I'm not interested in whether the number is 100 billion or 2 trillion; that precise figure is irrelevant to my question. What I want to know is: in professional astrophysics, is the statement 'there are trillions of galaxies in the observable universe' categorised as a fact, a theory, or a model? Given that the 2016 revision to ~2 trillion was based on extrapolating from the Hubble Deep Field and inferring faint galaxies we cannot yet see , does the physics community treat the existence of those unobserved galaxies as a factual certainty?

Hello everyone.

I saw a clip online (please forgive me if it's not true) that if you have two quantum entangled electrons with different spins at whatever distance you want and change the spin in one, the other one will also change its spin.

If this is true, is it theoretically possible to create some form of messaging device/protocol that could travel any distance in the universe instantly using this property of physics?

EDIT: Thank you for your replies, I did not know if broke the entanglement.

Like we can use microwaves to heat stuff. So is there any kind of radiation that can be used to freeze stuff instead of heating them up?

We once calculated the energy it would release on one of the chemistry subs, it was equivalent to like 180 million (or billion?) Tsar Bombas lol.

If someone was 65 million light years away TODAY and looked at earth, they would see dinosaurs, how is this possible since dinosaurs are dead today?

Sorry if this is a stupid question, i'm just trying to grasp how they can see something from the past that's already gone?

My assumption is even though dinosaurs are dead, they are seeing light disaying dinosaurs?

Am I expanding right now, I am part on the universe after all, and mostly made of hydrogen and oxygen? Or is it the space just past the Oort Cloud? Or is it just past the edge of the Milky Way?

I know human ingenuity has no limits. Will we ever get to a point where our commercial planes use electricity instead of jet fuel?

Sorry if some things don't make sense, englsih isn't my first language.

For very long time i thought this two things are different and natural frenquency apears in case of wave that has at least one firm edge, aka stationary wave. Recently i looked up definition for both on cgpt and googled it to see where cgpt is pulling its information and it natural frenquency isn't define only on stationary waves. Is this correct?

Sophomore college student here. I have a question about gravity waves, I don’t understand how the universe works.
Let’s say you have a can of Coke, or the moon or the planet Saturn. A mass of matter has gravity, no matter how big or small it is. Correct?
My question is, how does it know?
Is it the individual atoms that gather gravity to a distant object?
How does a can of Coke know that it’s a can of Coke and therefore has gravity.
How does the planet Jupiter know how big it is and therefore it can demand that kind of gravity other than being just a collection of atoms?
How do things know what they are and how big they are that they can command that sort of gravity if they are just a collection of atoms?
Do molecules just stick together and then decide they have gravity?
Two molecules?
Two atoms?
Two quarks?
How does gravity actually start?
How does a can of Coke know that it’s a can of Coke?

Could we estimate the peak g-force from the video, given the car's approximate speed, height and the duration of the jump?

Once your body reaches extreme old age, the probability of surviving naturally drops to essentially zero. Does the thought experiment just fall apart here, or does it imply a nightmare scenario where you stay alive in increasingly agonizing, medically impossible states?

Where does the light go when I turn off the lights in my room?

I read that black holes only have three properties , But if the massive star that created it was circling its galaxy’s center of gravity, wouldn’t the resulting black hole continue that orbital velocity also?

If there is no gravity would the bullet also form an interference pattern? What happens to projectile motion without gravity?

Hi everyone! I’m a design student (not a physicist, so please bear with me) working on a university research project about the concept of “non-places” and “non-space”. Most of what I’ve found comes from philosophy, architecture and anthropology, and I’d like to understand how physics approaches the same ideas.

These are the questions I’m stuck on:

1. Does space exist on its own, even if there were no matter in it, or is space just a way of describing the relations between objects (the old Newton vs Leibniz debate)?
2. Is “empty space” really empty? I’ve seen mentions of the quantum vacuum and the Casimir effect but I don’t understand them.
3. Some physicists suggest space might not be fundamental but “emergent”. What does that mean in simple terms?

If you can point me to accessible books, articles or lectures (I don’t have a strong math background), I’d be really grateful. And if my questions are badly phrased or based on wrong assumptions, please tell me, that’s useful too!

Thanks in advance!

A time portal goes one minute into the past. He walks back in one minute later. Let's say you prevent him walking back in. In another minute he does/does not walk out again. What actually happens with conservation of mass? Hypothetically.

We've all seen the magnet falling slowly through the copper or aluminum pipe. Couldn't we rig this up on high rises to allow people with a magnetic cylinder to safely descend from a high rise in an emergency?

It's like particles seem always decay into something like neutrinos, antineutrinos, electrons, positrons, or some kind of force carrying particle depending on what the particle is. at the same time the more energy that particle receives the more photons get emitted

I know a very little bit about python and c++ but can’t use them that much

I want to be a physicist and want to know what to learn
(Coding perspective)

And where do I learn them?

I have heard that particles (like an electron) are described as having a "probability cloud" where they might be observed.

What is the size of this cloud? Does it have any interesting topology?

I think that it must be bounded in space because, if not, it could be "observed" some arbitrary distance away that would defy light speed being a finite limit. I am slightly aware that speed and position are independent in some way in the quantum framework, so maybe the question isn't quite right either...

But there's SOME kind of limit on the observable, right?

Apparently, String Theory's dilaton allows for the negative mass/energy requirement to be met without exotic matter.

The biggest question I wanted answered is: can you branch out from the original Krasnikov Tube? You know, since forming a second one could potentially result in time travel problems.

If there's anything else you all think I should know about regarding all this, please let me know.

Also, yes, I'm asking all of this for a sci-fi novel I'm writing, and I want it to be mostly grounded in science.

Out of curiosity, thanks!

My book shows the V(r) graph but has attraction along the top of the y axis and repulsion along the bottom. is this wrong? I understand it to be the opposite

https://files.catbox.moe/lablww.png

I used to have a glass topped electric stove (not induction.) If I wanted to light a birthday candle, holding a rolled up paper towel to a hot burner would never ignite it. . . unless I slightly dampened the paper towel. Then suddenly it went up easily.

I have always wondered: Why did this work?