I am reading a book by Carlo Rovelli, Seven Brief Lessons On Physics, and would like to check if I have understood something. Apologies if my question is badly phrased, feel free to edit where appropriate.
I am not a physicist, just an enthusiast.
It was this excerpt that made me think gravitational waves had something to do with time.
The heat of the black holes is like Rosetta Stone of physics, written in a combination of three languages-Quantum, Gravitational and Thermodynamic - still awaiting decipherment in order to reveal the true nature of time
And the following that made we wonder if they were to do with space as well? My understanding is that space and time are synonymous?
The heat of black holes is a quantum effect upon an object, the black hole, which is gravitational in nature...
It was the next line, following that inspired my question was this,
... It is the individual quanta of space, the elementary grains of space, the vibrating 'molecules' that heat the surface of black holes
Talking about the gravitational field being space-time
The gravitational field, as we saw in the first lesson, is space itself, in effect space-time
Text referred to in the 'First Lesson'
Einstein had been fascinated by this electromagnetic field and how it worked... soon came to understand that gravity, like electricity must be conveyed by a field as well... the gravitational field is not diffused through space; the gravitational field is that space itself
Question: Is space-time 'made of' gravitational waves? Is that field it's fundamental building block?
It seems to me from all of this that space-time is indeed
Answer
I'll try to boil down several of your questions and answer what I think is most fundamental, and hopefully clarify things in the process:
Gravity is completely synonymous with the shape of spacetime across all 4 dimensions (3 space, 1 of time). The reason we speak of spacetime is thus: When you (having negligent mass) stand in a "gravity field" such as that caused by a massive object such as the Earth, you notice 2 things:
First, that space seems to have a direction, i.e. objects will "fall" towards the center of the dominant mass
Second, that your watch will tick somewhat more slowly than it did when you were far away from this gravity well.
These phenomena of acceleration (a gradient in space) and changes in the rate of your watch ticking (so a gradient in time) is why we don't speak of space and time as separate entities - they are inextricably linked, and movement through one affects your movement through the other. The stronger the gravity field you're exposed to (so the more massive the object you're near), the slower your watch will tick when compared to someone standing safely outside the field. Spacetime is the fabric of the universe - so far as we know, there's nothing "under" it, nothing that it is "made up of" - and GR treats it as such. So when you think of spacetime, think of it as a landscape of hills and valleys in both 3D space and in time, all caused by the various masses that reside there, and understand that those hills and valleys are gravity.
Now, gravity waves, then, are ripples in this landscape that can be caused by an accelerating massive object. So if two black holes accelerate and smash into each other, some ripples in spacetime will travel out from the disturbance and we may be able to detect it.
With our understanding of what gravity is above, what would a gravity wave be expected to 'look like?'
We'd expect to be able to pick it up one of two ways: Either by a change in space (seen as a distance fluctuation between 2 points in our detector) or a change in time (an aberration in the rate a very reliable clock is ticking). Which now makes perfect sense, because gravity is simply the shape of space and time, bound up together.
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