Religion in an Age of Science by Ian Barbour
Chapter 4: Physics and Metaphysics
II. Relativity and Thermodynamics
1. Space, Time and, Matter
expressions of the underlying implicate order.22
Bohm’s scheme shows a dramatic wholeness by allowing for nonlocal, noncausal, instantaneous connections. Events separated in space and time are correlated because they are unfolded from the same implicate order, but there is no direct causal connection between them since one event does not itself influence another event. It is like two TV screens showing images of a moving object taken from different angles; the two images are correlated, but one image does not influence the other. The scheme does not violate the relativistic prohibition of signals faster than the speed of light, for there is no way to use it to send a signal from one detector to the other. (We can not control the orientation of particle A, which arrives at random. The statistical correlation only shows up in the later comparison of the records from the two detectors.)23
Most physicists acknowledge that Bohm’s view is consistent with these experiments, but they are reluctant to abandon Bohr’s view until there is experimental evidence against it. The development of quantum potential theory by Bohm and his coworkers may lead to distinctive testable predictions, but it has not done so to date.
In sum, Einstein’s classically realist, determinist, and local interpretation seems to be ruled out by the Aspect experiments. Bohm’s theory, with Its classical realism, determinism, and extreme nonlocal holism, cannot yet be experimentally distinguished from standard quantum theory. The instrumentalists claim that we cannot say anything about the world between observations and therefore questions about determinism and holism should be dismissed as meaningless. I have advocated a
combination of critical realism, indeterminacy, and a more limited form of holism, and I have suggested that Bohr himself was closer to this view than to instrumentalism.
For Newton and throughout classical physics, space and time are
separable and absolute. Space is like an empty container in which every object has a definite location. Time passes uniformly and universally, the same for all observers. The cosmos consists of the total of all such objects in space at the present moment, which is a simultaneous and shared "now." The length and mass of an object are unchanging,
intrinsic, objective properties, independent of the observer. All of this is close to our everyday experience and common-sense assumptions, but it is challenged by relativity.
In 1905, at the age of twenty-six, Einstein wrote his first paper
proposing special relativity. The search for symmetry in the equations for moving electromagnetic fields, along with the Michaelson-Morley experiments with light, led him to postulate the constancy of the velocity of light for all observers. This hypothesis had unexpected and far-
reaching implications. Imagine that an observer at the middle of a moving railway train sends light signals, which reach the equidistant front and rear of the train at the same instant. For an observer on the ground, the signals travel different distances to the two ends (since the train moves while the signals are traveling); therefore if the signals travel at constant velocity in his framework they must arrive at different times. The two events are simultaneous in one frame of reference but not in the other. The effect would be very small with a train but would be large with a space rocket or a high-energy particle approaching the velocity of light.24
There is also a time dilation, which has been confirmed in many experiments. For example, a mu-meson has a lifetime of 2
microseconds. But if it is traveling at very high velocity in a circular orbit in an accelerator, its lifetime as measured on the ground will be much longer, and it will go around many more times than one would expect. Measurements of mass and length as well as time vary according to the frame of reference. The mass of a particle, such as the circulating meson, becomes much larger as its velocity relative to the measuring apparatus approaches the velocity of light. Lengths contract, so a moving object appears much shorter in the direction of motion (though from the moving object, it is the other objects that appear compressed).
The theory also predicts the equivalence of mass and energy (E = mc2, confirmed in the atomic bomb explosion), and also the creation and annihilation of matter and antimatter (confirmed in the creation and mutual annihilation of electron-positron pairs).
Because there is no universal simultaneity and no common present separating past and future, the division between past and future will vary among observers. Some events, which are past for one observer, may still be future for other observers. However, for any two events that could be causally connected (a light signal could pass between them), the order of before and after is the same for all possible observers. No one could conclude that an effect preceded its cause. There is no way to influence the past or to change history. People could leave the earth on a spaceship in the year 2000, travel at high velocity for five years, and return to earth five years older to find themselves in the year 3000. But there is no way they can go back to the year 1000. ("Time travel" works only in one direction, so no one will face the science fiction question of what would happen if you went back and killed one of your ancestors.) Space and time, then, are not independent but are united in a spacetime continuum. The spatial separation of two events varies according to the observer, and the temporal separation also varies, but the two variations are correlated in a definite way. Different observers "project" spatial and temporal dimensions of the four-dimensional spatiotemporal interval in different ways, but each can calculate what the other will be observing.
There are rules for translating into equivalent relationships in another frame of reference.
In 1915, Einstein went on to develop the general theory of relativity, extending his earlier ideas to include gravity. He reasoned that an
observer in a windowless elevator or spaceship cannot tell the effects of a gravitational field from the effects of accelerated motion. From this he concluded that the geometry of space is itself affected by matter.
Gravity bends space, giving it a four-dimensional curvature (here the fourth dimension is spatial rather than temporal, and it is reflected in the altered geometry of three-dimensional space). As John Wheeler puts it,
"Space tells matter how to move, and matter tells space how to curve."25 Dramatic confirmation was obtained in 1919, when it was observed during an eclipse that light rays from distant stars were slightly bent by the sun’s gravitational field. Time is also shrunk by gravity, and clocks slow down as they do from relative motion. In 1959, very accurate experiments at Harvard showed that a photon traveling from the basement of a building to the top floor changes its frequency slightly because of the difference in gravitational field.
One of the most striking conclusions from general relativity is that the universe may be finite, curved, and unbounded (that is, closed) rather
than infinite (that is, open). If so, a person setting out from the earth into space in one direction would return eventually from the opposite
direction. As we will see in the next chapter, it is not clear from present evidence whether there is sufficient matter in the universe for space to be closed rather than open. But what has been clear since Hubble’s red- shift measurements is that space itself is everywhere expanding. The present motion indicates the expansion of all parts of the universe from a common explosion 15 billion years ago. This was not the explosion of matter into a preexisting void, but the expansion of space itself.