I don't know about anyone else but I'm pretty fascinating by black holes! I think that black holes are very interesting. They can be extremely large. For years I thought nothing compared in size to the star UY Scuti, which has a radius 1700 times larger than the sun. When I learned about the TON 618 black hole, I couldn't believe how much larger it was than UY Scuti. It feels like comparing the size of an atom to the size of a country.

https://www.youtube.com/watch?v=FBchtofZJSM

But their potential size is definitely not the only thing interesting about black holes. As long something has mass, any thing and any person can become a black hole, just as long as it's condensed into a small enough size so ridiculously dense, that even light cannot escape its gravitational pull. This is almost unfathomable to really think about, but to give an example, the earth would have to be condensed down to the size of a penny in order to form a black hole.

Another thing that's pretty interesting to imagine is what would happen if a black hole were to suddenly form on our planet. Black holes basically swallow everything that has mass, just as long as they're close enough to it. So let's say Teddiursa figured out a way to condense a human into a space just 1 sextillionth times smaller than a grain of sand. This person would become so unbelievably dense that they would die, but their dead body would become a black hole.

If this were to happen, the black hole would basically eat away at everything in sight, swallowing the earth from the inside, but leaving the rest of it a scattered disc of hot rock. (At least this is what I believe the outcome would be based on a video I watched and one article I read).

But I'm no expert and I have a question for anyone who may know more than me about black holes. If a black hole can't feed off of anything, it simply evaporates, but it releases enough energy to destroy basically everything in sight (Energy it releases would be equal to many million or billion+ megatons of TNT, which depending on the size could be an unfathomable number of times more powerful than any nuclear weapon we ever detonated).

However, if a black hole does have matter to feed upon, it continues to grow while it swallows mass. Are these two different outcomes the result of different size black holes? Both outcomes would destroy the entire world (maybe unless the black hole is extremely small), but one vanishes and the other continues to grow. My assumption is that if a black hole is too small it won't be able to swallow mass easily. Would the black hole just evaporate if it's really really small, while the bigger one would grow and live on?

Well you got it wrong. Evaporating of black holes is extremely slow. So slow that although the amoáunt of released energy is indeed huge, it is distributed through so big stretch of time that if you would observe black hole in evaporating state, you will notice hardly anything.
The last state will be explosion of black hole indeed, but it is so small at that time (black holes are shrinking when evaporating of course) that its size is at subatomic level at this point. Resulting explosion would be unnoticeable by human senses.
If black hole will shirnk or grow has nothing to do with its size, but it depends solely on if there is any matter it can use in its surroundings.
I higly recommend to watch this playlist: https://www.youtube.com/playlist?list=PLsPUh22kYmNBl4h0i4mI5zDflExXJMo_x There you can learn literylly anything we know on them so far. Enjoy!

Would recommend watching https://youtube.com/watch?v=KUbnuMFA78w.

Did you know that there are theorised to be white holes as well? https://youtube.com/watch?v=pTmidUC3BT4

According to this: https://en.wikipedia.org/wiki/Hawking_radiation , Blackholes with a mass of 2,28 x 10^5 kg would evaporate in just a second. Which means that if a human turned into a blackhole, they would evaporate before they even ate up enough mass to create a chain reaction. The energy realeased can be calculated with the mass-energy equivalanece E=mc^2. So incase of the one descibed above, that would be 2.05x10^22 J,. WHich is roughly the chemical eneergy of 5million megatons of TNT. However in the case of the blackhole, the energy would be realsed as a gamma burst. Which means that instead of an explosion, you have an expanding bubble of superhot plasma, since the air around would be ionised almost instantly.

Edited 8/25/2018 12:44:29

Didn't bothered myself with calculations, thanks for correcting me Cata.

Only big black holes last for long.
Black holes could prove the 4th dimension because:

The singularity has a diameter of 0 whatever measure, and when things get sucked into a black hole and into the singularity, they'd overlap, which violates everything.

A "theory" would be that they'd go another "universe" (another 3d place in an 4d space), and the thing that they'd come out of would be a "white hole". Sadly, we cannot test this, as a person would be spaghettified before seeing if the theory was true.

^
Time is the 4th dimension.

And singularity doesnt violate anything. It conflicts with the classical physics, in which infinite density is not possible. However general relativity is perfectly fine with a black hole. Infact relativity is the only way to even describe them.

The only problem black holes cause is that information is lost when objects pass the event horizon. The only information preserved are mass, electric charge, and angular momentum. This is basically why relativity and quantum physics are not entirely compatible. Singularity violates the Pauli exclusion principle, which states that 2 fermions (or particles in general) must differ by atleast 1 quantum state.

The theories of white holes as of now are rather baseless, and entirely hypothetical.

It is a THEORY that time is the 4th dimension.
And if infinite density were possible, Black Holes would generate infinite energy, which is not possible.

is time travel possible?

Time isn't the fourth dimension you dip. The fourth dimension exists in theory. See: the hypercube. Dimensionality is an attribute of space, not time.

Time does not exist as such. A 4d multiverse with 3d universes comprising it HAS time itself if it has a history and a future; otherwise it could be a still photograph and have the same spacial dimensions.

Edited 8/28/2018 17:51:32

It is a THEORY that time is the 4th dimension.
And if infinite density were possible, Black Holes would generate infinite energy, which is not possible.

A well accepted theory.
And infinite density only violates classical physics and quantum mechanics, but not relativity. Why would it create an infinite amount of energy?

is time travel possible?

In our current understanding, 4D-beings can only travel into the future. If you want to accerlate that process you have to enter an extremely strong gravitional field, or accelerate close to the speed of light. Satellites are known to correct their inner clocks by fractions of milliseconds, because of their orbital speed around Earth, and lower gravitiy they experience. They are basically proven time travelers.

Time isn't the fourth dimension you dip. The fourth dimension exists in theory. See: the hypercube. Dimensionality is an attribute of space, not time.

Tesseracts and higher hypercubes are just a visual representation of higher dimensions. They are not actually the dimensions. It is well accepted in the scientific community that spacetime is the 4th dimension.

>tesseracts are just a visual representation of a higher dimension. They are not actually the dimensions.

I'm not saying a tesseract IS a dimension I'm saying it is a tangible figure in 4D space. It has 4 dimensions.

>It is well accepted in the scientific community that spacetime is the 4th dimension

So? Assuming you aren't lying that's the whole point of discussing these things. The minority who disagree need to make their case. We don't say consensus has been achieved and stop talking about it.

A theoretical geometric figure with 4, 5, 6 etc. dimensions has space. It does not necessarily have time. Time is direction. If the figure was blue at t0 and red at t5 it has time. If the figure belongs in a still photograph it does not have time.

Edited 8/28/2018 19:48:39

A theoretical geometric figure with 4, 5, 6 etc. dimensions has space. It does not necessarily have time. Time is direction. If the figure was blue at t0 and red at t5 it has time. If the figure belongs in a still photograph it does not have time.

The thing is that, in our current understanding there are no geometrical figures with more than 3 dimensions - Length, width, height. There is no 4th geometrical dimension. However there is time. Like a cube can change over time. Think of time like an geometrical dimension that we cant control. For example a theoretical 5-dimensional being could control time, and move in it. Back and forth. We cant do that, because we are only 4-dimensional. Instead we can only control the 3 dimension below us.

A physics thread making it to this forum is an impressive quality boost.
Black holes are very interesting and general relativity predicts some interesting effects. You can try looking up rotating (Kerr) black holes, frame dragging, ergosphere and the cosmic censorship hypothesis, those are some of the less commonly known aspects.

In special relativity you work in a 4D space, Minkowski space, with time as a 4th dimension, and in general relativity you work with a more general 4D spacetime that can be 'curved', describing gravitational effects. Unlike in classical physics where time is a global parameter, time is observer-dependent in relativity.

Whether you want to call time a dimension or not is more like a semantic discussion about how you want to define the word dimension. Wulfhere's comments aren't going to tell us any facts about physics but only that when he says dimensions, he will always mean spatial dimensions, and his arguments for why time isn't a dimension is always that it's not like a spatial dimension, and you're a dip if you disagree. The professor who taught me in a course on general relativity happily refers to spacetime as 4-dimensional so it's not something I would worry about.

Time doesn't necessarily have to be the 4th dimension, you could also make a physical theory of a universe with 4 spatial dimensions and a 5th time dimension, or even 2 time dimensions if you like. If you work on laser physics maybe you would look at how much you can excite a collection of atoms with a certain laser power, make a plot with a time axis and power axis, and call power a dimension in this system. That's not to say there's a deep physical meaning to the laser power on a universal scale but just how it's common to call parameters "dimensions" when you use them in some coordinate system that helps to explain whatever you study. But in common language it's mostly associated with space and time so here most people probably associate it with the big universal implications from relativity.

Time is the 4th dimension is if string theory is true.
The 4th spatial dimension is if... something else is true.

It's fascinating to think about what could be inside of a black hole. It's cool how once you compress an object to a certain radius for its mass so that it acquired a certain density (its Schwartzchild Radius), it spontaneously collapses on itself due to its own gravity. Unfortunately with current technology we are unable to reveal the innards of the event horizon of a black hole in practice, but computer simulations can be used, and postulates and hypotheses can be constructed. I was thinking about how matter/energy cannot be created nor destroyed based on the first law of thermodynamics, and how a true singularity would break the current known setup of physics, and have thought that possibly within a black hole is quark matter, where the gravitational force of the matter caused the subatomic particles to disintegrate into quarks, of which end up compacted densely enough to resemble a singularity, but still has some sort of dimension. The matter that falls into a black hole could be converted into pure energy or electromagnetic radiation, due to the incredible amount of kinetic energy that is being held by the matter as it crosses the event horizon. The impact, if there were one, on the central quark matter core, along with the ridiculously intense gravity, could cause the matter entering to disintegrate into quarks and energy, therefore keeping in line with thermodynamic laws, and explaining the massive amount of x-rays emitted from the poles of the black hole. Of course, some of that matter would join the hypothesized "core" of the black hole, increasing the mass, and therefore radius of the event horizon. As long as there is enough influx of matter, the change of mass of a black hole should still be a net positive to counteract decay and release as Hawking radiation.

Sorry about this long wall of text, it's late and I should be going to bed and I probably rambled. Science is cool tho.