Ever since Einstein invented spacetime, it is the preferred medium to explain gravity effects. So, when a star’s light is “bent” from its presumed straight line path, it is because some mass has distorted spacetime through which the light is passing. Although we could just say that gravity affects light, we go further to state how gravity affects light through a distortion of spacetime scenario.
So, in order to fully expose my ignorance, I still have some questions about this spacetime interpretation.
For one, I still have questions regarding the usual examples given. The most common example is to use the distorting of spacetime to explain orbiting planetary bodies (see illustration–courtesy of NASA).
So, somehow the Earth distorts spacetime (I don’t know how) and the satellite is just following the formerly straight lines of space as they curve around the Earth (imagine the Moon tracking along one of those circular lines). Back when I was a nipper, we were taught that an orbiting object is undergoing constant acceleration because its path is constantly changing which requires a force and that force is gravity (F = ma). If the orbiting body is simply following “straight” paths through spacetime, then there is no force acting upon it to cause its path changes, so” no “a” and no “F.” Gravity is “caused” by the distortion of spacetime by embedded masses.
But what about things not in orbit? Let’s say a meteor is plunging into the solar system, presumable following a path created by the distortion of spacetime by the Sun, but the Earth gets in the way. As it approaches the Earth it is accelerating because of the attraction to the Sun and the Earth and it punches a hole right through our atmosphere and, if massive enough, possibly through the Earth’s crust. If the meteor is following a “straight” line established by the Sun, it must be cutting across the “straight” lines established by the Earth, you know the ones all of the satellites are following, no? But, why does it go faster and faster if gravity is just a distortion of spacetime? What is the source of the force causing objects approaching the Sun, like this meteor and all comets, etc. to accelerate all of the way there and decelerate on outward paths?
And just what is spacetime? Is it matter? Is it a field? Is it an energy? How does a mass interact with it? Do they exchange fundamental particles as in all of the hypothetical interactions of particles in high energy physics? How?
How does spacetime expand? And why does it expand? When matter expands it become less dense. When fields expand, they become weaker. But spacetime expands and it just becomes more spacetime, no? How does this happen?
Inquiring minds want to know.
I fully expect that there are explanations I have missed but I think many of these questions are still “open” as we say in the science biz. Unfortunately science writers use language as if all of these are settled and factual, like I read every time the Big Bang Theory is mentioned. According to the standard BB theory the universe is 13.7 billion years old, based upon the “observed” expansion of space. (There is no observed expansion of space. There are phenomena explained using an expansion of space scenario, but that is far from convincing.) This is stated as a fact more often than not, e.g. “the universe is 13.7 billion years old.” This should be stated as “According to the current BBT, the universe is 13.7 billion years old.” Which obviates the embarrassment when occurs when numbers get changed. According to a recent paper, that age needs to be extended out to almost double the current value.
Uncommon Sense 