ScootysDad t1_j8lnw75 wrote

I'll leave it to someone else to show the math but the short answer is that light is a propagating electromagnetic wave. As it passes through an atom, an electron within feel the force of the light wave and oscillate which sets up its own electric field (albeit at a different frequency). Through superposition, we can than add up the sum of those waves to give a net wave which is slower than the originating light.


ScootysDad t1_j2r15zu wrote

Reply to comment by Aseyhe in How do galaxies move? by modsarebrainstems

That's a yes an no answer mostly because the space between the local clusters are too large. There's a region around the supercluster where objects are gravitationally bound to the center of gravity and outside of that radius the local clusters will eventually escape. Much like the orbital mechanic of our solar system. So from that region outward the dark force appears to dominate and expand the space.

Edit: With our current understanding of the universe, within the Supercluster the dark force responsible for the expansion of the universe is too weak to overcome the gravitational "force" within the bounded section of the supercluster.


ScootysDad t1_j2pq816 wrote

Reply to comment by Krail in How do galaxies move? by modsarebrainstems

Forces have an effective range. At the sub-atomic range, the Strong and Weak forces act on particles like quarks. Above that is is the electromagnetic force which works at the atomic level to the macroscopic level (normal everyday experiences). After that is the gravitational "force" which works at the normal everyday objects like apples, cars, rockets, and people to galaxies, local clusters, and superclusters. All of the above forces are orders of magnitude stronger than the dark force that caused the expansion of the universe.

So, the space between superclusters is vast and gravity no longer hold sways over the space fabric so it stretches.

One posit is that gravity is not a force but rather a time gradient around mass. The closer you are to the central mass the greater the time curvature so the differential time difference causes you to spiral downward through space instead of an actual field that interacts with a particle (like photon to the electromagnetic field or the Higgs boson with the Higgs field to give us mass).


ScootysDad t1_j2oe84f wrote

Yup. Except that there is no expansion of space between our two galaxies. As miniscule as it is, the gravitational "force" is much stronger than the expansionary forces so that rate is 0.

We are in the Laniakea Supercluster and the space between our Supercluster and the next one, Perseus–Pisces Supercluster, are expanding at 73km/s. Within Laniakea, the gravitational "force" keeps us together in the same orbit. Everything is orbiting something.


Edit: 73km/s/megaparsec


ScootysDad t1_j2ockk7 wrote

There's amble evidence that the Milkyway has collided with another galaxy and currently is in the process of incorporating another galaxy into its structure. The other galaxies are drawf galaxies so we maintained out spiral structure. With Andromeda we will not be a spiral any more.

Andromeda is slightly larger and it and 29 other galaxies (including the Milky Way) are part of the Local Group of galaxies. There may have been many more galaxes but they have since been incorporated through glactice mergers. Andromeda and the Milky Way's orbits around our center of gravity will bring about a merger in the distant future. By that I mean one of these galaxies are not in the stable orbit (on galactic time scale). Even after the merger the combined mass and velocity of the the merged galaxies will put us into a different orbit around our center of gravity.

You know what they say: If Andromeda doesn't come to us, we will come to Andromeda.


ScootysDad t1_j2nid7p wrote

This is a trick question. Our current understanding of the universe is this: The portion of the universe that is visible to us is about 93-ish billion light years in diameter or about 28.5 gigaparsecs. Space is expanding at a rate of about 45mi (73km) for every megaparsec. Consequently, beyond the observable universe there are things racing away from earth (frame of reference) faster than light speed thus are part of our particle universe but forever disconnected from our reality. We will never know because any information emitted will never reach us.

I'm hopeful that one day we will devise the necessary physics to dwell into the edges of the universe much like the edges between us and the point of singularity of the black holes.

An interesting thought experiment, as I said earlier, there are things racing away from us at faster than light speed. From their frame of reference, we are receding from them at equal rate. So technically we're both right. We are going through the universe on a roller coaster traveling faster than light. "Make it so"


ScootysDad t1_ixyedl7 wrote

I don't see any new development in material science that can produce a 36,000km cable that an withstand the enormous tension, at least from the popsci environment. Any material science physicists here who can shed some light into this subject matter?


ScootysDad t1_iws6mwh wrote

Remember the hydrogen and helium atoms I mentioned above? These wispery clouds extend up to 400,000 miles into space, gravitationally locked to the earth and formed the geocrorona.

So, yes, no human has ever left the confine of earth's atmosphere.

The actual scientific paper was published in 2019 in the Journal Geophysical Research: Space Physics by Baliukin, Quemerais, & Schmidt.


ScootysDad t1_iwpd8hp wrote

Interestingly, no human has ever left earth's atmosphere. It actually is larger than the moon's orbit around the earth. Atoms like hydrogen and helium are so light that they travel way up there but they are still gravitationally bound to the earth until they collide with another particle (solar wind, interstellar particles) with enough energy that they are ejected. Large solar flares and gamma ray burst can strip the earth of its atmosphere.

Edit: We are running out of helium (important noble gas for cryogenic work) because 7 billion of balloons are being filled each year. 8 now.


ScootysDad t1_ivvp1bu wrote

The BeH2 molecule has a very linear structure with the H atoms bonded "inline" so they cannot be as densely packed as H2O. Further, it's actually a solid and form a kind of crystalline (lots of open space). NH3 (amonia) bonding is something vague for me but I think it has something to do with the electron orbital in O that give is a higher charge than N thus allowing it to be more attractive than N in that configuration. I don't think it comes even close.


ScootysDad t1_ivsvi4c wrote

Surprisingly, water is 14x denser than liquid hydrogen. The bonding angle of the H-O-H makes the O slightly positive and the H slightly negative which then tends to attract another H from the other H-O-H and holds it closer (surface tension). Even at cryogenic level water will have more H than liquid H.


ScootysDad t1_iv05gjr wrote

Any moving electron produces an electric field. In a complex body they tend to cancel each other out so much so that our basic detectors can't detect. The iron in the hemoglobin, the electrical impulses from the nerves, they all produce a magnetic field.