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.
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.
In Einstein’s General Theory of Relativity, space and time are unified in a single entity called spacetime. This is the “stage” in which the laws of physics operate.
In Einstein’s theory, the presence of mass and energy warps spacetime, and it is this curvature that affects objects in the way we perceive as gravity. The basic idea is that while we see objects accelerating towards a mass by the effect of a force, in reality is just the object attempting to follow a straight line in this four-dimensional warped space described by General Relativity.
In other words, things fall because they are following a straight line in spacetime.
In usual illustrations, the bending of space is represented as a flat rubber-sheet with masses pressing down on it. This has always bugged me, as it didn’t really represent the nature of 3D space being curved, and it never really addressed the fact that time is also distorted near masses.
This is my first attempt at a better depiction of the effects of General Relativity. Here, we see a 3x3x3 section of an imaginary spatial grid (that extends throughout all of space) being distorted by the presence of a mass. At the intersections of the grid lines there are clocks that show the rate of passage of time at each point in space, relative to a far away observer.
Notice how the clocks near the mass measure time at a slower pace than the clocks further away from the mass.
The distortion of spacetime is real, and can and has been measured experimentally several times. Modern telecommunication satellites and GPS systems all make use of the predictions of General Relativity in order to function.
While bizarre and complex, General Relativity has stood the test of time, and is one of the most well-tested and successful scientific theories ever conceived.
“You might then ask, at what distance does the expansion start to take over? That happens when you average over a volume so large that the density of matter inside the volume has a gravitational self-attraction weaker than the expansion’s pull. From atomic nuclei up, the larger the volume you average over, the smaller the average density. But it is only somewhere beyond the scales of galaxy clusters that expansion takes over. On very short distances, when the nuclear and electromagnetic forces aren’t neutralized, these also act against the pull of gravity. This safely prevents atoms and molecules from being torn apart by the universe’s expansion.”
The Universe is expanding. The farther away a galaxy is, the faster it appears to be receding from us. The standard story tells us that space itself is expanding, and that’s the cause, but it’s only natural to wonder if perhaps space is static, and everything else within it isn’t shrinking instead? Many laypersons choose to go this route, and question the entire field of cosmology as a result. But is this fair? Or is this a road to not only ruin, but to physical inconsistencies? Could we flip the story on its head, and do some sort of test to see if atoms, the planet, or some other ‘local’ entity is shrinking, instead? Or, using the principle of relativity, could we declare that all frames are equally valid, and choose a frame where space isn’t expanding, after all?
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.
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 there is energy within the substance it can only come from without. This truth was so manifest to me that I expressed it in the following axiom: ‘There is no energy in matter except that absorbed from the medium…’ If all energy is supplied to matter from without then this all important function must be performed by the medium.”
“When radio-active rays were discovered their investigators believed them to be due to liberation of atomic energy in the form of waves. This being impossible in the light of the preceding I concluded that they were produced by some external disturbance and composed of electrified particles. My theory was not seriously taken although it appeared simple and plausible. Suppose that bullets are fired against a wall. Where a missile strikes the material is crushed and spatters in all directions radial from the place of impact. In this example it is perfectly clear that the energy of the flying pieces can only be derived from that of the bullets. But in manifestation of radio-activity no such proof could be advanced and it was, therefore, of the first importance to demonstrate experimentally the existence of this miraculous disturbance in the medium. I was rewarded in these efforts with quick success largely because of the efficient method I adopted which consisted in deriving from a great mass of air, ionized by the disturbance, a current, storing its energy in a condenser and discharging the same through an indicating device. This plan did away with the limitations and incertitude of the electroscope first employed and was described by me in articles and patents from 1900 to 1905. It was logical to expect, judging from the behavior of known radiations, that the chief source of the new rays would be the sun, but this supposition was contradicted by observations and theoretical considerations which disclosed some surprising facts in this connection.
“Light and heat rays are absorbed in their passage through a medium in a certain proportion to its density. The ether, although the most tenuous of all substances, is no exception to this rule. Its density has been first estimated by Lord Kelvin and conformably to his finding a column of one square centimeter cross section and of a length such that light, traveling at a rate of three hundred thousands kilometers per second, would require one year to traverse it, should weigh 4.8 grams. This is just about the weight of a prism of ordinary glass of the same cross section and two centimeters length which, therefore, may be assumed as the equivalent of the ether column in absorption. A column of the ether one thousand times longer would thus absorb as much light as twenty meters of glass. However, there are suns at distances of many thousands of light years and it is evident that virtually no light from them can reach the earth. But if these suns emit rays immensely more penetrative than those of light they will be slightly dimmed and so the aggregate amount of radiations pouring upon the earth from all sides will be overwhelmingly greater than that supplied to it by our luminary. If light and heat rays would be as penetrative as the cosmic, so fierce would be the perpetual glare and so scorching the heat that life on this and other planets could not exist.
“Rays in every respect similar to the cosmic are produced by my vacuum tubes when operated at pressures of ten millions of volts or more, but even if it were not confirmed by experiment, the theory I advanced in 1897 would afford the simplest and most probable explanation of the phenomena. Is not the universe with its infinite and impenetrable boundary a perfect vacuum tube of dimensions and power inconceivable? Are not its fiery suns electrodes at temperatures far beyond any we can apply in the puny and crude contrivances of our making? Is it not a fact that the suns and stars are under immense electrical pressures transcending any that man can ever produce and is this not equally true of the vacuum in celestial space? Finally, can there be any doubt that cosmic dust and meteoric matter present an infinitude of targets acting as reflectors and transformers of energy? If under ideal working conditions, and with apparatus on a scale beyond the grasp of the human mind, rays of surpassing intensity and penetrative power would not be generated, then, indeed, nature has made an unique exception to its laws.
"It has been suggested that the cosmic rays are electrons or that they are the result of creation of new matter in the interstellar deserts. These views are too fantastic to be even for a moment seriously considered. They are natural outcroppings of this age of deep but unrational thinking, of impossible theories, the latest of which might, perhaps, deal with the curvature of time. What this world of ours would be if time were curved…“
“The Eternal Source of Energy of the Universe, Origin and Intensity of Cosmic Rays.” October 13, 1932.
“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.
Follow up question, are black holes funnel shapes? And if so why?
I’m guessing you’re referring to images like this, which show black holes to appear funnel shaped
To summarize, objects warp space and time. To make it easier to imagine, representations are taken down to two dimensions, so you can see how an object warps space and time. The more massive the object, the more it warps time. Black holes theoretically warp space and time infinitely at the singularity (where any amount of matter can be compacted, in some cases millions of suns).
The black hole appears funnel-shaped because the curvature of space increases as you approach the black hole, and then becomes infinitely curved and infinitely steep when you reach the singularity. It’s misleading, but it does help visualize how they warp space. Black holes in reality are spherical, as they warp space in all directions (that’s why these images take it down a dimension to make visualization infinitely easier).
I hope I did a good job with this - it can be pretty hard to wrap your head around it, let me know if you have any other questions.
The Mythbusters tested what would happen if a ball was shot at 60 mph off the back of a truck travelling at 60 mph to see what would happen.
It became a perfect example of the relative nature of physics - showing that velocity can vectorially add together. 60 mph in one direction cancels the 60 mph in the other, meaning a net velocity of zero.
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.
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?
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!
“According to the Relativists, space has a tendency to curvature owing to an inherent property or presence of celestial bodies. Granting a semblance of reality to this fantastic idea, it is still self-contradictory. Every action is accompanied by an equivalent reaction and the effects of the latter are directly opposite to those of the former. Supposing that the bodies act upon the surrounding space causing curvature of the same, it appears to my simple mind that the curved spaces must react on the bodies and, producing the opposite effects, straighten out the curves. Since action and reaction are coexistent, it follows that the supposed curvature of space is entirely impossible. But even if it existed it would not explain the motions of the bodies as observed. Only the existence of a field of force can account for them and its assumption dispenses with space curvature. All literature on this subject is futile and destined to oblivion. So are also all attempts to explain the workings of the universe without recognizing the existence of the ether and the indispensable function it plays in the phenomena.”
“DYNAMIC THEORY OF GRAVITY.” July 10, 1937 (Prior to interviews with the press on his 81st birthday observance).
Fooling around with some PhD qualification problem sets. Mid term break next week so study and contact courses will be on the cards! After break, it’s pretty much a straight lead up to exams so here’s a reminder to stay on top of your game- don’t neglect your papers before exams and then just cram in the last couple of weeks. By remaining constantly vigilant and on top of it during the earlier half of semester, you won’t need to work so hard to retain important concepts! Wishing you all happy and healthy studies 💕