While coursing through a series of old tabs that I had saved on my internet browser history, I came across an interesting science website that my physics professor recommended taking a look at four years ago. This website, called the The Scale of the Universe, allows you to zoom in to the smallest bits of matter that theoretical physicists believe to be possible (a Planck length), and zoom out all the way to view the entire visible universe as observed from Earth. Truly a magical sight, but even more magical (and confusing) when we delve a little bit deeper.
When we move toward the very very small and the astronomically large, we are left with theoretical explanations of the universe that seem to contradict what we ‘know’ about space and time. However, we humans are not perfect, and we tend to get confused when talking about really small and really large numbers. Here are some examples, followed by why I believe we are skeptical when reading about these things.
The Very Small
A Planck length, is found to be the smallest possible unit of length, with a value of 10^(-35)m, or 0.00000000000000000000000000000000001m. The idea of a smallest unit of length is puzzling (can’t we cut a Planck length in half?), and the reasoning behind this value comes of quantum physics and includes the theory governing the Heisenberg uncertainty principle, that maximum speed of light (2.998×10^8 meters per second), and the laws of gravitation.
We can only be certain of a measurement to a certain degree. In particle physics, this roughly translates to particles existing in space within a probability distribution, whereby it’s location is more likely to be in one area rather than another. It is consistent with experimental observations to think of a particle as existing as a ‘smear’ across a few measurements (or it’s position existing within a range of locations). At some point, the smearing makes it impossible to determine the actual location or size or velocity of an object in space.
So let’s say we have a test particle shooting toward a stationary measuring particle of unknown location (this is theoretical). We want to know the location of the measuring particle. When they get close to each other, the particles interact, and so by assessing the change in the test particle (velocity, position) we can deduce its location. The laws of gravitation state that any object with mass will interact with other objects of mass, and so this interaction slightly accelerates the measuring particle, and thus it’s position changes slightly. Therefore, we can never know the exact location of the measuring particle due to the distortion that occurs by the two particles interacting. The smallest possible distortion that would occur would involve the briefest interaction possible, which would occur if the particle was traveling at the speed of light, c. When you calculate this distance distortion, you get the smallest meaningful unit of length, the Planck length. Beyond this, even the theoretically briefest exposure to the slightest possible mass will not lead to a movement smaller than a Planck length. Also, any measuring device would necessarily involve larger disturbances resulting in distortions greater than this unit, so matter really does not make any sense when moving smaller than a Planck length.
Imagining such phenomena is complex and confusing! Our concept of the smallest portions of the universe govern physical laws that seem to challenge our experiences with reality- an electron can be a particle or a wave, objects can move through each other. A really interesting example is that when you theoretically cut a Planck length in half, you get a larger length – this concept makes no sense in our larger worlds, but is verifiable and testable fact in particle physics.
We observe that rocks are solid objects, and anyone who has ever been hit by a flying rock, or who has fallen onto a rock can attest to this. However, it is an absolute fact that rocks are made of matter, which is composed of atoms, and atoms are mostly empty space. If we were to examine the inside of an atom, the nucleus would be a single pea in the center of a massive football stadium, with electrons of negligible size (even on this scale) are orbiting around the edges of the nosebleed sections. So rocks, even though they seem solid, are more than 99.9999999% empty space. If we were very very small, we might be able to understand intuitively that rocks are mostly empty, but as humans we live in a different reality with a very different experience of rocks.
It is the experiences we have in our own physical worlds that govern our perceptions of objects like rocks as being solid, but reality contradicts this experience. If atoms were solid (not empty space), the entire universe could fit into a single grain of salt. With this knowledge, the theory of the Big Bang where the matter of the universe is initially contained within a space the size of the tip of a ballpoint pen is a little more appealing conceptually. Without this knowledge, a universe contained in such a small space sounds rightly absurd.
The Very Large
Similarly, we cannot comprehend incredibly large numbers. If we took an average globe at about one foot in diameter, the international space station would be approximately half of an inch above the surface of the model. The moon would be 30 feet away, and mars would be a mile away. The observable universe is about 14,000,000,000 light-years in diameter, because the universe is this many years old and light has been traveling outward at a speed of 2.998×10^8 m/s (299,800 kilometers per second) ever since its beginning. When we look at distant stars, we are usually looking at the ghosts of stars that have long disappeared, but who’s light is still being received by our telescopic instruments on Earth, perhaps for millions of years.
Our ability to understand our universe is severely limited by the brains and sensory organs that we are given with. We can observe an incredibly unimpressive range of electromagnetic radiation (a.k.a light), limited within the visible spectrum (between 400 and 700 nanometers in wavelength). We cannot see radio waves, microwaves (with waves in the centimeter range, not micrometers – a misnomer), infrared, ultraviolet, X-ray, and gamma rays. We can only see the smallest fraction of the universe with our human eyes.
Why do we get into trouble?
These findings raise skepticism in many people, some of which gain distrust in science or its findings. I think that we, as humans, have evolved to explore and make conclusions about the world in a way that is relevant to our survival. A part of this is assuming that we are intuitively objective, and that our perception is the correct one. We have not evolved to understand the incredibly small portions of our universe, because we naturally would not interact with it using our senses; we need testable theories, experimental observation, and special instruments to examine this. Similarly, understanding the massively large universe is not relevant to our experience of the medium-sized world in which we interact.
When we consider this, the notion of intuitive impossibility becomes almost irrelevant. We should not ignore our perception of impossible, but rather be skeptical of it. Our inability to comprehend some of these abstract concepts – the meaning of infinity, for example – come from our perceptions of physical space, and our experiences with the laws governing them. Science is constantly changing its views, modifying them through experimentation and demonstrating facts, and thus science is the process by which we get closer and closer to understanding the reality of our universe, beyond our fallible and biased human experience.
“The joy of life comes from our encounters with new experiences, and hence there is no greater joy than to have an endlessly changing horizon, for each day to have a new and different sun.”
And what a marvelous universe there is, hidden just beyond the horizon of our knowledge, with science taking us closer and closer to what lies at its edge.