Quotes About Physics

The equations are indifferent to the supposed freedom of human will. Some have taken this to mean that in a classical universe, free will would be an illusion. You are made of a collection of particles, so if the laws of classical physics could determine everything about your particles at any moment—where they'd be, how they'd be moving and so on—your willful ability to determine your own actions would appear fully compromised.

They imply that a region of space the size of a pea would be stretched larger than the observable universe in a time interval so short that the blink of an eye would overestimate it by a factor larger than a million billion billion billion.

Dutifully following the second law, we conclude that today's state derives from yesterday's even lower entropy state. And that state, we envision, derives from the day-before-yesterday's still lower entropy state, and so on, yielding a trail of ever-decreasing entropy taking us ever farther back in time until we finally reach the big bang.

If free will is an illusion, and if time travel to the past is possible, then your inability to prevent your parents from meeting poses no puzzle. Although you feel as if you have control over your actions, the laws of physics are really pulling the strings.

Physicists traced the failure to the jitters of quantum uncertainty. Mathematical techniques had been developed for analyzing the jitters of the strong, weak, and electromagnetic fields, but when the same methods were applied to the gravitational field-a field that governs the curvature of spacetime itself-they proved ineffective. This left the mathematics saturated with inconsistencies such as infinite probabilities.

Remember from Chapter 7 that in the Many Worlds framework, every potential outcome embodied in a quantum wavefunction—a particle's spinning this way or that, another particle's being here or there—is realized in its own separate, parallel universe. The universe we're aware of at any given moment is but one of an infinite number in which every possible evolution allowed by quantum physics is separately realized.

The studies concluded that the graviton must be massless and chargeless, and must have the quantum mechanical property known as spin-2. (Very roughly, the graviton should spin like a top, twice as fast as the spin of a photon.)

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Special relativity declares a similar law for all motion: the combined speed of any object's motion through space and its motion through time is always precisely equal to the speed of light.

The uncertainty principle establishes that regardless of what equipment you use or what techniques you employ, if you increase the resolution of your measurement of one property, there is an unavoidable cost: you necessarily reduce how accurately you can measure a complementary property. As a prime example, the uncertainty principle shows that the more accurately you measure an object's position, the less accurately you can measure its speed, and vice versa.

Now, from special relativity we know that energy and mass are two sides of the same coin: Greater energy means greater mass, and vice versa. Thus, according to string theory, the mass of an elementary particle is determined by the energy of the vibrational pattern of its internal string. Heavier particles have internal strings that vibrate more energetically, while lighter particles have internal strings that vibrate less energetically.

No deviations from the predictions of general relativity have been found in experiments performed with our present level of technology.

Then, just as two trees are the same age if they have the same number of tree rings, and just as two samples of glacial sediment are the same age if they have the same percentage of radioactive carbon, two locations in space are passing through the same moment in time when they have the same value of the inflaton field. That's how we set and synchronize clocks in our bubble universe.

so, with only finitely many different particle arrangements, the arrangements of particles within patches must be duplicated an infinite number of times. That's the result we've been after.

Solving problems, learning how the universe is put together-that's what had always captivated me.

By shaping our intuition and developing our cognitive skills, evolution initiated our education in physics but our more comprehensive understanding has emerged from the force of human curiosity expressed through the language of mathematics.

turn the earth into a black hole you'd need to squeeze it down to about two centimeters across;

If we envision that, somehow, the surface area of a black hole is a measure of the entropy it contains, then the increase in total surface area could be read as an increase in total entropy.

It doesn't seem that something on a hard-to-locate boundary is somehow calling the shots regarding what happens here in the bulk.

The uncertainty principle tells us that the universe is a frenetic place when examined on smaller and smaller distances and shorter and shorter time scales.

At the ultramicroscopic level, the universe would be akin to a string symphony vibrating matter into existence.

Notice that the value of the entropy and the amount of hidden information are equal. That's no accident. The number of possible heads-tails rearrangements is the number of possible answers to the 1,000 questions-(yes,yes,no,no,yes,...) or (yes,no,yes,yes,no,...) or (no,yes,no,no,no,...), and so on-namely, 2^1000. With entropy defined as the logarithm of the number of such rearrangements-1,000 in this case-entropy is the number of yes-no questions any one such sequence answers.

But the gravitational attraction between two smaller things, like two electrons, is a million billion billion billion billion times weaker than their electromagnetic repulsion.

As the amount of matter used to create a black hole increases, the required density to which that matter must be crushed decreases.