So why would you have to multiply the mass of that walnut by the speed of light to determine how much energy is bound up inside it? The reason is that whenever you convert part of a walnut or any other piece of matter to pure energy, the resulting energy is by definition moving at the speed of light. Why, then, do you have to square the speed of light? It has to do with the nature of energy. When something is moving four times as fast as something else, it doesn't have four times the energy but rather 16 times the energy—in other words, that figure is squared.
So the speed of light squared is the conversion factor that decides just how much energy lies within a walnut or any other chunk of matter. It will continue to reflect like this, with the box moving towards one side half the time, and remaining stationary for the other half of the time. The energy of a photon depends on the wavelength it has; longer wavelength are lower in energy and Image credit: Wikimedia Commons user maxhurtz.
Now, the photon collides with the box, and is temporarily absorbed. Energy and momentum of the box, post-absorption. If the box does not gain mass from this So far, so good, right? Only now, we can look at the box, and ask ourselves what its energy is. Is this a crisis of some sort? Once the box absorbs the photon, its mass is different and increased from what it was before it interacted with the photon.
After the wall of the box re-emits a photon, momentum and energy must still both be conserved. Mass-energy conversion, with values. This is a BETA experience. You may opt-out by clicking here. More From Forbes. Jul 23, , am EDT. Jul 15, , am EDT. Jul 8, , am EDT. The time component of the momentum vector in 4D space is mc , mass times the universal speed limit.
Momentum is a conserved quantity as is mass which is equivalent to energy. Mass and energy are different manifestations of a single underlying physical quantity. Energy, mass and momentum form a spacetime object known as the energy-momentum four-vector.
The details are in the book. The foregoing is just intended to give the flavor and flow of the book. The second half of the book is easier to digest as Cox and Forshaw give a broad overview of assorted physics topics. They describe the vast amount of energy in a tiny amount of mass and how that mass is converted, not just in nuclear reactions but in chemical reactions and other everyday phenomena. The authors discuss the Higgs boson as the origin of mass, even though this was just a prediction when they wrote the book.
They even go back to the Big Bang and the disparity between matter and anti-matter. They then present the equation for the Standard Model, explaining what each term represents. They discuss how the model was put together and the various contributors, Glashow, Weinberg, Salam, Feynman, and Gell-Mann.
Finally such a wide ranging review would not be complete without General Relativity to which the last chapter is devoted. I enjoyed this book.
However the presentation was a bit disjointed. The authors write for readers at varying levels bouncing back and forth between simple explanations and more difficult detailed ones. They insert apologies to those for who the material might be too complicated and for those who might get bored. While the math itself was not overly difficult, following it in terms of the concepts it represented was more demanding. Still I applaud the effort to put some accessible math behind concepts that are deep and not intuitive.
Regardless of level this is a book for a non-scientist reader with a strong interest in the subject. Cox and Forshaw said the book was meant to be a challenge. It was and that made it worthwhile. I was expecting, from the first few paragraphs of the book, that I was going to breeze right through this. It didn't really happen that way. I had to take college physics, which included the basics of relativity and quantum theories, so I probably have a bit more knowledge than the average non-physicist.
All the same, there were areas of this book that just did not seem to click at all, even after reading paragraphs over and over again. Usually the parts that didn't click were the "easy" examples such as how the distance between the moon and the Earth get further apart as the spin of the Earth slows. For anyone that doesn't know about conservation of rotational momentum, this is not an easy thing to figure out.
Especially since they don't even mention momentum until 5 chapters later. The end of the book definitely seemed a little bit rushed, mainly due to the "just take our word for it" approach for what they deemed hard to understand topics.
I understand this was attempting to make Einstein's theories accessible to lay people, but I feel it felt a little bit short. I would love to say that I understood every word and every example of this book, but unfortunately there were many times I felt like the concepts were far too complicated for me. I'm not an unintelligent person but my math and physics knowledge is rather old and rusty. I'll give it another 2 or 3 read through before making any firm judgements on the books.
I feel I have learned something from this book I just don't know what it is I've learned.. Absolutely senseless. If he ever gets close to talking about the matter at hand, another long passage about a motorcyclist will pop up to "explain things" Look.
The reason you use so many horrible analogies is because you are a horrible explainer! Convey it the first time, don't waddle about. On a good day, high school physics class used to leave me feeling kind of for lack of a better word high. This book brought back that old, familiar feeling, but in an even better way. In the end, I walked away with a much clearer understanding of Einstein's theories of special and general relativity than I ever achieved slogging through high school physics.
I think our teacher must have been unable to articulate and synthesize the underlying questions that the equations sought to answer. This process is broken down into a few key steps: 1 an understanding that the speed of light is constant and therefore space and time must be "variables"; 2 the mathematical definition of spacetime and the formula needed to relate events within it; and 3 the definition of vectors in spacetime.
It really is as simple as that. With an understanding of these key relationships, the elegance, beauty, and profound repercussions of the equation become crystal clear, even for those of us who never pursued physics beyond high school. I did struggle with a few sections, particularly the bits about electromagnetism, the conservation of rotational momentum, and--I hate to say it--the "tiny physicists in elevators" analogy.
In spite of my mushy understanding of those parts, I was still able to "go there" with the authors in the end. The English major in me was a little miffed when they had a go at Murray Gell-Mann for taking his inspiration for the name "quark" from Finnegan's Wake , but otherwise I enjoyed the authors' playful, easygoing tone.
You should.
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