2 and you're a bit confuzzled over the characters and plot direction.

[chemist]

If that doesn't make any sense, maybe it's clearer to ask... why c squared?

Spooky, I was asking myself the same thing yesterday.
I was thinking effective energy equals mass times some {ongbonga} speed constant squared.
On earth it is acceleration or gravity F=MA, where A is speed squared.

But why C?
Because Einstein assumed that Energy always travels at the speed of light as a light wave or some other form of radiation. And Squared because Acceleration is speed squared.


Newton F=MA, Einstein E=MC^2
My Universal Equation D=dM*dS^2
Where D is Dimensional Energy, dM is dimensional mass and dS is dimensional speed.

[chemist]

Interesting side note: E = mc^2 has very little to do with fission physics. The popular link between E = mc^2 and atomic bombs is erroneous. Fission reactions result in almost no conversion of mass into energy. The energy comes from the breaking of inter-nuclear bonds, not mass-to-energy conversion.

The reason Einstein's equation is important to atomic bombs or nuclear power funnily enough is the C, because the resulting energy releases at the speed of light.

Which makes the energy a very big number
if c=299792458 m/s
then c^2 = 8.98755179×10^16
So a small mass can make a lot of energy.

[MadMojoMonkey]

I was thinking effective energy equals mass times some {ongbonga} speed constant squared.
On earth it is acceleration or gravity F=MA, where A is speed squared.

There is nothing special about the Earth in terms of physics. F = ma is true everywhere (everywhere we've looked, at least).

A is acceleration. Acceleration is the derivative of speed with respect to time, or the 2nd derivative of position w.r.t. time.

Acceleration is not speed squared. Dimensional analysis shows the units of acceleration are { L/T^2 }, while the units of speed squared are { L^2/T^2 }.

Furthermore, you're equating force to energy, and they are different things. Energy is (in one form) force applied over a distance.
Kinetic energy is mass times one-half times velocity squared.

But why C?
Because Einstein assumed that Energy always travels at the speed of light as a light wave or some other form of radiation.

I can look into this.

And Squared because Acceleration is speed squared.

Still no.

Speed is the first derivative of position w.r.t. time.
v = dx/dt

Acceleration is the 2nd derivative of position w.r.t. time.
a = dv/dt = d^2x/dt^2

Jerk is the monkey who points this out twice, while jerk is also the 3rd derivative of position w.r.t. time.

Newton F=MA, Einstein E=MC^2
My Universal Equation D=dM*dS^2
Where D is Dimensional Energy, dM is dimensional mass and dS is dimensional speed.

I'm thinking your Universal Equation is suspiciously equivalent to Newton's equation for Kinetic Energy.

Newton KE = M(V^2)/2, Einstein E^2 = M^2 C^4 + P^2 C^2

Part of the beauty of Einstein's equation is that it explains the energy of a massless photon as E = pc while also describing the intrinsic mass of a stationary (resting) particle as E = mc^2. It also predicted the change in mass associated with temperature change.

EDIT: I can't believe I forgot the factor of (1/2) in the Kinetic Energy.

[MadMojoMonkey]

The reason Einstein's equation is important to atomic bombs or nuclear power funnily enough is the C, because the resulting energy releases at the speed of light.

Which makes the energy a very big number
if c=299792458 m/s
then c^2 = 8.98755179×10^16
So a small mass can make a lot of energy.

"Somehow the popular notion took hold long ago that Einstein's theory of relativity, in particular his famous equation E = mc2, plays some essential role in the theory of fission. Albert Einstein had a part in alerting the United States government to the possibility of building an atomic bomb, but his theory of relativity is not required in discussing fission. The theory of fission is what physicists call a non-relativistic theory, meaning that relativistic effects are too small to affect the dynamics of the fission process significantly."
-Robert Serber of the Manhattan Project

"While Serber's view of the strict lack of need to use mass–energy equivalence in designing the atomic bomb is correct, it does not take into account the pivotal role which this relationship played in making the fundamental leap to the initial hypothesis that large atoms were energetically allowed to split into approximately equal parts (before this energy was in fact measured)."

-Wiki

[chemist]

Well spotted I had conveniently ignored that speed is measured in m/s and acceleration is measured in m/s^2 not (m/s)^2.
And indeed I was thinking more about Kinetic Energy than Force.

EDIT: I can't believe I forgot the factor of (1/2) in the Kinetic Energy.

But didn't Albert do the same thing.
Why isn't it E=M(C^2)/2

I haven't seen: E^2 = M^2 C^4 + P^2 C^2 before,
that takes the wind out of next weeks questions on electro magnetic radio waves where I was going to say albert was wrong because E=0*C^2 would equal zero for a massless photon.

But start doing your research because I still have some humdingers on radio waves.

[MadMojoMonkey]

Why isn't it E=M(C^2)/2

This is by far the best response I've found.

I've been struggling for a way to say it without invoking so much calculus, but I don't think it's possible.

There's just not a conclusive way to answer this in layman's terms.

***

I was going to say albert was wrong because [...]

I admire that bravado. I mean, you're doomed, chem, but running into it headlong like that... bold move, sir.

[MadMojoMonkey]

Can you vaporize a water droplet by shooting it with a laser? Not really, no.

3 minutes of slow motion shots of shooting a droplet of water with a focused laser pulse.

[JKDS]

For humans trying to achieve flight, why hasnt the "big bird wings, and flap em really fast" approach worked? With enough physics and the proper bird wings, why cant I literally "make like a bird" and fly over to my friend's house?

If we're too heavy, bigger wings and an engine to flap them? Pterodactyls flew though, and they were big...

****
http://xkcd.com/435/ For levity, how does this make you feel?

*****

A Mososaurous weighing 20tons (evenly distributed, lets say) and measuring 17m in length lives in a lake at a theme park. He swims into the audience viewing area, jumps halfway out of the pool to feed, and then falls back into the water.

Not unlike this: https://www.youtube.com/watch?v=Zv8qID-89ts

How big a splash/wave would the mososaurous have caused? (Height, distance traveled, and tons of water maybe?)

[oskar]

How big a splash/wave would the mososaurous have caused? (Height, distance traveled, and tons of water maybe?)

This is important to me now!

[MadMojoMonkey]

For humans trying to achieve flight, why hasnt the "big bird wings, and flap em really fast" approach worked? With enough physics and the proper bird wings, why cant I literally "make like a bird" and fly over to my friend's house?

If we're too heavy, bigger wings and an engine to flap them? Pterodactyls flew though, and they were big...

Basically, it's more energetically efficient to spin a propeller in a circle, generating a constant thrust, than it is to swing a long, heavy beam back and forth (creating thrust in pulses). However, biologically, there is no such thing as an axle. So biology uses what it can, but it can't make wheels, or propellers, that only spin in one direction and never bind.

Having produced thrust, the same thing hits you with the wings of the plane. If they sit still, no energy is required to flap them back and forth. If they're the right shape, they can generate phenomenal amounts of lift.

An F/A 18 Hornet would need 8 - 10 more engines pointing down to generate as much lift as it gets from its wings. I.e., the up-force a good airfoil can generate is more than 4 times the force needed to keep it moving at a speed where it can generate such forces.

Get yourself one of these:



***
TIL Pterodactylus was about the size of a bald eagle. However, Quetzalcoatlus was a Pterosaur with a 30 - 50 foot wingspan, weighing ~500 lbs.

http://xkcd.com/435/ For levity, how does this make you feel?

This is an old joke / commentary. I don't know any physicist who would question the validity of the sentiment, or any mathematician who isn't at least a tiny bit smug about it. This is all brotherly love, though.

Except there is a dramatic divide between the biologists and the psychologists. Even the move from chemistry to biology is a step away from concrete cause-effect relationships most of the time.

A Mososaurous weighing 20tons (evenly distributed, lets say) and measuring 17m in length lives in a lake at a theme park. He swims into the audience viewing area, jumps halfway out of the pool to feed, and then falls back into the water.

Not unlike this: https://www.youtube.com/watch?v=Zv8qID-89ts

How big a splash/wave would the mososaurous have caused? (Height, distance traveled, and tons of water maybe?)

You guys. Not only is this so hard to put real boundaries on, 2 of you are all excited about it, so I can't as easily blow you off.

First of all, that wasn't half way. At most that was the head and not much neck, but I digress.

The short answer is: There is a huge amount of variability involved. It could be ultra-tiny, or it could be a deluge.

The amount of water displaced is pretty easy to imagine. The amount of volume is the same (or very nearly so), whether it's dinosaur or water.

Everything else is guesswork. The shape of the surface as it goes into the water makes a huge difference. An Olympic diver may leave next to no splash at all in a competition dive. I'm sure that's not the case if you could convince one to do a cannon ball.

If you jump in as though to do a canon ball, but then you thrust your legs forward just as you hit the water, you can send a large splash quite a good distance forward.

The surface tension relationship between the water and the dino's skin is going to make as much impact on splash size as the geometry of how the dino plunges into the water.

(The first few seconds is enough)


Hydrophobic: The surface tension is such that water does not stick to the surface. (a thin coating of oil would do.)
Hydrophilic: The surface tension is such that water sticks to to the surface (like water curles up a little bit at the edges in a glass cup.)

Other factors: surface debris on the water will make a big difference in the way waves propagate. That's why a nice foamy guinness doesn't slosh around and spill at parties. One more reason Guinness is the best.

If you feel like I've blown you off - well, I did. If I can find a way to postulate a maximum splash size, I'll get on it.

[MadMojoMonkey]

This is not all that helpful as pertains to the splash question, but if you ride it through to the end, it's worth the chuckle.

http://www.askamathematician.com/201...-a-dump-in-it/

[acg123]

does our solar system have an end? or a place in space where a ship could not travel any further due to magnetic fields?

if yes, what is inbetween said solar systems? and could we "jump" from one to another?

if no then this is clearly the reason we haven't been enslaved by aliens.

Question 2:
is it possible our planet was "selected" and seeded by us from another "solar system" where our bodies would not survive the travel time, but single cell organisms would as would DNA?

[wufwugy]

Not a monkey, but lots of physicists have had bad answers to these in the past IMO because the answers aren't just from a series of calculations.

if no then this is clearly the reason we haven't been enslaved by aliens.

We haven't been enslaved by aliens because an intra-galactic dominating lifeform would have to be so advanced that it has no incentive to enslave humans. It would have no incentive to even come near Earth. It would likely just be a network of machines that get all energy and material from a small amount of sources: a sun, asteroids, or even just quantum factories (probably quantum factories)

The other reason is that the sheer magnitude of spacetime and energy needs combined with the relative youth of all possible life determines that there just aren't any intra-galactic empires possible

Question 2:
is it possible our planet was "selected" and seeded by us from another "solar system" where our bodies would not survive the travel time, but single cell organisms would as would DNA?

I think it is technically possible, but in order to get past the magnitude of the task, the aliens would have to basically be God. You don't hit a bullseye across a galaxy. And even if you could, you don't want to. When you're that advanced, you don't think it's a good idea to spread obsolete seed to a potential host candidate that will arrive in like a hundred thousand years

[MadMojoMonkey]

does our solar system have an end?

Many. Here's 2:

Gravitational boundary:
There's the region of space which is 'downhill' toward the sun, or the solar system's gravity well. Inside this boundary, things fall toward the sun. Outside this boundary things fall away from the sun, and toward whatever the dominant gravitational object is in that region.


Much inside the gravitational boundary is the Heliosphere, a region of space which is plainly and obviously full of stuff that came from the sun:
This makes a tear drop shape solar system boundary, since particles moving away from the sun still slow down, but are less likely to fall back.






Make special note of the scale on the 2nd image. Alpha Centauri is the closest neighbor star to the sun. On this logarithmic scale, 1/3 of the distance from the sun to Alpha Centauri is just about where the 10^5 is.

To be clear, these are artists' representations using colors to signify regions. Space is not colored like that (unfortunately).

or a place in space where a ship could not travel any further due to magnetic fields?

No.
Magnetic fields, like gravitational fields, get weaker as you move away. The 'boundaries' of the solar system aren't a 'wall', more like a hilltop. On top of the hill, a ball will roll in any direction. Once it's down the hill a little way, it rolls down the hill in a certain direction.

The boundaries of the solar system are where there are 'no' forces, or more accurately, where all the forces are balanced.

if yes, what is inbetween said solar systems?

Um... it's no, and the answer is very little.

When I say very little, you probably think you understand my meaning. I think you probably don't.

A "perfect" vacuum in the best laboratory on earth is still ~ 1 billion times as dense as a nebula. Astronomers call a nebula a "dense cloud". Are you starting to sense the scale here?

A "perfect" vacuum here on earth is still a billion times as dense as a nebula. A nebula is ~ a billion times more dense than empty space.

When I say there is very little there. I mean there's miles and miles and miles between atoms.

I fear I'm understating my case.

and could we "jump" from one to another?

That depends on what you mean by 'jump'.

In the far future, if humans survive long enough to do so, travel between the solar systems in our galaxy may become a reality. Travel between galaxies is laughable, though. It's another jump in scale that human brains have trouble dealing with.

if no then this is clearly the reason we haven't been enslaved by aliens.

You should never trust anyone who goes from "I don't know" to "It must be" with no steps in between.

Question 2:

We should agree on a counting system at some point.

is it possible our planet was "selected" and seeded by us from another "solar system" where our bodies would not survive the travel time, but single cell organisms would as would DNA?

This hypothesis is called Panspermia.

There is evidence that some bacteria and microbes survive the vacuum and radiation levels of space.

[MadMojoMonkey]

Not a monkey, but lots of physicists have had bad answers to these in the past IMO because the answers aren't just from a series of calculations.

Physicists like good, solid predictions. We don't care about calculations except when they help to predict a result. If a cartoon provides an accurate prediction, we'll use a cartoon.

Math is a tool of physics, not the goal. We didn't choose the tool, we use every god damn fucking thing that we can fashion into a tool and nudge physics to see if it helps. When the nudging stops working, we beat at physics with it anyway for years and years (I'm looking at you, string hypothesists).

Eventually we look for something else that helps.

Many, many, ... , many physics students wish that math wasn't a part of it at all.

We haven't been enslaved by aliens because an intra-galactic dominating lifeform would have to be so advanced that it has no incentive to enslave humans. It would have no incentive to even come near Earth. It would likely just be a network of machines that get all energy and material from a small amount of sources: a sun, asteroids, or even just quantum factories (probably quantum factories)

The other reason is that the sheer magnitude of spacetime and energy needs combined with the relative youth of all possible life determines that there just aren't any intra-galactic empires possible

... so you're saying you think we HAVEN'T been enslaved by aliens?



How shall we test this hypothesis?

I think it is technically possible, but in order to get past the magnitude of the task, the aliens would have to basically be God. You don't hit a bullseye across a galaxy. And even if you could, you don't want to. When you're that advanced, you don't think it's a good idea to spread obsolete seed to a potential host candidate that will arrive in like a hundred thousand years

This actually makes some interesting points.

If you weren't interested in time scales or targeting any particular planet, you could certainly send out your interstellar jiz missiles en masse.
(Pardon my French)

[wufwugy]

Physicists like good, solid predictions. We don't care about calculations except when they help to predict a result. If a cartoon provides an accurate prediction, we'll use a cartoon.

Math is a tool of physics, not the goal. We didn't choose the tool, we use every god damn fucking thing that we can fashion into a tool and nudge physics to see if it helps. When the nudging stops working, we beat at physics with it anyway for years and years (I'm looking at you, string hypothesists).

Eventually we look for something else that helps.

Many, many, ... , many physics students wish that math wasn't a part of it at all.

I just find myself scratching my head at concepts like Fermi Paradox. I don't think it's a paradox at all yet it appears to be one if there are only a handful of considerations.

... so you're saying you think we HAVEN'T been enslaved by aliens?



How shall we test this hypothesis?

I think we test it by defining it and collecting data. If we can't distinguish between enslavement and freedom, then we have not defined it. If we can distinguish them, then we can figure the data accordingly.

I feel like doing so would give ample evidence that we are not enslaved by aliens. This isn't to say that we're not a part of some unknown greater mechanic, but that's not the same as being enslaved by aliens. Even something as strange as our thoughts being their energy should be testable. But even then it's not testable as long as the definition is to test an unknown

This actually makes some interesting points.

If you weren't interested in time scales or targeting any particular planet, you could certainly send out your interstellar jiz missiles en masse.
(Pardon my French)

If humans used every bit of raw material the solar system has to offer, sending out trilions of vessels, wouldn't that be virtually nothing in the scope of the galaxy? We'd just be spreading seed to empty space

[MadMojoMonkey]

I just find myself scratching my head at concepts like Fermi Paradox. I don't think it's a paradox at all yet it appears to be one if there are only a handful of considerations.

It seems like a very strong conclusion based on highly speculative and incomplete information.

FWIW the wikipedia page has dozens of responses to why the Fermi Paradox is what it is. Most of them sound like a bunch of wild speculation but some of them seem to be based on reasonable assumptions.

The bottom line is that we have nearly 0 data on answering the questions that outline the parameters of this.

I think we test it by defining it and collecting data. If we can't distinguish between enslavement and freedom, then we have not defined it. If we can distinguish them, then we can figure the data accordingly.

I feel like doing so would give ample evidence that we are not enslaved by aliens. This isn't to say that we're not a part of some unknown greater mechanic, but that's not the same as being enslaved by aliens. Even something as strange as our thoughts being their energy should be testable. But even then it's not testable as long as the definition is to test an unknown

SMH
and you call yourself a soul reader

If humans used every bit of raw material the solar system has to offer, sending out trilions of vessels, wouldn't that be virtually nothing in the scope of the galaxy? We'd just be spreading seed to empty space

Well, I kind of meant targeting a star that is likely to have a 'good' planet and shooting at it a bunch of times. However, the odds of hitting the planet and not the star are gonna take some tweaking. If you had some automatic controls and not just a rock with some cells on it, then it wouldn't take too much.

I think the important thing is that "life support" systems may be unnecessary for a long-term project. This makes the cost of sending life out to 'seed' the galaxy much lower.

The motivation to do such a thing is beyond me, but that doesn't mean that no intelligence would see a motivation.

[wufwugy]

alien virtual reality would be far superior to actual reality. aint nobody sending out no seeds

[MadMojoMonkey]

alien virtual reality would be far superior to actual reality. aint nobody sending out no seeds

This sounds like another case of "i don't know" to "It must be" with no steps in between.

You may be right about the notion of seeding life, as far as the scale of the galaxy and the relatively miniscule amount of matter in the solar system by comparison.

The thing about the Panspermia hypothesis is that it doesn't require intelligence. Unintelligent life may be distributed by natural means.

The other thing is that the probability of a successful seeding is non-zero. Even the first opportunistic attempt could be successful, no matter how unlikely that is.

It is well worth noting that humans have observed only the tiniest bit of the universe, and that questions which seem like paradoxes are common in this stage of observation. Think of all the "paradoxes" surrounding QM and GR. Schroedinger's cat, the Twin Paradox, etc. None of them is truly a paradox, they just present information in a misleading way, and that presentation implies false assumptions.

In time, the Fermi Paradox will likely be revealed to be no paradox at all (based on the observation that all explained physical paradoxes have all been shown to be false). Unfortunately, that time scale could be millions of years.

[MadMojoMonkey]

is it possible our planet was "selected" and seeded by us from another "solar system" where our bodies would not survive the travel time, but single cell organisms would as would DNA?

Is it possible? Speaking purely hypothetically, yes, it is possible - or at least conceivable.

***
DNA is an essential molecule, known to all forms of life. Living cells also contain carbohydrates and proteins. DNA is not enough on its own.

A selectively permeable cell wall is fundamentally important, as well - I think. (I'm not a biologist.)

***
The difficult part is that the evolutionary end-game is ridiculously unpredictable. Look at the vast variety of life on Earth from animals, plants, fungi, insects... all of them evolved from a single cell over billions of years.

For a sense of scale as pertains to time: 1 billion seconds is ~31.5 years. One billion years is an inconceivable amount of time compared to a human life-span.

***
So I'm saying the notion of Panspermia is not too unreasonable. The notion of some intelligent creature trying to recreate themselves via this method seems absurd. (I could be an ignorant monkey, who does not understand what that species understood about evolution.)

[Renton]

I've watched a bunch of Lewin vids per your recommendation ITT. After like 8 lectures, I'm spellbound by this guy. Then I find out he's a pariah at MIT because of sexual harassment. I dunno if its just the men's right activist / cynic in me coming out but this guy's character seems unindictable to me. I tried looking up the details of the scandal and they don't seem to exist on the internet. Do you know anything about it?

(sorry not a physics question)

[MadMojoMonkey]

This is the first I've heard of it.

I found this:
http://tech.mit.edu/V134/N60/walterlewin.html

and this:
https://newsoffice.mit.edu/2014/lewi...s-removed-1208

and an article from the Boston Globe.


This seems to be for real. MIT isn't saying there are allegations, they're saying they have reviewed the case and they agree with the accusations.

There are no details, but I expect it's legit if MIT made an official announcement and then pulled online content.


EDIT: These articles are dated Dec. 8, just a week and a half ago.

[Renton]

Meh man given what rad-fem cesspools higher education circles in America have become, I think I need more than an official MIT statement to be convinced.

[MadMojoMonkey]

The articles read like it was all email-based, and that the women who were sexually harassed were college students (adults).

I'm not jumping the gun to call an 82 year-old man a sexual predator over this stuff. When it comes to this kind of behavior, I stand by these words of wisdom:
Once an asshole, always an asshole.

If this guy is a predator, there should be 60 years of paw-prints that come to light in very short order.

***
Richard Feynman candidly shared that in his private life, men were basically invisible to him, he only noticed women. He was the kind of guy who liked to lie on the beach sipping a cocktail and smiling like a creep at the young women in bikinis. He was open and shameless about his view of women.

By today's standards, that guy would not be allowed anywhere near a college classroom. His contributions to physics would not even be discussed in the modern news world. All we'd get is a byline about a creep who wrote a paper that no one took seriously for decades.

[wufwugy]

Recommend me a Lewin video

This sounds like another case of "i don't know" to "It must be" with no steps in between.

It's dismal science stuff, for sure. Not experimental science stuff. Ofc all sciences are experimental, just some are near impossible for us to run experiments on

Anyways, my point is that if we compile everything we understand about physics and biology and everything, I think we will find it would be very peculiar and perhaps entirely impossible for there to exist an alien species with strong galactic expansion behavior

It is well worth noting that humans have observed only the tiniest bit of the universe, and that questions which seem like paradoxes are common in this stage of observation. Think of all the "paradoxes" surrounding QM and GR. Schroedinger's cat, the Twin Paradox, etc. None of them is truly a paradox, they just present information in a misleading way, and that presentation implies false assumptions.

In time, the Fermi Paradox will likely be revealed to be no paradox at all (based on the observation that all explained physical paradoxes have all been shown to be false). Unfortunately, that time scale could be millions of years.

Ah that makes more sense now. Granted, I thought Schroedinger's cat and Twin Paradox are called paradoxes because they are legitimately sound paradoxes where new information changes nothing. What I understand about Schroedinger's isn't that we don't have enough information to know the state of the cat, but that we can't have enough information to know the state of the cat. Whereas Fermi's seems simply to be a question with poor assumptions and the answer comes with new information.

I would find it strange today to hear physicists give much credence to Fermi's. Relative to scale, the galaxy isn't teeming with life (and never could), and there are a million other reasons why advanced life wouldn't/couldn't expand beyond their solar systems.


RE: Panspermia. If Occam's Razor was ever needed, it's here. The probability of a planet creating its own life is probably immeasurably higher than it being brought by an asteroid created from a different star.

[MadMojoMonkey]

1st off: Schroedinger's Cat is BS. It is a pathetically flawed attempt to provide a macroscopic example of a microscopic phenomenon. Also, it is needlessly murderous of a cat.
It attempts to illustrate probability driven behavior (in this case nuclear decay), by making that probabilistically driven thing act as a gate switch. It could have been expressed much more simply and without the cat.... but it made good press, so... yeah.

The idea is that we prepared an atom that has a 50% chance to decay in some half-life and sealed it in a box. If we wait that time period (the half-life), then even though we had perfect knowledge of what was in the box at the start of the experiment, we now can not state with absolute certainty what is in the box. The answer to what is in the box can only be expressed probabilistically without opening the box and observing the atom.

It fails to describe a superposition of states, which is what he was attempting to explain. In QM, some measurable properties, like a particles energy, are described by probability waves. This is true even for identically prepared systems of particles. The end-result of the system after time has passed will be based on probabilities, and is not strictly predictable.

Prior to QM, it was the general belief of learned people worldwide that a thing was where it was and it is moving how it is moving, that the energy of a thing is definite, and predictable. QM was in the process of tearing down those notions, and Erwin Schroedinger was not the best at narrative tales.

***
The twin paradox is called a twin paradox because the 2 people start the experiment with identical age, but end the experiment with different ages. This is considered a paradox because it implies that time flows the same for all things. It is experimentally observed that this is not a paradox because time does not pass at the same rate for all things.

***
Even our solar system could not support life if it was not so isolated from other stuff in the galaxy. The amount of life-killing radiation that is being spewed around and out of planetary nebulae is really a deal breaker for a bacterial colony on a planet there. Supernovae don't have to be "nearby" to wash a planetary system with gamma rays that ionize every atom they touch. Nearby stars can fling outer planets out of their orbits and bombard the inner planets with asteroids in cycles that last many thousands of years.

It's hard to evolve complex life when the slate gets wiped clean so often.

[a500lbgorilla]

On the Size of Black Holes

[MadMojoMonkey]

Yeah. I giggled to myself at the end when it kept booming and booming to get to 20 billion.

It's hard to show just how many of a thing a billion is.

Even though this is a pretty good attempt, it's still awe-inspiring at best, and doesn't give you an actual feel for the immensity of the scales involved.

I mean... Crush the sun down to the size of Manhattan? Oh, hey, yeah, my brain's totally equipped to handle that kind of thing.

Stop and think about this for a second. The amount of mass in the solar system that is sol itself is 99.87%

Here are some pie charts I made comparing the masses of the planets to that of the sun.



The chart on the top right is the same as the chart on the bottom left, essentially.

See just how much mass the sun has compared to Earth.

[wufwugy]

yet still nothing compared to the mass of my biceps

[OngBonga]

Jupiter is pacman. That's the answer to the meaning of life.

[MadMojoMonkey]

Jupiter's awesome. The Hydrogen atmosphere is so dense that it conducts like a metal.

Nothing is known about Jupiter's core. The metallic Hydrogen atmosphere obscures all electromagnetic waves that might be going into or coming out of it. It is assumed that there is a rocky core, implying some surface to the planet, but it is entirely speculative. The extreme gravitational pull makes sending a probe in to record data, then come back out to relay the data laughable. If we could make a probe that withstood the pressure, that is.

[OngBonga]

I always wondered if you could, in theory, travel through Jupiter. I guess the ultimate conclusion I reach is that the immense pressures means the idea of a gas in the conventional sense is redundant, that even if it's technically a gas, it's going to behave like a solid. We can turn a gas into a liquid and keep it like that using a thin layer of metal to contain the pressure. I can't even begin to imagine what the gravity and pressure forces inside Jupiter can do.

[Renton]

The observable universe's mass has a Schwarzschild radius of approximately 13.7 billion light years.

Is this just a random coincidence that its approximately the age of the universe or does this mean we're all in a black hole? :/

[OngBonga]

Apparently, there are more potential chess positions than there are atoms in the known universe.

Fuuuuuuuck.

[wufwugy]

Apparently, there are more potential chess positions than there are atoms in the known universe.

Fuuuuuuuck.

i do not understand how they are calculating this.

if i learned the correct thing in chemistry, a mol of h20 is tiny (18 grams?) yet contains 6.022x10^23 molecules. it doesn't take that many mols for this number to be bigger than 10^81

[OngBonga]

Well according to a quick search there's 10^120 different possible chess positions, compared to 10^79 atoms in the universe. I have no idea how they calculate the latter.

[MadMojoMonkey]

Is this just a random coincidence that its approximately the age of the universe or does this mean we're all in a black hole? :/

Not according to Sean Carrol. He says it's a consequence of spacetime being spacially flat.

I think this calculation is based on only observable matter in the observable universe. That means that it doesn't account for dark matter or dark energy, or the fact that the observable universe is not widely believed to be the whole universe, due to cosmic inflation.

[MadMojoMonkey]

i do not understand how they are calculating this.

if i learned the correct thing in chemistry, a mol of h20 is tiny (18 grams?) yet contains 6.022x10^23 molecules. it doesn't take that many mols for this number to be bigger than 10^81

lolwat.

10^81 / 10^23 = 10^(81 - 23) = 10^58 grams

water is 1 gram per cc.

1000 cc/L means 10^55 Liters of water. Divide that down to m^3, which means divide by another million.
(1 L is 10 cm on a side, 1 m is 1000 cm on a side. which means each side increases by a factor of 100, and 100^3 is 1 million)

So now that's 10^49 m^3 of water. :/ Lets go to (km)^3. So we'll divide by a billion.

10^40 (km)^3 of water is a lot of water.

The all the water on Earth is ~1.3(10)^9 (km)^3.

So 10^81 water molecules is, ya know, like enough water for 10 thousand billion billion billion Earths.

[wufwugy]

lolwat.

10^81 / 10^23 = 10^(81 - 23) = 10^58 grams

water is 1 gram per cc.

1000 cc/L means 10^55 Liters of water. Divide that down to m^3, which means divide by another million.
(1 L is 10 cm on a side, 1 m is 1000 cm on a side. which means each side increases by a factor of 100, and 100^3 is 1 million)

So now that's 10^49 m^3 of water. :/ Lets go to (km)^3. So we'll divide by a billion.

10^40 (km)^3 of water is a lot of water.

The all the water on Earth is ~1.3(10)^9 (km)^3.

So 10^81 water molecules is, ya know, like enough water for 10 thousand billion billion billion Earths.

first unit is molecules, not grams

the claim, as far as i understand it, is that 18 grams of water is equivalent to 1 mole of water, which is equivalent to 6.022x10^23 molecules of water. if that's true, it does not take that many molecules to swiftly blow past 10^81. im not saying the consensus number is wrong, but i dont understand why it's right

according to calculations i was taught in chemistry, there are approximately 3.343x10^22 molecules of h2o in 1 gram of h2o. not to mention that's of a molecule with 3 moles of atoms

please tell me what im doing wrong here

[OngBonga]

The difference between 10^23 and 10^81 is truly immense.

Like, one followed by nearly sixty zeros immense.

[OngBonga]

Just to give you an idea of how immense 10^81 is, it's 12 times bigger than 10^23 CUBED, so it's 12*(10^23)*(10^23)*(10^23).

Bigger than your ego wuf, and yes, even bigger than my dick.

[OngBonga]

In fact it's even bigger than that. Much bigger. My brain is melting just trying to figure out how to calculate the relative sizes, let alone trying to envisage the number itself.

[wufwugy]

Bigger than your ego wuf

bigger only because my ego is a black hole

[wufwugy]

i really hope you guys figured out the ego thing is a joke by now

i act like im tough shit but im really not

[OngBonga]

The fact there's 10^120 potential chess positions is... I don't fucking know what it is. What comes after mind boggling?

[wufwugy]

i guess i cant comprehend the exponential

apparently atoms in the sun is just 10^57, which just seems so low if there are 10^23 molecules in less than an ounce of water