Size and Scale
Flying bumblebees violate the laws of physics! Who hasnt heard someone say this at one time or another? People may marvel that mosquitoes can walk on water, flies stick to the ceiling, or that cats can jump several times their length. Such talents seem supernatural to those who do not understand physics.
The simple explanation for these feats is that physics is not the same at all scales. The laws of physics changeor rather, certain physical forces dominate over othersdepending on the size of the object and what scale defines its domain.
Most interestingly, some of the problems physicists are now encountering in quantum physics derive from the size and scale issue. Physicists frequently make the mistake of applying imagery from the macro-world to the subatomic world. Difficulties occur when we attempt to measure quantum events at a classical physics scale, as we will discover in the Quantum Physics section in this chapter.
Different forces dominate these two objects.
The table below may help you to understand these size-scale relationships:
Orders of Magnitude
Classical Newtonian high school physics describes a universe of mostly empty space, peppered with atoms arranged into mechanistic systems. This Common Universal Modela void containing atoms mimicking a planetary system (electrons orbiting a central nucleus as planets orbit a star) seems, intuitively, to serve well as an adequate and logical model of reality.
It is, however, abysmally simplistic and mostly wrong,
Newtonian physics implies that the universe is populated with only non-sentient objects. Scientists of Newtons era believed that there was some force separate from the forces acting on material objectsan omniscience or omnipotencethat exists as first cause of everything, a creator. Life, and especially humankind, was therefore not subject to the physical laws of the rest of the universe.
Newtons Laws of Motion apply to large objects; these physical principles become insignificant for very small objects because other physical forces dominate smaller objects.
While Newtons Laws of Motion are still an accurate description of how large objects move in space, these laws are by no means a complete representation of how everything behaves in the universe. As we venture further into particle physics and cosmology, the most important concept to understand is that regardless of what we are discussing or how we describe it, we must always consider its relationship to all other things. Though science often employs reductionism in its pursuit of truth, the idea of relationship must never be forgotten or dismissed.
Relationship is at the heart of understanding energy and matter, and space and time. It is not possible to discuss energy without invoking mass (how much matter is present), or to discuss space without invoking time (as both are a measure of distance).
What is space made of? Democritus argued for nothingness, while Aristotle rejected the notion of emptiness in favor of somethinga background medium he called the plenum. James Clerk Maxwell argued for the existence of the ether. Einstein was the first to postulate that the mechanical properties of spacetime are determined by matter/energy (as matter and energy are equivocal: E = mc2). Matter curves spacetime; this curvature is dependent on the distribution of matter (mass) within space.
Gravity is the weakest force
in the universe, yet is by far the most long-reachingit
is infinite. Gravitys domain includes everything in the
universe, but its effects are significant only for things larger
Mass curves space in three dimensions.
Gravity and accelerated motion are equivalents as matter and energy are equals. Gravity and acceleration both curve space. The geometry of space and gravitational force are therefore equal. In the words of physicist John Wheeler: Mass grips spacetime, telling it how to curve; spacetime grips mass, telling it how to move.
In classical physics, time is a measurement of motion in space. Time is regarded primarily as a fourth dimension, an effect of an expanding universe, which is revealed as entropy, the tendency of a system to go from order (symmetry) to disorder (asymmetry). Entropy may also be described as an ultimate state of inert uniformity. Entropy within a closed system must increase with time. Entropy is what causes the contents of a glass to reach a uniform temperature when ice cubes melt in room-temperature water. Entropy is loss of energyspecifically, heat. Everything loses heat. Energy must be pumped back into a system to equalize this lossthis does not happen in a closed system. Since the universe is a closed system, it has been losing heat since the Big Bang. From a trillion degrees Fahrenheit, it has cooled to 2.7 degrees Kelvin in about 15 billion years. The remaining background radiation in the universe is in the microwave range.
Times arrow has only one directionoutward from the initial singularity explosion and inflation known as the Big Bangso humans perceive that time passes. This is the perception of a linear mind, a mind able to understand only sequential reality.
Entropy is the way we measure time passing or rather, it is the way we used to measure it. Our concept of time has matured, as we will see later.
Time is relativemeaning that it is not a constant, is not the same for everyone at every place in the universe. Velocity changes the experience of time as well as that of space. Increased velocity expands time, which contracts and condenses space; decreased velocity contracts time, which expands space. From a spaceship, for example, the universe looks huge and infinite at low speeds. Bring that spaceships velocity up to near-light speed and a peculiar thing happens: The faster we go, the more contracted our view of the universe becomes until all the stars seem to squeeze to a pinpoint at the center of a long black tunnel.
This is in direct conflict with popular science-fiction movie depictions of warping into light-speed and watching all the stars streak outwards from our direction of travel. It is wrong. (And so are those noisy explosions in space we have all come to expect in the movies. Sound does not travel without an atmosphere as a medium. It is air molecules colliding into each other that creates sound.) In summary:
As we will discover, classical physics is woefully incomplete and inadequate in describing spacetime. Quantum physics has shed new light on spacetime, gravity, and the special theory of relativity.
In classical physics, matter is simply whatever is not space. Mass is how much matter is in an object. Mass does not mean weightweight changes with the gravitational field in which the matter resides; mass does not. In addition, energy and matter are interchangeable entitiesthey are identical. Remember E = mc2? Einsteins famous equation literally means that energy is the same as mass multiplied by ceritas (the speed of light) squared. As a result, in physics the mass of a particle is measured in electron voltsan energy measurement. (See tables 4.d and 4.e on p. 94.)
Also according to Einstein, an accelerating object increases in mass due to the increase in energy from the acceleration (mass and energy being equals, as in E = mc2). This increase in mass would increase its energy requirement to maintain momentum. (Momentum is the result of mass times velocity, in which velocity is defined as the derivative of position with respect to time.) This is why it is currently not possible to even approach the speed of light in space travel.
Remarkably, matter is 90% or more empty space. If all space were eliminated from the atoms that make up a human being, the mass volume would be the size of a pinhead.
Mass is partially an effect of atomic movement. The more confined in space a particle is, the faster it moves. Things are perceived as solid when electrons spin at least 600 miles per second. Consequently, there is no such thing as a solid in the subatomic realm; solidity is significant only on scales above the molecular realm.
Thermodynamics is the study of the interrelation between heat, work, and the internal potential energy (mass) of a system.
In classical physics, atoms contain many subatomic particles with specific properties. Some particles are stable and some are not. Stable particles include protons, neutrons, electrons, photons, and neutrinos. Theyre around all the time and generally dont change into other particles unless exposed to unusual extremes. Stable particles are sometimes called hadronswhich include the sub-classes baryons and mesons; and leptonswhich include electrons and neutrinos. More on this strange zoo in the Quantum Physics section.
Electrons rule the atom: It is the exchange and sharing of electrons that governs how atoms bond together to form molecules, and eventually, complex material systems.
Electrons obey strict rules of behavior in some instances, and in other instances seem to behave arbitrarily, tunneling through domains and barriers like crazed escape artists (this property of electrons is discussed more in-depth in the Quantum Bizarro section). Inside the atom, electrons maintain their own territorial energy levels (or states) called shells and cant collapse into each other. This is called the Pauli Exclusion Principle and cannot be violated. The number of electrons in the outermost shell determines atomic stability. In general, the innermost shell (shell 1 or the s shell) of an atom contains two electrons (except in hydrogen). Subsequent shells contain a number of electrons dictated by the formula 2n2 (n = the shell number).
Atoms also obey the Octet Rule, meaning that if the outermost shell of an atom contains eight electrons it is fairly stable. Atoms will combine readily with other elements that have a complimetary number of electrons in their outer shells. This is determined by valence, the number of electrons atoms will share with other elements to complete the octet. Valence is equal to the number of outer electrons if four or less; otherwise, valence is equal to 8 minus the number of outer electrons.
For example, sodium (Na+) contains one electron in its outer shell (valence +1); chlorine (Cl) contains seven (valence -1). These two elements readily combine to make up sodium chloride (NaCl).
There are four forces in the universe: electromagnetic, strong nuclear, and weak nuclear, and gravitywhich may not be a force at all according to Einsteins original thesis. (More on gravitys paradox later in the Quantum Physics section.)
Before the Big Bang (when the universe was born), all forces were unified into one. Scientists are putting it all on the line to accelerate particles at high enough energies to reunify the forces into one. This pursuit is the Holy Grail of particle physics, and will result in a Grand Unified Theory (GUT).
To date, two of the forces have been unified: The electromagnetic and weak forces are known collectively as the electro-weak force. Physicists are trying to collide particles in synchrotrons and cyclotrons (particle accelerators or colliders) at high enough speeds to unite the strong and electro-weak forces. Such a breakthrough would bring us closer to an understanding of how the universe formed.
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