Strange is our situation here on Earth. Each of us comes for a short visit, not knowing why, yet sometimes seeming to divine a purpose. From the standpoint of daily life, however, there is one thing we do know: that man is here for the sake of other men - above all for those upon whose smiles and well-being our own happiness depends.
The most beautiful thing we can experience is the mysterious. It is the source of all true art and science.
Happy 138th birthday to Albert Einstein, one of the brilliant fathers of modern physics and the founder of physical cosmology and relativity.
The fact that we live at the bottom of a deep gravity well, on the surface of a gas covered planet going around a nuclear fireball 90 million miles away and think this to be normal is obviously some indication of how skewed our perspective tends to be.
Douglas Adams, The Salmon of Doubt: Hitchhiking the Galaxy One Last Time
Of all the places in the entire universe, there is probably nowhere more mysterious than the inner workings of a black hole. This is because the two most accurate theories humans have ever created disagree about what happens in the center of one.
When a large star runs out of fuel, it no longer has the energy to resist its own gravity and starts pulling in on itself. If nothing stops the collapse before a certain point, the gravity will become so strong that not even light can escape. At this point, the star becomes a black hole; a massive celestial body that has the ability to tear apart stars.
For the most part, we have a good idea for what happens in the space around a black hole. Einstein’s theory of General Relativity tells us that black holes, as well as other massive objects, bend the fabric of space and time, leading to strange events such as time dilation. But the main point of controversy isn’t what happens around a black hole, but what happens in the very middle; the singularity.
General Relativity states that if a piece of matter falls into a black hole, it gets crushed into a single point in the center. Here, any information about what fell in is completely obliterated. However, quantum mechanics tells a different story. It is a well known rule in quantum physics that quantum information can’t be destroyed, and there must be some ambiguity to a particle’s position. Clearly, something is off here.
There are a lot of different theories that attempt to solve this riddle, often involving extra dimensions or new particles beyond the Standard Model, but none of them seem to be currently testable. But it’s possible that someday, someone will give us a new, testable theory, and it will give us insight into the inner working of black holes, and maybe even the first few moments of the Big Bang.
If you and I are in separate space ships both traveling fast, there’s literally no possible way to determine if I am staying still and you are moving, or if you are staying still and I am moving, or if we are both moving. Also, from your perspective time will flow normally for you and slower for me, but from my perspective time will flow normally for me and slow for you.
Basically, everything, including time, is completely relative.
“You can witness the evolution and destruction of humanity; the end of the Earth and Sun; the dissociation of our galaxy; the heat death of the Universe itself. So long as you have enough power in your space ship, you can travel as far into the future as you like.”
Have you ever wondered about time travel? Perhaps you have your destination in the far future, and want to see how it all turns out? Maybe you want to return to the past, and alter the future or present by your actions there? Or maybe you want to freeze time altogether? If you want to know whether it’s possible, the physics of relativity holds the answer. Special relativity allows us to control our motion through time by manipulating our motion through space. The more we move through space, the less we move through time, allowing us to travel as far as we want into the future, limited only by our energy available for space travel. But going to the past requires some specific solutions to general relativity, which may (or may not) describe our physical Universe.
The famous image of Einstein’s desk, exactly how he left it, mere hours after his death
Before his passing Einstein had refused the surgery for the internal bleeding that subsequently took his life; saying: “I want to go when I want. It is tasteless to prolong life artificially. I have done my share, it is time to go. I will do it elegantly”.
As can be seen here with the mountains of shuffled paper and scribbles on the blackboard, Einstein certainly did do his part and worked until the very end.
Does time actually exist? I personally dont think that it really exists...
Time, as described by Einstein’s theories of relativity, certainly does exist. The duration of time between two events is just as real as the distance in space between two objects, and according to Einstein, these two qualities are actually tied together. This is where the concept of space-time comes from, and it has some profound consequences.
Not only does time exist, but it can be stretched, bent, and warped. The flow of time can change depending on how fast you are moving, and how close you are to a massive object. The same can be said for space, too, but I don’t think anyone is debating how ‘real’ space is.
Now, the human perception of time may not be entirely real. Our brains aren’t perfect clocks, so we’re bound to be a little bit off. Not to mention, one can make the argument that all of human perception is an illusion, but I digress. That being said, our perception of time is a decent approximation.
If a black hole got an object with a huge mass in it then why is the hole in only one direction?
I’m assuming you’re referring to pictures like this one
which imply that black holes are a hole in one of our three spatial directions, and stuff can only enter through a ‘plane.’ In reality, black holes are spherical, meaning any object can enter from any angle and go into the black hole; the hole goes in all directions, as shown by this image:
However, this image that accurately shows what a black hole would look like to us, it doesn’t show us the extreme warping of space around a black hole, which is where the misconception arises: from scientists trying to depict the warping of space and time around a black hole. It’s very hard to visualize the warping of three dimensional space, and even harder to create a two dimensional image depicting a three dimensional warping, so they essentially remove one dimension - think of it as a cross section. This way of illustrating it shows how dramatically curved space and time are around a black hole, but they also imply that a black hole goes “down” in one of our directions, and that matter can only enter one way, which is false. Sorry if I did a poor job of explaining - let me know if you have any more questions!
Ask Ethan: What Happens When A Black Hole’s Singularity Evaporates?
“What happens when a black hole has lost enough energy due to hawking radiation that its energy density no longer supports a singularity with an event horizon? Put another way, what happens when a black hole ceases to be a black hole due to hawking radiation?”
One of the most puzzling things about Black Holes is that if you wait around long enough, they’ll evaporate completely. The curved spacetime outside of the event horizon still undergoes quantum effects, and when you combine General Relativity and quantum field theory in exactly that fashion, you get a blackbody spectrum of thermal radiation out. Given enough time, a black hole will decay away completely. But what will that entail? Will an event horizon cease to exist, exposing a former black hole’s core? Will it persist right until the final moment, indicative of a true singularity? And how hot and energetic will that final evaporative state be?
I'm pretty young but I love astrophysics and I was wondering if you had any sort of list of resources (books, websites, etc) that explains and discusses quantum mechanics, the theory of relativity, and general theoretical physics.
Thanks for asking!! I’m glad that you’re interested in learning more about space and astrophysics, especially since you’re young.
I really really like PBS SpaceTime, they have a lot of SUPER interesting and very well done videos about all of the above mentioned topics (i’m actually probably gonna post some of their really good vids eventually). And when I say they have a lot of videos, I mean a LOT. And they’re all really really informative and very scientifically accurate. 15/10, would recommend.
If you want very in-depth articles, wikipedia is a relatively (pun intended) good source for reading about scientific topics - one of my friends jokingly said that wikipedia is where grad students record all the stuff they’ve learned so they don’t forget it in a few months (lol). Also a lot of universities have online notes and stuff posted, any website with a .edu ending is DEFINITELY trustworthy and likely to be accurate. I don’t have any book recommendations right now, but I’m going home for the weekend and I want to look at some if I get the chance. You can always find really good science books in the science section, right now I have “physics of the impossible” by Michio Kaku, and it’s a really cool book.
Let me know if you have any other questions, I’m happy to answer them and I really enjoy getting asks!
LIGO’s Successor Approved; Will Discover Incredible New Sources Of Gravitational Waves
“The huge advance of LISA, though, will be the ability to detect objects spiraling into and merging with the supermassive black holes at the centers of galaxies. Stars and other forms of matter are constantly falling into black holes at the galactic center, both in our own galaxy and well beyond. These events often result in the ejection of matter, the acceleration of charged particles and the emission of radio and X-ray light. But they should also result in the emission of gravitational waves, and LISA will be sensitive to those. For the first time, we’ll be able to see supermassive black holes in gravitational waves.”
There’s no doubt that LIGO has given us one of the most incredible breakthroughs of the 21st century: the direct detection of gravitational waves. But as wonderful as LIGO is, so far it’s only been able to detect the very final stages of mergers of stellar mass-scale black holes, and only every few months at that. The technique of laser interferometry is sound and powerful, but properties inherent to Earth itself fundamentally limit how good LIGO can potentially be. But these restrictions go away if we go to space! Not only can we eliminate seismic noise, cease accounting for the curvature of the Earth, and get a better vacuum for free, but we can achieve much longer baselines. By sending a series of spacecraft up into orbit behind the Earth, we can detect more massive, more distant, and slower-period sources than LIGO could ever hope to see.