We are accustomed to think of the universe as a collection of objects of various sizes. And we tend to think that each object has certain properties, properties that are independent of the other objects. In fact, the very word object implies something that is disconnected from the observer and from other objects. An object has properties like mass, volume, position, and temperature.
But what does this mean, when we say an object HAS properties? If we take away all of its properties, mass, volume, position, and so on, what’s left? Nothing. A so-called “object” that has no mass, no volume, and no position is not an object at all. It doesn’t exist. So saying that an object “has” properties is actually incorrect. What we should be saying is that an object is a collection of properties. These properties, or observables, are what we actually measure or perceive. They are what, collectively, we call existence.
Take mass for example. An object has mass, and this never changes, as long as the object itself doesn’t change. Right?
The problem with this is that it simply isn’t true. The mass of an object depends on its relationship to the measuring device. If we measure the mass of an object that is moving at a high speed in relation to us, we get a very different reading than if we measure its mass when it is merely sitting next to us.
Einstein taught us that mass and energy are interchangeable. In principle, every piece of matter in the universe could be converted into energy. Energy, like mass, is relative. An object doesn’t have ONE energy. It has an infinite number of them. It all depends on what we are measuring in relation to. Let’s take kinetic energy for example. Kinetic energy is a function of the mass and velocity of the object. But velocity is relative. If I’m driving down the road at 60 mph with my wife in the passenger seat, my velocity relative to her is zero. My velocity relative to a deer standing in the road is 60 mph. My velocity relative to another car approaching at 60 mph is 120 mph. So my kinetic energy will naturally depend on which of these objects I am measuring it in relation to. That is not some vague theory. It translates into inescapable reality, as I will discover if I hit the deer or the other car.
The same kind of issue exists with potential energy. Let’s say I’m standing on a platform 100 feet above the ground. My potential energy relative to the ground is one value. But in relation to someone standing on a platform 50 feet below me, it’s half of that. In relation to someone standing on a platform 25 feet below me, a quarter of that. And if there’s a hole in the ground below me, with someone standing in it 200 feet below me, my potential energy in relation to them is double that.
What about heat? Surely heat energy is intrinsic to an object. Well, heat energy is only meaningful when we specify what we are measuring it in relation to. The only reason a steam engine works is that the steam is hotter than its surroundings. If an object is the same temperature as its surroundings, no work can be performed, therefore there is no energy. Only if the heat can be transferred to a cooler system does it make sense to speak of heat energy. If every chunk of the universe was at the same temperature, there would be no talk of heat energy.
Energy, broadly defined, is the “capacity to do work.” But work can only be performed by one system or object on another system or object. Energy is an expression of relationships, not intrinsic properties. The same is true of any other measurable quantity. In retrospect, this shouldn’t surprise us, because EVERY MEASUREMENT IS A RELATIONSHIP between the system being measured and the system doing the measuring. In quantum mechanics, we would say that the two systems are entangled.
My point is that we can’t meaningfully speak of an object as having a measurable physical state except as it relates to other objects. So-called physical reality is relational. This is a tough pill to swallow for many of us, because we tend to see the universe as a collection of independent objects, made of some kind of “stuff.” The very word objective implies that the thing being observed is independent of the observer.
As I said, an object doesn’t HAVE physical properties. It IS a collection of physical properties. And electron, for example, has rest mass, charge, position, spin, and so on. These properties can be plugged into equations that express mathematical relationships between mass, energy, space, and time. In Newtonian mechanics, there are only 3 basic observables, mass, position in space, and position in time. The concepts of force, momentum, kinetic energy, and so on, are built on these. Here’s the equation for kinetic energy, for example:
Kinetic energy = mass x distance2/time2
A commonly used unit of energy is the Joule. As implied by the above equation, a Joule can be expressed in units of mass, distance, and time. A Joule is actually 1 kilogram-meter2/sec2. In other words, kinetic energy is actually DEFINED by mass, distance, and time.
We tend to think of mass, velocity, and energy as properties “of” an object. But they are not more intrinsic to the object than space and time are. The kinetic energy “of” an object is a function of space and time. But space and time are themselves not constants. They are not “background.” They are changeable. The presence of matter alters the shape of spacetime. Something we think of as intrinsic to an object alters the very environment in which we are trying to measure its properties.
In a way, this shouldn’t surprise us. We are accustomed to seeing objects affecting each other without touching each other. A magnet pulls on a piece of metal. The earth pulls on the moon. Invisible forces are at work. Physicists explain this by suggesting that the objects are exchanging particles with each other, the so-called force particles. But an equivalent way of saying this is that there are 4 basic fields – gravitational, electromagnetic, weak nuclear, and strong nuclear. Some physicists refer to particles, all particles, as local excitations of fields.
So-called “empty space” is not empty at all. It contains what physicists call vacuum energy. It is possible that this vacuum energy is in fact enormous – this is still a major unresolved problem in physics. But in order to explain physical phenomena, physicists have long promoted the idea that “empty space” is constantly “boiling” with virtual particles – particles that are so short-lived that we never actually see them. The presence of these particles may cause space/time itself to be constantly changing shape at very small scales.
Physics tells us that mathematical equations describe physical phenomena. Notice that I said EQUATIONS. An equation is a relationship. Distance, time, mass, energy. The four forces – gravity, electromagnetism, weak nuclear, strong nuclear. All of these are related to each other. An object is a collection of mathematical properties. An observation is an entanglement between the observer and the observed. This inevitably changes the properties of both. The physical is relational.