I saw a question in the last week along the lines of “If the universe is 13 billion years old and expands at the speed of light, then how is it 92 billion lightyears wide?”. (Oversimplified.)

I don’t think I opened it for the answers. Perhaps I should have.

Then today I saw a question here about the speed of differs with light moving through different substances (oversimplified, thread in question is here ).

Could an answer to the first question be that the universe at the moment of the big bang wasn’t a vacuum? Is this related to the undetectable dark matter that is pushed outward with the growth of the universe?

Yes.

Last night ISS was flying over my location (southern Ontario, 6:48 EST) and it was clear for the first time in weeks, so I went outside to see it. To my delight, there was a second smaller object orbiting about 1 degree ahead of the station.

https://imgur.com/a/XIiuGZm

I looked on all the lists of departures and arrivals I could find, but I could not get an identification for it - not Soyuz, not Dragon. Am I missing something? Any clues?

It's still the same total energy. You'll lose ice getting down to minus whatever degrees, so while you're colder to start, you also have less ice.

Ignoring all the extra stuff that can happen (e.g. condensation on the outside of the colder cooler dumping extra energy into it, or freezing and making an insulating layer), a sealed ice+salt cooler should hit 1 degree Celcius before a sealed cooler with ice alone would.

What makes the case for dark matter more valid than "something must be wrong with the calculations/measurements" or indicative that there are laws/interactions we haven't figured out yet?

Since it can't be measured in anyway other than otherwise unexplained phenomena, it feels like, "We can't explain what's happening, therefor there must be dark matter,"

Adding salt makes it colder but it would cause the cooler to reach room temperature slightly faster. The rate at which something heats up depends on the difference in temperature between the object and its surroundings—very cold objects heat up quickly at first, then heating slows down as they approach room temperature. Melting ice uses up heat energy to break the bonds holding the ice together as a solid.

When you add salt, the ice absorbs all the heat energy it already has in order to break those bonds, which causes the temperature to drop below the normal freezing point. The resulting water is colder than the ice it came from and the water conducts heat better than ice, so the water warms up quickly until it gets warmer.

When you don’t add salt, the temperature will pause at 32F/0C until all the ice is melted. When the ice absorbs heat energy from its surroundings, that energy goes to changing the ice into water instead of increasing the temperature. The ice will absorb heat at a slower rate than the super cooled salt water because the ice is warmer than the salt water and because ice doesn’t conduct heat as easily as water does.

Yes but the thing is we don't know the limit precisely. Eventually, as you add more and more protons and neutrons together, they stop being bound together. This is known as a Proton or Neutron dip. Idk how much 500 protons would even be like but it'd have a very very small lifetime. Micro if not nano or picoseconds.

Depends. There's lots of reasons it shouldn't work yet it isn't forbidden by relativity. The main problem with it is that it requires negative pressure and we have no idea if it even exists. Negative pressure= negative energy=negative mass. Literally, -1 kg.

And even then, we would only be able to contract and expand spacetime to a finite extent before we run into the fact that it would require more negative pressure than the energy in the observable universe. That's impossible.

When we mean ‘falling’ we talk of being captured in a gravitational well and being forced to move around it if the body is rotating. And you can fall in accordance as long as you share a barycenter. So yes, we are technically falling in the Local Group's gravitational well.

>If everything is falling does the expansion of space mean there’s always room for everything to continuously fall?

Eh..... roughly yes.

No. The math doesn't work out the same. You can use Classical Physics to explain things like Feynman Diagrams and you can't use QM to explain the universe at a large scale.

That's only their perspective. To us they move but to their perspective, distance doesn't exist at all as the time they were created and the time they were emitted are the same time. It's just a consequence of Relativity.

No, not at all. See "enthalpy of fusion". Ice melting is endothermic, it has to take in heat from the environment to happen. By forcing it to melt earlier it pulls in heat energy and makes it's surroundings cooler than they were before. However this isn't violating the law.of conservation of energy because the act of freezing the water is exothermic, it gave off heat energy when freezing. It would violate the laws of conservation of energy if it didn't make it colder because then it wouldn't be balanced with the exothermic freezing.

Instant cold packs work on the same principle. Also, this is really easy to verify in your kitchen with some salt, ice, and a thermometer.

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Physics: If time stops at the speed of light then how do light photons move at all? If time stopped for me would I not be essentially stuck in the same place unable to move until time started for me again?

In Newtonian physics as long as you have a constant force you can accelerate forever, right?

So you're saying salt has the magical ability to violate conservation of energy?

Imagine you’re standing on a globe and on the other side there’s a point (the singularity). Every direction you walk is towards the singularity. It’s kinda like that but with another dimension

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How is it impossible for ice to be between -10 and -20? I have my freezer set to -18°C, and everything that has been in there long enough is also -18°C

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The reason for adding the salt to the ice is the reason we add salt to ice in ice cream makers. The salt causes the ice to melt, which is an endothermic process. This means it needs to get energy from somewhere, and that somewhere in ice cream making is by cooling the cream/custard. In the case of the fishermen, it just means the fish is cooled quickly.

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Uh, no, releasing the cold quickly or slowly does not change the total amount of coldness that there is to be released.

I remember this as a kid too - we didn’t have the ice cream maker but we used one big coffee can, a smaller can inside and the rock salt ice in the space between. You had to shake it until your arms felt like they would fall off.

Why is there a difference in physics in general, and the physics in quantum mechanics, or is there any? From my understanding, it's a difference of forces, but does the math not work out the same?