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In the end, a force arises when a particle tries to follow a spacetime geodesic that deviates from a straight line, mostly due to the presence of “time curvature”, that is, due to the fact that clocks tick at different rates at different points in a gravitational field.
They did, to an extent.
But first let's step back a little bit and talk about IQ heritability.
IQ is highly heritable, and that heritability is largely driven by genes (from 50% to more than 70% ... (more)
In the end, a force arises when a particle tries to follow a spacetime geodesic that deviates from a straight line, mostly due to the presence of “time curvature”, that is, due to the fact that clocks tick at different rates at different points in a gravitational field.
From Your Digest
Viktor T. Toth, IT pro, part-time physicist
Answered Jul 25 · Upvoted by Frederic Rachford, Ph.D. physics - Condensed Matter / Electrodynamics and Mike Nightingale, MPhys Physics & Astrophysics, University of Exeter (2019)
First
of all, before you read any further: Go and grab something heavy. Say, a
brick. Feel it in your hands. Feel as it is trying to pull your hands
down.
If you do not feel a force, you need not
read any further. Please leave the room. I’ll wait a few seconds while
you grab your things.
[…]
OK, now that we have established that gravity is a force, let’s take a look at how it works.
Newton’s
law of gravitation is an example of action-at-a-distance: two bodies
influencing each other over a distance without anything mediating that
influence. This troubled Newton so deeply, he delayed publishing his
work on gravity for many years; and even after it was published, he had
deep misgivings, as evidenced, e.g., by these words from a letter to
Bentley in 1692 or so: "It is inconceivable that inanimate Matter
should, without the Mediation of something else, which is not material,
operate upon, and affect other matter without mutual Contact [...]
Gravity must be caused by an Agent acting constantly according to
certain laws".
In the late 1800s, thanks to the work of Maxwell, the concept of a field
was born in physics. Electricity and magnetism (and incidentally,
light) were explained by the concept of the electromagnetic field and
its fluctuations. Soon it became evident that gravitation must also be
mediated by a field. But what form shall that field take?
Gravity has an important property: Unlike other interactions, gravity is universal.
All material particles respond to gravitation the same way, regardless
of their material composition or other properties. This is what made
Einstein realize that gravity is necessarily a geometric theory: that is
to say, the effects of gravity are indistinguishable from the effects
of acceleration, so if the latter can be described using geometry, so
can the former.
But let me now jump ahead a bit
and ask… could we not describe other forces, e.g., electromagnetism,
using geometry? And the answer is that we can… but with an unpleasant
twist. The geometry “experienced” by particles with different
charge-to-mass ratios will differ. There will also be a “reference”
geometry, the one sensed by neutral particles that do not respond in any
way to the electromagnetic field.
In contrast,
because gravity is universal, all particles experience the same
geometry. Not only that, but there are no gravitationally neutral
particles, so there is no reference geometry that we can explore or
measure. Really, the only geometry in town is that determined by
gravity.
So whereas for electromagnetism, the
geometric interpretation is either a curiosity or a useful mathematical
tool depending on your preference, for gravity, it has unique
significance. This is what allows us to proclaim that gravity and
spacetime curvature are really the same thing, because no matter what
you use to measure spacetime: rulers, beams of light, etc., you will
experience the same distorted geometry when gravity is present.
In
the end, a force arises when a particle tries to follow a spacetime
geodesic that deviates from a straight line, mostly due to the presence
of “time curvature”, that is, due to the fact that clocks tick at
different rates at different points in a gravitational field. This force
may be a fictitious force like the infamous centrifugal force, or it
may be a real force, like the centripetal force, when there is something
(say, a floor) in a body’s way preventing the body from following a
geodesic. Either way, it is a very real force that you can feel, measure
with a force gauge, or even experience as pain if you are clumsy enough
to drop the aforementioned brick on your feet.
TL;DR:
Gravity is a force. It is mediated by a field that has a geometric
interpretation. This geometry applies uniformly to all particles as the
only geometry that can be measured or experienced, because gravity is
universal.
David Kahana, physicist unhinged
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Answer ·
Jack Fraser, Master's Physics, University of Oxford (2018)
Answered Mar 11 · Upvoted by Jyothishraj Nambisan, BS-MS Physics, Indian Institute of Science Education and Research, Thiruvananthapuram (2017) and George Hagstrom, I have a Phd in physics from the University of Texas at Austin, the topic of my thesis was plasma p…
As far as we know today, there are 4 fundamental forces of nature:
- Electromagnetism
- Gravitation
- Weak Nuclear Force
- Strong Nuclear Force
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Adrien Lucas Ecoffet, Quora engineer. Frenchman. Americanophile.
But first let's step back a little bit and talk about IQ heritability.
IQ is highly heritable, and that heritability is largely driven by genes (from 50% to more than 70% ... (more)
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Håkon Hapnes Strand, 2177 FIDE. Personal friend of Magnus Carlsen.
They do so because having a better position is more valuable than having more time on the clock.
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Elizabeth Muller, Unconventional environmentalist, entrepreneur, dancer, mom
I studied negotiation in my master’s program, and got some hands-on practice with it at the OECD and in my subsequent jobs.
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Senia Sheydvasser, PhD student in Mathematics
Answered Dec 10, 2016 · Upvoted by Jesse Raffield, Master's degree in physics and Ed Caruthers, PhD and post-doc work in Physics at UT Austin. Published papers in electronic properties of metals,…
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Jack Fraser, Master's Physics, University of Oxford (2018)
Here's an explanation using the only language 6 year olds understand:
LEGO.
This is Jabba's Sail Barge, LEGO Star Wars set No. 6210.
747 parts and 8 minifigures. It was my pride and joy back in 2006.
Now.
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