St. Augustine famously said that God exists outside of time: time is a creation of God, along with the universe; thus there was no “before” the moment of creation; we cannot ask what God was doing prior to that moment, as the realm outside of time is beyond our comprehension.
Modern physics tells us something similar. The Big Bang theory, developed by the Belgian physicist Fr. Georges Lemaître who built upon the ideas of Albert Einstein, says the universe emerged from a hot, dense state — so dense that space and time were distorted beyond what the laws of physics allow us to investigate. Time began with the Big Bang. Lemaître described the universe as beginning on a “day without yesterday”.
How does that work? How can space and time be distorted? I have discussed this some in my series of posts on Black Holes, but now I want to dive into the subject a little more, in a new series of posts on the subject. Click here for all three posts in this new series.
PART 1
You have used electromagnetic (EM) waves today. So have astronomers. Your phone uses a type of EM waves. Radio telescopes and your personal radio use a different type of EM waves. Light is yet another form of EM wave. There are more forms still. All of these “forms” differ from one another only in terms of their frequency. Just as various frequencies of sound have different names (bass, treble, etc.) but are still sound, so the various frequencies of EM wave have different names but are still EM waves.
| EM Waves | Sound Waves | |
| Low Frequency | Radio | BASS |
| Microwaves | ||
| Infrared | ||
| Middle Frequency | Visible Light | MID-RANGE |
| Ultraviolet | ||
| High Frequency | x-rays | TREBLE |
| Very High Frequency | γ-rays | ULTRASOUND |
Therefore there is no more difference between an x-ray and a radio wave than there is between a high-pitched whistle from a piccolo and a low-pitched rumble from a pipe organ.
Our understanding of EM waves is owed in large part to a number of very faithful scientists (see last week’s post). Allesandro Volta developed what we today call an electric battery, setting off rapid development in knowledge and technology regarding electricity throughout the nineteenth century. Michael Faraday investigated the relationship between electricity and magnetism. James Clerk Maxwell developed electromagnetic theory, including EM waves.
In the table above I compare EM waves and sound. Sound waves travel through a medium — usually air when we are hearing them. During the time when the physics of EM waves was being developed, it was presumed that since these were waves, they must also travel through a medium. This hypothesized medium was called the “aether”. Since EM waves travel through space (the light from the stars is an EM wave and it travels through space to reach Earth), the aether would have to exist all throughout the universe yet allow matter to pass through it easily. The thing is, no experiment has ever been successful at detecting any aether.
Einstein came up with an interesting solution to the aether question. He said that there was no aether — that EM waves (such as light) simply travel at a fixed speed (300,000,000 meters/sec or 186,000 miles/sec) as seen by all observers. This speed is therefore a universal constant. Thus it is often written as c = 300,000,000 m/s = 3 × 108 m/s (in scientific notion) = 186,000 mi/s.
This was a very different sort of idea. Let’s see what this means for light waves compared to the behavior of sound waves.
Imagine that there is a vehicle moving at a speed of 200 m/s through air (red dot in the figures below). The air is the medium for sound waves. There is also an observer (purple dot) who is at rest with respect to the air (below, #1).
When the vehicle gets to the location opposite the observer, it emits a sound pulse (#2). The observer sees the sound waves travel outward from the point of emission, moving at the speed of sound in air (340 m/s) as shown in #3O. However, from the point of view of the vehicle, the vehicle is at rest. The air is rushing by at 200 m/s. The sound wave in front of the vehicle is moving away at 340 – 200 = 140 m/s, while the sound wave behind it is moving away at 340 + 200 = 540 m/s, as seen in #3V.
This view of being at rest with the air rushing past and the sound wave moving away is perfectly valid. To use another example, imagine a truck moving down a road at 90 mph. A person in the back of the truck throws a ball forward at a speed of 50 mph. To the driver of the truck, the ball is moving at 50 mph. But to an observer standing on the road, waiting to catch the ball, the ball moves at 140 mph. Both 50 mph and 140 mph are “correct” speeds for the ball, depending on whose point of view you are talking about. It is not the case that one is right and the other is wrong.
The driver and observer differ on their measurements of the speed of the ball, but they do not differ in their understanding of the laws of physics. For instance, they will both use the same equations for gravity and air friction in determining the ball’s motion. This idea that, whereas the exact details of a problem are dependent on (or relative to) the observer in question, the laws of physics are the same for both is a concept that has been understood since Galileo and Newton, and is called Galilean or Newtonian Relativity.
This applies only in the case of observers moving at constant velocity. Such observers are obeying Newton’s 1st Law of motion, otherwise known as the Law of Inertia. It is the law that says an object in motion remains in motion, etc. Thus we say this form of Relativity applies for inertial frames of reference. If the observers are accelerating then they are not in an inertial frame of reference and things get a lot more complex. For example, if the truck is accelerating, a ball sitting in the truck will start rolling around on its own.
Einstein modifies this only slightly for what is called his Special Theory of Relativity. Einstein agrees that the laws of physics are the same for all observers in inertial frames of reference. But then he adds that all observers will agree not just on the laws of physics but they will also agree that light moves at the same constant velocity (namely c = 3 × 108 m/s) regardless of how they may be moving. The speed of light is a constant for all observers. There is no aether, no medium with respect to which the speed of light is measured.
So how does this change things? Let’s repeat our example above, but using light (an EM wave) instead of sound. Imagine that there is a vehicle moving at a speed of 200,000,000 m/s or 2 x 108 m/s relative to an observer. There is no aether for EM waves so there is no medium for the observer to be at rest with respect to.
When the vehicle gets to the location opposite the observer, it emits a light pulse. The light waves travel outward from that the point of emission at a speed of 3.0 x 108 m/s (#3O). However, from the point of view of the vehicle, the vehicle is at rest. Period. The purple observer moves by at 2 x 108 m/s but so what? What does that have to do with the light pulse the vehicle emitted? There’s no medium rushing by. The light pulse moves off in all directions at 3 x 108 m/s (#3V). The light in front of the vehicle is moving away at that speed, and the light in back of the vehicle is moving away at that speed. This is very different from the sound example.
Similarly, imagine a truck moving down a road at 90% of the speed of light (c). A person in the back of the truck shines a light forward — the light moves at speed c. To the driver of the truck, the light moves at c. But to an observer standing on the road, the light also moves at speed c. If the light was like the ball in the previous example, we might expect the observer on the road to see the light moving at 190% of c, but no. All observers see light as traveling at c = 3.0 x 108 m/s no matter what.
Once you accept this, everything gets strange, including time. We’ll get into that in Part 2 of this series.
