Mea Vita: Carpe Diem: gravity

Showing posts with label gravity. Show all posts

Tuesday, July 30, 2024

You Don’t Accelerate When Free Falling

Speed is relative.

Acceleration is absolute.

If two objects in space are moving closer to, or further away from, each other at a constant speed, there’s no way to know which once is moving because speed is relative.

But, if two objects in space are moving closer to, or further away from, each other at a variable speed, we can figure out which one (or both) are changing speed because acceleration is absolute. This is how accelerometers work… they measure the absolute change in acceleration.

Keep in mind that acceleration isn’t just a change in speed, acceleration can also be a change in direction. An object can move at the same speed, but still experience acceleration if it changes direction.

We say that an object dropped from a building accelerates at 9.8 m/s², but that’s actually not the case. If we drop an accelerometer from a building, it will register 0g’s of acceleration on its way down and this is completely accurate. What’s really happening is that, since spacetime is warped, the ground is moving toward the dropped object at an accelerated rate.

To picture this, think of a satellite in orbit, such as the ISS. It, too, seems to be accelerating at 9.8 m/s² as it falls toward earth, but its speed doesn’t change. Instead, it’s literally following an unaccelerated straight line through spacetime. Whether falling from a building or orbiting earth, both are weightless conditions and, therefore, there’s no acceleration.

Another way to think of this is imagine traveling in the passenger seat of a car that’s moving at a constant speed of 25 mph. You can easily throw a tennis ball up and catch it without any problems. This is because there’s no change in forward or lateral speed; hence, no acceleration. Now, continue to do this while the car is making a turn at a constant speed of 25 mph through an intersection. The ball will appear to move to the side window during the turn; and the further the ball is from the side of the car, the faster it will move relative to the window. This will give the ball the appearance that it’s accelerating but it's actually the car that's accelerating around the ball.

The next big question to answer is how and why does matter curve spacetime?

Tuesday, July 16, 2024

Gravity is not a Force

Gravity is not a force because it’s not mediated by a force carrier. Rather, it’s one of the four fundamental interactions in the universe:

1. Electromagnetic force

2. Strong nuclear force

3. Weak nuclear force

4. Gravity

The first three interactions are forces meditated by quantum particles. Specifically, photons, gluons, and, W & Z bosons, respectively. These force carriers mediate each force, but only photons and gluons are energy. In other words only photons and gluons are particles without mass and they move at the speed of light whereas the W & Z bosons have mass, so they will travel slower than the speed of light.

Of the two force carriers that are energy, photons have an infinite range while gluons have a range comparable to the diameter of a proton.

Gravitons

How do we know there isn’t some undiscovered quantized particle of gravity speculatively called the graviton? Well, if there was one it would still only move at the speed of light and no faster. And gravity waves (i.e. the effects of gravity) have been observed to propagate through space at the speed of light. But these gravity waves appear to only be ripples in the fabric of spacetime much like water waves oscillating in the ocean.

If the graviton particle did exist as a force carrier, moving at the speed of light, then how could it escape from inside a black hole across the event horizon? In other words, how would the effects of gravity be observed outside the black hole? How could gravity communicate from beyond the event horizon? For this to happen escape the velocity of any particle reemerging from a black hole, like gravitons, would need to exceed the speed of light through spacetime.

So, while a particle can’t move faster than light through spacetime, spacetime can move faster than light. The law that nothing can move faster than light only applies to particles moving in spacetime – it doesn’t apply to spacetime itself. This doesn’t violate causality since information can’t move faster than light through spacetime.

You can think of gravity as spacetime flowing like a river into mass, called The River Model of General Relativity.