Gravity: Einstein's More Than 100 Years Theory Still Relevant

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Every day we wake up and stand up from the bed, pick a toothbrush, or drink a cup of coffee, or just stand, we can do all these stuff due to effects of gravity.

What if someone could "switch off gravity? It is analogous to letting go of a string holding a helium-filled balloon; everything not anchored to earth would fly straight into space. In buildings, people would float upwards till they bump into the ceiling. Only things anchored to earth may not float away immediately, but with time even the Earth itself may likely break up into bits and float away into space.

^{Credit (Pixabay): Zero gravity}

Yes! It is also held together by gravity. We do not want that to happen, do we?

What is gravity?

First, gravity is not a force. But if that is true, what is it since it is common knowledge from elementary physics is that it "pulls things".

But shouldn't forces be involved since it could pull things?

But in the real sense, it is better we replace "pull" with "accelerate" which is a more fitting term.

Now that we have it out of the way we may now attempt to describe what gravity is.

Using the Einstein's general relativity concept, gravity is taken not as an interaction but as a deformation of space-time. Since space-time is not flat object, tend not to follow straight trajectories.

The Fabric and Ball Affair

Back to elementary science again, we all know that matter is is anything that has mass and occupies space. Also, mass is not the same as weight as weight is dependent on effects of gravity.

Every single atom has mass, and most of the sub-atomic particle constituent of the atom does have mass too. The bigger the mass of a particle the more it warps the "fabric" of space surrounding it.

For illustration purposes, consider the picture of the bed with a clean sheet of fabric spread neatly and taut around the mattress. That is the "fabric of space". If you spread ball bearings all over the bed, each ball bearing would make a dent in the fabric.

If two ball bearings are close together, there is a possibility of the combined dent in the bedsheet making them touch.

To push this illustration further, if you suddenly picked up a bowling ball ( or shot put ball) and placed it on the bed, it would make a dent far much bigger than the small ball bearings.

That would cause other ball bearings to slope towards the ball (the bowling ball would move slightly towards the ball bearings, but since the movement is slight you may notice the bowling ball move.

This analogy defines gravity as seen in two-dimensional bed. But in three dimensional, it acts in every direction and not just across a plane.

Credit (Wikipedia): A two-dimensional projection of a three-dimensional analogy of space-time curved around Earth.

According to Einstein, the same way that the ball bearings on the stretched bedsheets cause it to sag, so do the planets and stars create the space-time warp.

The Earth gets drawn to the Sun but not into it. That is because it is moving at a certain speed.

The planets never fall into the Sun because of the speed at which they are travelling. According to the theory, energy and matter distort space-time, curving it around them.

This effect explained in Einstein's general theory of relativity which he wrote in 1915 to describe gravity. This argument is valid as of today as none had disproved it.

An epic victory over daunting challenges, or a costly project that should never have flown? After nearly half a century of work and US$750 million spent, Gravity Probe B, one of NASA's longest-running mission programmes, has finally achieved some scientific closure. But it has yet to quiet its critics.

On 4 May, researchers released the results of a tortuous five-year data analysis that relied on the largesse of a Saudi funding agency to complete. The verdict, to be published in Physical Review Letters: Einstein was right. "I am both glad and relieved that we pulled this off," says physicist Francis Everitt of Stanford University in California, who has led the effort since the beginning. Source

What was Einstein right about? He was right that an object such as the Earth does indeed distort the fabric of space and time.

References:

• When Gravity is "Switched" Off
• Troubled Probe Upholds Einstein, Nature | Nature
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