Gravity - From Newton to Einstein - The Elegant Universe

From the NOVA PBS series "THE ELEGANT UNIVERSE', host Brian Greene guides us through Newton's discovery of gravity to the explanation of it, through Einsteins Theory of Relativity.

Brian Greene is a theoretical physicist and one of the best-known string theorists. Since 1996 he has been a professor at Columbia University.

The Elegant Universe was adapted for a three hour program in three parts for television broadcast in late 2003 on the PBS series NOVA.

http://www.pbs.org/wgbh/nova/elegant/

Category:

Science & Technology

Tags:

• Albert
• Einstein
• Isaac
• Newton
• Theory
• Gravity
• Elegant
• Universe
• Sagan
• Astronomy
• Education
• Big
• Bang
• Cosmos

[hovsec]

i love einsteins story and i remember the first time i heard about relaitvity and started investigating about it blew me away and thought what a genius einstein was to come up with it

[1959info]

In Newton's equation, acceleration due to gravity is used to define gravity or 'weight' of a mass on earth. By releasing his equation from the constant of 'g' (acceleration due to gravity) to the hypothetical variable of 'a' (acceleration of mass) he uncovered the value of force defined in Newtons (the net force required to accelerate a 1kg mass at a rate of 1 meter per second squared. A similar approach to Einstein's constant 'c' (speed of visible light) would unravel many hidden mysteries

[randomacountboy]

if we are on a trampoline, earth's gravity is holding us down. just like a trampoline, there is space. but what is holding planets down in that dip? and not just let it roll out? check my video responce if your confused by my question plz :)

[strangerlover11]

In whatever business thou mayest be, and whatever portion thou mayest be reciting from the Qur'an,- and whatever deed ye (mankind) may be doing,- We are witnesses thereof when ye are deeply engrossed therein. Nor is hidden from thy Lord (so much as) the weight of an atom on the earth or in heaven. And not the least and not the greatest of these things but are recorded in a clear record.Qur'an:10-61.By the Sky with (its) numerous Paths,Qur'an 51:07

[SeanACampbell]

@Eggfriedmice At last count, there were around 70,000,000,000,000,000,000,000 stars in our observable universe.

When you are talking about that kind of scale, then rare things happen all the time. And even the rarest events are bound to happen somewhere in our universe.

[SeanACampbell]

@Eggfriedmice Now if you consider how many objects are actually successful in remaining in orbit around their stars, you will understand that it is "rare". The solar system is enormous, yet only around 8 large objects (and of course various small objects, dust, minor planets etc) manage to stay in orbit.

And it is not as if there are planets around every star. There are about 350,000,000,000 galaxies in the observable universe, each with hundreds of billions of stars.

[SeanACampbell]

@Eggfriedmice It is simply that because the human life span is so short (80 years) and the period that humans have been inhabiting the earth is so short (around about 100,000 years in their "current" recognizable form), and the fact that we have only been observing the universe for a fraction of that time (at least in a form where we would be able to detect a degrading orbit) we do not notice the slight degradation of orbits.

[SeanACampbell]

@Eggfriedmice You also need to understand that planets and their moons are not in a "perfect" orbit - the orbits are degrading in most cases. For example, in the case of the moon, it is moving away from the earth a few centimeters a year.

But a few centimeters on the scale of our solar system is relatively insignificant in the timescales we are talking about. Over the course of millions of years it may be significant, but over the course of the average human life span it would be unnoticeable. 

[SeanACampbell]

@Eggfriedmice It all has to do with the movement of the objects. Any object traveling fast enough in the direction which is at a 90 degree angle to the direction of acceleration (ie. the direction towards the centre of the object it orbits) will remain in orbit. If its velocity is higher, then it will move away from that object. If the velocity is lower, it will move toward that object (get pulled in). 

[Eggfriedmice]

@SeanACampbell I've heard that before and if that's the case, I still find it overwhelmingly convenient that all the planets around all the stars and all the satellites around all those planets are only there because they managed to catch the right trajectory so as they would fall into perpetual orbit. Also, our suns gravity is strong enough so that pluto manages to orbit it (all that way out), yet mercury still isn't close enough to be sucked in unquestioningly? How close would you need to get.

[jesseortiz666x]

Newton didn't DISCOVER gravity, he found out that everything is connected by gravity and came up with the equation that explains it.

[SeanACampbell]

@SuperMagnetizer You are joking right?