Date: October 31, 2010
Title: Space: What Is It?
Podcaster: Alvin Ashworth
Description: “Space” is used often in many disciplines from Astronomy to Philosophy, but what are we referring to when we talk about space? Is it nothing at all? A concept? A physical presence?
In this podcast we’ll take a look at different ideas of what space consists of. We’ll look at the meaning of space that is specific to Astronomy, and how Astronomers categorize different regions of space. Finally, we’ll try to relate the Astronomical definition with some of the philosophical concepts of space.
Bio: Al Ashworth manages an engineering team for a Rhode Island based technology company. He is educated in Philosophy, which led to an interest in Astronomy and Cosmology. He is an enthusiastic follower of NASA projects and a third time contributor to the 365 Days of Astronomy.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Jeanne Jacobs for my son Matthew… Happy Birthday. As you reach for the stars, know that you have love and support at home. We are very proud of you. Love mom and Dad.
Space: What Is It?
The word “Space” is used often in many disciplines from Astronomy to Philosophy, but what are we referring to when we talk about space? Is it nothing at all? A concept? A physical presence?
In this podcast we’ll take a look at different ideas of what space is. We’ll look at the meaning of space that is specific to Astronomy, and how Astronomers categorize different regions of space. Finally, we’ll try to relate the Astronomical definition with some of the philosophical concepts of space.
According to Wikipedia (article on space.):
“The term outer space was first recorded by the English poet Lady Emmeline Stuart-Wortley in her poem “The Maiden of Moscow” in 1842, and later popularized in the writings of HG Wells in 1901. The shorter term space is actually older, first used to mean the region beyond Earth’s sky in John Milton’s Paradise Lost in 1667.”
Let’s look at some definitions of space.
The common sense view is summed up in the “whatisspace” web site: “Space is the limitless, boundless, three-dimensional extent where objects and events occur and have relative position and direction.
In this definition, space is an “extent” meaning, I think, a place where objects can be extended. OK, but what is that place?
The Philosopher Plato believed that only Ideas are real. The physical world is like a shadow of the real world of ideas and spirit. To Plato, space is the empty receptacle that the shadow world exists in. It is no more real than the physical world.
Plato’s student Aristotle was more empirically minded. He defined space as the limit of the surrounding body towards what is surrounded. This is a functional definition.
According to the Catholic Encyclopedia, space exists in the mind only. It is extension without substance, which cannot happen in the real world.
“Nothing” cannot have extension, or dimensions. Although extension without substance is a contradiction, in our minds we are able to separate the idea of substances from the idea of extension, and that’s where the concept of space comes from.
Isaac Newton believed that space is absolute. That is, it’s distinct from the entities that occupy it and from the methods that we use to measure it. Measured space is called relative space. He proved the independent reality of space by using the thought experiment of water in a spinning bucket:
First, hang a bucket of water from a rope. Twist the rope, and then release it to set the bucket spinning. … the surface of the water will at first be flat, as before the bucket began to move; but after that, the bucket by gradually communicating its motion to the water, will make it begin to revolve, and recede little by little from the centre, and ascend up the sides of the bucket, forming itself into a concave figure…. and the swifter the motion becomes, the higher will the water rise, till at last, performing its revolutions in the same time with the vessel, it becomes relatively at rest in it.
Soon the spin of the bucket slows as the rope begins to twist in the opposite direction. The water is now spinning faster than the bucket and its surface remains concave.
The fact that the water is concave after the bucket stops spinning shows that the water is concave not just relative to the bucket, but relative to space itself, which therefore must be a real entity.
Immanuel Kant, born 81 years after Newton, believed that space is a category of human understanding. It’s ingrained in the human mind, part of the way that our minds are constructed. Our minds apply the categories of space and time to what we perceive in order to make our experience understandable.
Albert Einstein combined the concepts of space and time into “spacetime”. Something’s position was a matter of four dimensions: three spatial dimension plus time. Any objects position in Spacetime is relative to the position in spacetime of the observer of that object. Also, the structure of space-time can be altered or “warped” by large objects. I think that this means that space is considered independently real, but I know that may be debatable. This is very esoteric ground and to analyze further you need to be able to do the math.
OK, so why are these philosophical definitions important? As we’ll see, scientific definitions of space concern counts of particles and other substances, but we’re we want to know what it is that these particles reside in.
Astronomers are concerned with Outer Space, which is….
“…the void that exists beyond any celestial body including the Earth. It is not completely empty (i.e. a perfect vacuum), but contains a low density of particles, predominantly hydrogen plasma, as well as electromagnetic radiation, magnetic fields, and neutrinos. Theoretically, it also contains dark matter and dark energy.”
The Ancient Greeks believed that the sky consisted of a substance called Ether, which the God’s breathed. The idea of Ether carried into the 19th century, and it was considered to be the medium through which light traveled. Many problems with Ether developed, including the measured failure of Ether to affect the speed of light waves.
The theory of relativity ended the idea of Ether by making it unnecessary. All phenomena relating to light and electromagnetism traveling through space could be explained in General Relativity without reference to ether.
Earth’s atmosphere consists of several regions including the troposphere, the stratosphere, the mesosphere, and the thermosphere, which extends to 600 kilometers (372 miles) above the earth’s surface.
Nitrogen and Oxygen make up 99% of earth’s atmosphere.
Above the atmosphere, the exosphere starts at the top to the thermosphere and continues until it merges with interplanetary gases in the region that we would call “Outer Space.” In the exosphere Hydrogen and Helium are the prime components and are present at very low densities.
Outer space is the area that is beyond earth’s atmosphere and beyond any other planet or atmosphere.
“Space” is distinct from “Outer Space” and there are two views of where it begins.
The International Aerospace Federation considers the Kármán line to be the dividing line between earth’s atmosphere and space. The Kármán line, named after Theodore von Kármánis a Hungarian-American Physicist, is located at an altitude of 100 kilometers (62 mi). At the Karman line air is so thin that an aircraft must travel at greater than orbital speed to keep flying.
The American National Aeronautic and Space Administration uses a different demarcation. Anyone that has traveled above an altitude of 80 km (50 miles) is considered an astronaut by NASA.
The difference between Earth’s atmosphere and outer space is not fixed. Moving from the earth there is a gradual decrease in the density of hydrogen plasma particles, electromagnetic radiation, magnetic fields, and neutrinos; getting closer to being an empty vacuum, but never becomes completely empty.
Space is divided into several regions above Earth’s atmosphere.
The lowest region of space is Geospace: The upper atmosphere, ionosphere and magnetosphere. The Van Allen radiation belts also lie within the Geospace.
Next, cis-lunar space lies between earth and the moon.
Interplanetary space is the space around the planets and sun in our solar system. This is the location of the Solar wind.
Interstellar space. Space within the galaxy, outside of Interplanetary space. It is occupied by gas and dust.
Finally, Intergalactic space is the Void between galaxies. Intergalactic space is close to being a complete vacuum with an average density of one hydrogen atom per cubic meter.
OK, so we’ve looked at the composition of the regions of space and the definitions of those regions. Have we discovered exactly what is it that particles float in? I think that we’re led back to square one- the Philosophical definitions of space. Space has to be something or it would take no time to travel through it and nothing could be contained in it. So what is space?
I think that the view of Immanuel Kant and the description in the Catholic Encyclopedia makes the most sense. Space is a framework that we apply to organize experience. Space seems like a separate entity to us because we are able to logically isolate space from substance in our minds.
Well, there’s my opinion. I’m sure that there are other ideas out there. If you have one I hope you’ll post it on the 365 days web site. Some questions may not be resolvable by science and I think that this may be one.
I hope that you have enjoyed this speculation, and thank you for listening.
End of podcast:
365 Days of Astronomy
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