Both Physicists worked or are working in the field of General Relativity and the papers are stabs at Quantum Gravity, Black Hole, Physics, The early big bang and whether or not it is a spacetime singularity and Black Hole Entropy and Hawking Radiation. These ideas show up all over the place in popularizations of theoretical physics and cosmology.
I looked at the papers. They are admittedly above my level of expertise.
The Nature of Space and Time
I didn A seminal collection of papers from Hawking and Penrose from the s. I didn't study General Relativity as an undergrad in Physics but I got bits and pieces of the argument. Worth a look but someone who did grad level Physics would get more out of it. Mar 07, Wanyoung Kim rated it really liked it. Lots of diagrams. Has a lot of loaded philosophical statements that were useful when writing a thesis. Helps to explain singularity, cosmic censorship, etc. Jun 12, Todd rated it it was ok. That said, one big problem I have with thi "Time is the fire in which we burn. That said, one big problem I have with this is that he mentions god several times, and given there is no proof of god, why is he continually referring to a scientific "nothing" in his lectures?
Even though I am not a scientist, the fact he mentions god tells me his science is not completely rooted in reality but rather at least in some part is rooted in mythology, and that tells me he lives in a world in which I do not live. I gave it a good college try, but was immediately swamped by the intense theoretical physics and deep mathematics involved.
As a series of lectures between the two physicists as they voice disagreements about the nature of the universe, it was interesting to be a sort of fly on the wall, to see what these big brains talk about when the rest of us aren't around. On the other hand, they're discussing these things at their own level and not the level of a layman, so one might as well be a fly on th I gave it a good college try, but was immediately swamped by the intense theoretical physics and deep mathematics involved. On the other hand, they're discussing these things at their own level and not the level of a layman, so one might as well be a fly on the wall for the comprehension of the subject is concerned.
I gave up after failing to understand even the nature of the disagreement. Sep 13, Jeff rated it liked it. This is collection of essays is an argument between Hawking and Penrose about the origin and ultimate fate of the universe, plus some entropy notions about black holes. I will say this: Hawking throws equations out there like you flat out know what he's talking about. His disclaimer is that he assumes you know some math and quantum mechanics. The QM arguments were easy enough, and while I've seen some topology before, I wasn't hugely familiar with GR, so his essays were sometimes hard to follow.
I thought Penrose's essays were a lot more accessible. Not good. Notes from a Cambridge series of lectures. Terms are not explained. Equations are not explained. Familiarity with 4 spheres, deSitter spacetime, Euclideanization of spacetime is assumed. Jun 04, Hayley rated it liked it. As much as I enjoyed the concepts that were meticulously laid out in this book; it hurt to read. The book required a lot from the reader to understand and keep up with the complex theories, unless of course you brought along your PHD in experimental physics and cosmology, which I did not.
Nov 14, Kim Zinkowski rated it liked it.
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Dec 05, Bob marked it as to-read Shelves: physics , einstein-and-beyond , 0-library. I am not sure how some read this book, but as an undergrad physics student, all I could read are the first couple of pages before the 1st equations. Aug 08, Faith rated it liked it Shelves: temporary-on-hold. Jan 03, Erickson rated it it was amazing Shelves: relativity-theory , quantum-theory , mathematical-physics. Extremely nice and clear book. It may be better especially if one knows well about the subject matter, as it is written more in debate format.
Jun 05, Rodion Krivoshein rated it liked it Shelves: non-fiction , educational. Much more "rocket science" than I can understand. Oct 01, Rachel rated it liked it. Interesting but extremely, extremely confusing. May 01, Joshout rated it it was ok. Very dificult. Nov 15, Peter added it. As I suspected I got less than half of it.
The Nature of Space and Time
But the interplay between Hawking and Penrose playing of each other is amazing. Jan 17, Akshat Tandon rated it it was amazing. I could never understand what's in there! Sep 25, Ewa added it Shelves: science , physics. No stars. I can't rate the book from which the only part I was able to understand was its introduction. Not for the novice! While I was able to follow the broad points, the descriptive mathematics that comprise the majority of the work was well out of my league. Math textbook, here I come Mar 19, Kevin rated it did not like it Shelves: general-science.
Couldn't follow it. Much physics and prior theory is required. Didn't make it through even half of the book. Apr 23, Aubrey rated it really liked it Shelves: read-in-the-past. Full of facts and impeccable research and theory. Reading it is a bit daunting. The language is complex and not very engaging, but there is no question that the material is sound.
Feb 22, Bryan Kornele rated it really liked it Shelves: math-science , Way to much brain power needed to be a recreational read. Interesting and technical in spots. There are no discussion topics on this book yet. Readers also enjoyed. Goodreads is hiring! You might feel a little sad that time travel is science fiction. Something shiny. A golden key. It might not seem like much, but it is.
It goes slower for another reason entirely. Hello Zephir, how are you keeping? So did Schwinger and others.
See the quote by Robert B. Instead the twins paradox is when one twin goes to, say a star at close to light speed. Then he turns around and comes back. The paradox is as follows. Travelling through time in the opposite direction is, according to the laws of physics as currently formulated, science fiction — unless you allow for Quantum Mechanics and the uncertainty principle, where quantum systems can perform time travel tricks, as measured by experiment.
Remember the stasis box. Instead, outside that box, everything else is. Not time travel. What qualifies as time travel is semantics. You say we do not due to the stasis box. The Heisenberg Uncertainty Principle is just a wave thing. Nor do seismic waves in the ground.
And nor do waves in space. We discover time has only mathematical existence, namely, time is numerical order of events which run in space. One can move in space only and not in time. In space is always NOW. One day Amrit, everybody will be on this same page. The page where it starts.
Hi John, here you are now. I always liked your answers in physics. I wonder why they suspended your account. You say the progression of time is intimately linked to the speed of light, agreed! You describe time as motion and compare it to heat and I nearly agree. But while heat depends on the mean-square of the speed of the involved particles, time, i.
Harald: I think it was because my answers were very good, with excellent references. So much so that a resentful cabal saw me as a threat, conspired to downvote , and then suspended me on specious low quality grounds. Not good. But all too common I fear. I am reminded of peer review by Nick Kim : Yes, I think time is straightforward.
It beats me why people make such a big mystery of it. IMHO the important thing is that when you understand time, you understand that the speed of light is not constant. Then with a little light reading of the Einstein digital papers, you understand gravity.
See the other articles. I see there is a plugin for it. PPS: Mathjax installed! Folglich—ist Philosophie ein Laster? And that William Kingdon Clifford more or less nailed it with his space theory of matter. This is where it starts, with time. After you understand that, you understand that the speed of light is not constant, then you can understand gravity. Then when you understand that a gravitational field is not curved space, you ask yourself what is?
My point is that the scientist should be empirical, and not allow himself to be distracted by abstraction. Philosophy is not a vice. Ask any physicist with a PhD. I can show you time; but it is directly pointing away, when I show it, in the line of sight; you look through the dimension, rather than onto it, when looking into deep space. There: you have it! The taste for expressing everything in terms of math-formula is that of a fearful kid who cannot cope with the world.
If there ever was a generral study on mathematicians, shyness, reluctance to act, proneness to precaution-measures that others would deem ridiculous — I am sure such study would find some great trend in said flock of people. But I am esp. Sorry, again, for asking ignorant questions…. Something that is 0, cannot be multiplied to be anything but 0. There are two papers of his strongly linked together, one heralding the other I read very recently, that got me intrigued; esp. I mean this: arxiv. Well… you kind of are, as you have to turn to and turn away from, the thing you try to explain away in order to explain it away.
So — you ARE?! Time is not one of the 3 dimensions we can directly observe, in a still-frame. I cannot hop forward a second as much as I cannot quantify a feeling, touch the wind or eat a thought or — whatever! I cannot vacate the total space I am occupying yeah yeah; I can lose some weight; stop pressuring me! You are hear and now, for that split of a second. Facts are pesky to communicate; all encompassing philosophical principles, however, can be bullet-proof, like religious believes… Now, on a serious note: that idea is both self-consistent and flawed.
Any attempt to freeze a person will ultimately destroy pretty much all the cells in his body, as the water freezes, and ice-crystals rip open the cellular walls… good luck with waking up with that! Or Daedalus…. Hawking … he wrote so himself I may be paraphrasing , in one of his books.
I see scifi for what it is: science-fiction! If you actually did read it, though, I still hope you can take something away from it, non-the-less. As I was actually meaning well, with constructive criticism, on some of the introductory arguments you gave… PS: I enjoyed the bottom third much more than the other parts…. Or did you manually erase it? Perish the thought! Your last reply went into the bin. Anyway, I have now restored it. Yes, the height gives the Lorentz factor. Re electron spin, think of a helical spring.
When you stretch it out, from the side it looks like the zigzag path of the parallel-mirror light beam. Imagine you can watch the zigzagging light beam through a telescope which is panning from left to right. In your field of view you see the light beam moving straight up and down at a slower rate. We live in a world of space and motion, not in some 4D spacetime. You can feel the air blowing in your face. Sorry, but I meant what I said about being distracted by abstraction. Yes, I value thinking for oneself and understanding in-depth. See this. IMHO the driving force is beauty, not fear.
See the monopole article, which I posted today. Yes, the time dimension is different because time is a dimension in the sense of measure, not in the sense of freedom of movement. I can move in the space dimensions. As for feelings and thoughts, they are qualia. Spacetime models space at all times. The past is the name we use for the state of the universe prior to things moving to their current location.
People are very good at being foolish, especially when they are convinced they are somehow superior. What idea is both self-consistent and flawed? I am not a fan of Hawking radiation. I share your sentiment re length contraction. In fact I would say fast moving objects get lengthened, not shortened. Check out muon decay.
Muons last longer when they move fast. Yes, freezing adults is science fiction. So is uploading your mind into a computer. A copy is not you, just as your twin is not you. Yes, a solution might have no basis in reality. I have previously used the example of a negative carpet measuring -4m x -4m. Wait until you read what I say about Hawking radiation. You will be pleased.
The Nature of Space and Time - Wikipedia
As for the last third, try reading it all again, in a week. One cannot answer what one did not pay attention to. If I did not make myself clear, I am sorry, non the less. For I am suspecting, more and more, that it is not. In terms of gravity you already concede that — but in terms of special relativity, the opposite was suddenly true.
So, as a pyrrhonean I am having my doubts, non the less. As I do about dark energy and dark matter, the phologistons of our day and age. And Hawking-radiation… Have a good one! But cross my heart and hope to die, I read through your comments carefully, step by step. Newton and Einstein proposed no theory of space or of time. Their theories only proposed a way of transforming from one coordinate frame to another. For all anyone should care, they were both simple geometers. But I would say the most important aspect of this means of measurement is the concept of wave and particle, they are diametrically conjugate aspects of the one theory.
This concept is not true. There are only waves… particles are an abstraction whose limits are absurd contradictions of real world physical measurement theory. The most fundamental principle are not those of Einstein or even Newton but the Quantum Principle, the quanta is a packet, to deal with quanta as particles is entirely incorrect.
Waves have a near field and a far field region and there is a gradation between the two called the Fresnel region. Everything is fine as long as the distance between points is greater than the Fundamental Resolution Limit 0f The Theory. This limit in nature is the quanta. It is legitimate to measure to smaller dimensions that the size of quanta, but it will produce incorrect results in the Near Field Evanescent Field.
The underlying theory of everything is a quantum theory. This is an undisputed truth, a point of truth that this discussion has not addressed. Current Mathematical Pedantism admits nothing within the near field limit for ideal point particles. Testing a string theory whose basic limiting features are those of quantum theory is the correct approach. Of course it will not advance until this artifice of dressing strings with particles, as if they were baubles on a Xmas Tree, is fully understood to be a load of you know what.
I could show you a thousand experiments which show this ideology or outright belief of strings is incorrect because the limiting case of String Theory is not Quantum Theory and Quantum Theory is not the current limiting case of String Theory. The false logic begins with the definition of particles. There is really only one kind of mathematical particles, the point particle, all other systems of particles are not true particles but extended objects.
It does this by having a Speed Of Light SOL defined Internationally to be not actually being a fixed number of meters per second not rounded off… but an exact number. While defining the SOL to be that accurate is a fine thing but when it comes to errors… the errors begin to occur when you measure distances less than a meter where the speed of light varies in the near field while traversing to the far field….
This has been determined in the laboratory. Electromagnetic forces in the near field are defined by the virtual photons to be found there. This is what is known as the Equivalence Principle. The way of showing that these two different scenarios are in fact the same goes as follows:. First, we identify two frames of reference that we will carry out experiments in.
These situations will be in a ship both in open space and on the surface of Earth with a gravitational force the acceleration due to gravity being 9. With you in the ship is a ball and a small hole in the wall. First consider the ship on Earth experiencing gravity. You would feel yourself pressed to the floor of the ship and if you picked up the ball and let it go, you would observe the ball fall to the floor at a rate of 9.
With an idea similar to this in mind, Einstein claimed that the effects of gravity and acceleration were the same thing. This was a crucial step in furthering our understanding of gravity, light, and time. Now we turn our attention to the small hole in the wall of the ship. From outside, a pulse of light from a laser flashes through the hole. While you are in open space and not accelerating, this beam of light would travel in a straight line across the ship and impact the wall directly opposite of the hole. To you in the ship, the light would appear to bend downwards in the presence of the accelerated frame of reference.
Now recall what we already established with the Equivalence Principle and the ball drop experiment.
http://derivid.route1.com/refugio-crnicas-del-nuevo-mundo-n.php Someone in a ship in open space accelerating upwards at a rate of 9. But is this true? Does light actually bend when in the presence of a gravitating body? The short answer is yes, but to establish why we must first discuss space and time, and how they are intimately linked. Einstein truly was a man beyond his time; his mind was able to reach out of the known and visualize what nobody else had. But how can we visualize this to help with understanding this amazing discovery?
The most useful way that I visualize spacetime and how it interacts in such a way as to produce the bending of light is with yet another thought experiment. Now, imagine the rubber sheet is pulled tight at the edges; this is spacetime. Without anything on it, it is flat. Have your friend stand opposite of you and then take the marble and roll it towards them; the marble representing a photon. What your friend observes is the marble rolling to them in a straight line. Now, place the heavy ball in the center of the sheet; the ball being a massive body like the earth or the sun.
What you and your friend observe is the ball sinking down into the sheet and creating a sort of well; this well is what we experience as gravity! If you roll the marble sufficiently fast enough, it will dip into the well, roll around the inner well wall a bit, and then up and out of the well. Depending on how fast you rolled the marble, or how deep the well is, will affect where the marble exits the other side.
The marble will have deflected onto a new trajectory. Keeping this visual in mind, you can now somewhat grasp how light would appear to bend in the presence of gravity! For the light, it is traveling in a straight line, but if spacetime itself is curved the light will follow that curvature. The Earth is huge and so light should be bending all around us! But it is such a small deviation that it goes unnoticed.
Think back to the scenario presented with the sheet: depending on how fast the marble was rolling, or how deep the well was, this would determine where the marble exits the well. Meaning that the only thing that determines how much the light is deflected by as seen by an observer like your friend is how deep the well is in spacetime called a gravity well that the light interacts with.
Since light is so fast, you would need an incredibly deep gravity well to notice this curvature. This is exactly what Einstein knew when he postulated this idea. He knew that he would need something with much more mass than the Earth to ever be able to see light bend with the technology he had available at that time. He recognized that our sun would have sufficient mass to produce a gravity well deep enough to create a noticeable deflection of light.
And what would be supplying the light to be measured? Distant stars. But the only way to actually image stars around the sun was during a total solar eclipse. For this, he turned to the astronomer Sir Arthur Eddington. Einstein was correct in his view of how gravity and light interacted.
I talked of dilation calculations and contraction values. Up until the early s, physics was dominated by two very big ideas. These ideas came from Isaac Newton and James Maxwell.
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Isaac Newton, when forming his theory on gravity and motion, stated that time and space were absolute and unchanging for all observers. At the beginning of his seminal paper, Principia Mathematica, he defined time to pass equally for all things and essentially to be invariant to all ways of measuring it.
Likewise, he also defined space to be immovable and unchangeable; an absolute to measure positions against. These were crucial definitions when forming his mathematical treatments for how massive bodies interacted gravitationally. James Maxwell, often referred to as the father of electromagnetic theory and one of the most important natural philosphers to have ever lived, developed the mathematical framework that describes how electricicy and magnetism behaves.
His approach involved modeling both of these physical systems using fields that interacted with each other in intrinsic ways, showing that they were both a part of the same process. One of the products of these interactions was something he called electromagnetic waves, and in studying them he discovered something amazing. The velocity of these waves were exactly what we measured the speed of light to be: approximately ,, million mph. This was no coincidence, and he later went on to prove that light itself was an electromagnetic wave.
A curious consequence of how his mathematical laws worked implied that light traveled at only one speed regardless of relative motion. This was a direct contradiction with Newtonian physics which stated that velocities of objects being measured added and subtracted dependent on their relative motion. Despite this discrepancy between these two leading theories being known, it would take a genius to work out a way to either reconcile the two, or to declare one the victor and reside the other to defeat.
To elucidate the issue between these two theories, I will use a thought experiment developed by Einstein and illustrated in his work describing Special Relativity. Imagine two friends, one named X and the other Y. Y is standing at a train station during a thunderstorm and X is on the train.
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