Physicist explains General Relativity | Sean Carroll and Lex Fridman

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GUEST BIO:
Sean Carroll is a theoretical physicist, author, and host of Mindscape podcast.

PODCAST INFO:

SOCIAL:

[LexClips]

Guest bio: Sean Carroll is a theoretical physicist, author, and host of Mindscape podcast.

[joelglass]

He has a great voice. Carrol is one of the most respected science communicators and scientific theorists in his field.

[StephenB_IndependentThought]

Einstein published 3 papers all in 1905 - Light as particles and not just waves, special relativity, and proof that atoms exist.
That's incredible, that's genius.

[the_one_eyed_man_is_cursed]

Sean at his best. Some new and interesting facts about Einstein's gravitas. A stepped-up version of Lex, too. Good clip.

[Raging.Geekazoid]

So special relativity is based on the Michelson-Morley experiment (1887), which found that the speed of light is the same for all observers. This seems ridiculous based on classical intuition, but once you've accepted it as confirmed fact, SR follows from it directly. Einstein's genius was being completely open-minded about following confirmed truths to their logical conclusions.

The motivation for general relativity is even older: It had been known since Newton's time that inertial mass (resistance to acceleration) and gravitational mass (mutual attraction of massive objects) are exactly the same. Again, from a conceptual standpoint, all Einstein had to do (in addition to the math of GR, which is much harder than SR) was clear his mind of traditional assumptions and find the theory implied by that simple, universal fact.

[philmurphy]

I like Lex, he's a very good interviewer

[dgsean]

Fun fact kids. Dynamic Gravity explains all perfectly and its math actually perfectly calculates gravity, dark energy, and dark matter with the same equation. And there are no paradoxs like GR. Its just a better theory of gravity.

[_kopcsi_]

no, it wasn't Einstein, not even Minkowski, who realised that space and time form a unity. it was Lorentz. Lorentz was the one who understood first how abstract algebra is related to spacetime and to relativity. he developed the Lorentz-symmetry group and so the Lorentz-transformation. and he was the one who proposed to treat space and time as one. actually Einstein just used Lorentz' insights and defined the two postulates of relativity. most of the credit should go to Lorentz. just like the electromagnetism was mainly described by Faraday, he was the one who realised that electric field and magnetic field are two aspects of the same thing, he invented the concept of field lines, and he realised all the four principal laws of electromagnetism. but his mathematical background was poor, so Maxwell formalised these laws using vector calculus (which was a new thing back at that time).

and no, this "explanation" does not lead to real understanding, at most to superficial knowledge and so to an illusion of understanding. in order to deeply understand relativity, you must understand its underlying mathematics and its relationship with other physical laws. this is something that you cannot spare. not even when someone explains well the given theory and its certain aspects.

e.g.:
- the relationship of gravity with electromagnetism, their symmetry properties, bosons and graviton, linearity (vector field description, i.e. antisymmetric tensorial description) [spin-1 boson (photon) and symmetric sources (charges)] vs nonlinearity (tensor field description, i.e. symmetric tensorial description) [spin-2 boson (graviton) and symmetry breaking sources (masses)], Maxwell-equations and gravitoelectromagnetism, field theory (quantum) based description vs geometrical (relativistic) based description etc.
- curvature, as frequency and spectrum from Fourier-analysis (x-k duality)
- force, as a human-made construct and concept: in fact, gravitation is not a force, but an interaction, and in the sense of relativity, gravitation manifests itself through the curvature of space-time, i.e. the rotation of the light cone (i.e. the gradual exchange of the roles of space and time). ergo: relativity eliminates the concept of force and its necessity and legitimacy by including and extending Euclidean space (to non-flat, i.e. curved non-Euclidean spaces), the concept of straightness (to geodetic lines) and the concept of inertia (to motion alongside geodetic lines).

not to mention the even deeper aspects of reality which share characteristics with quantum physics (e.g. the introduction of the observer, i.e. the subject, and so the subject-centred nature of the object, i.e. of reality).

[ZeusCristo]

I am so much dumber now after reading these comments 🤦‍♂️

[wulphstein]

Can someone explain to me why: over the last 50 years of studying black holes, we learned that the clock slows down as you approach the event horizon (go deeper into the gravity well). But nobody has proposed that there could be higher gravity potential energy "planes" or "dimensions" where the clock runs faster. Like a skyscraper where the event horizon is in the basement, we are in the first floor. The clock runs faster on the second floor, so that spaceships can move faster on the second gravitational floor or dimension. Maybe you have to get to the 50th gravity floor, where the clock runs 50x as fast, before you can think about using the 50th floor for interstellar travel.

[robertmontague]

Lightspeed is fixed at 300, 000km/sec because light is electromagnetic radiation and it's speed is being throttled by the permeability and permittivity of space itself. Maybe "aether" is just a metaphor for the resistance of space in limiting the speed of light.

[michaellowe]

It is odd to me that it is considered an accomplishment that they got rid of the aether, but then immediately replaced it with space-time and quantum fields. It seems like the aether never went away. They just got better at describing it.

[RazWorld..]

✍🏽With General Relativity we first need to understand Space-Time :

👆🏽Spacetime is a four-dimensional construct that combines the three spatial dimensions (length, width, height) and one time dimension…So according to G.R this spacetime is flexible and can be distorted or curved.. and thats due to Energy & Mass of the object around it. (Planets 🪐🌎 or ☄️🌚 ✨ or etc)

Nb* and this curvature guides the motion of objects ☄️🪐🌎🪨, leading to what we observe as gravitational attraction i.e the force of gravity as we know it -same pulling effect in a broader perspective now✍🏽

[SamanthaPyper-slye]

Theorem 7: The vacuum expectation value of the energy-momentum tensor in general relativity is proportional to the metric tensor.

Proof:
In general relativity, the energy-momentum tensor T_μν is a symmetric second-rank tensor that describes the density and flux of energy and momentum in spacetime.
The vacuum expectation value of T_μν, denoted by ⟨0|T_μν|0⟩, is the expectation value of T_μν in the vacuum state |0⟩.

According to the Einstein field equations, the energy-momentum tensor is related to the curvature of spacetime via:
R_μν - (1/2)Rg_μν + Λg_μν = (8πG/c^4) T_μν
where R_μν is the Ricci tensor, R is the scalar curvature, g_μν is the metric tensor, Λ is the cosmological constant, G is Newton's gravitational constant, and c is the speed of light.

In the vacuum state, the energy-momentum tensor vanishes classically, i.e., T_μν = 0.
However, in quantum field theory, the vacuum state has zero-point fluctuations that give rise to a non-zero vacuum expectation value of T_μν.

By the principle of general covariance, the vacuum expectation value of T_μν must be proportional to the only available second-rank tensor in the vacuum, which is the metric tensor g_μν:
⟨0|T_μν|0⟩ = κg_μν
where κ is a constant.

Substituting this into the Einstein field equations, we obtain:
R_μν - (1/2)Rg_μν + Λg_μν = (8πG/c^4) κg_μν
This implies that the vacuum energy-momentum tensor acts like a cosmological constant term in the Einstein equations, with an effective cosmological constant given by:
Λ_eff = Λ + (8πG/c^4) κ
The fact that the vacuum expectation value of the energy-momentum tensor is proportional to the metric tensor suggests that the concept of zero or nothingness may be deeply connected to the geometry and topology of spacetime, and may play a crucial role in the large-scale structure and evolution of the universe.

[dyvercity]

Comment section is bunch of people trying to sound smart saying stupid shit

[taz]

GRAVITY EXPLAINED, universe is made of minute cells once contained in a universal
shell that was broken or deformed by an external force.
this produced expansion creating a true void that must not exist,
leaving the cells to expand or split, I believe the destruction or
splitting of cells is where all matter originates,
therefore all the contents of this universe will become matter
and the universal matter will disperse or be contained
by an outer external force or medium.
The cells must penetrate already created matter to a degree, becoming harder the denser it is, until it is so dense it is impossible. thus the push back is multiplied infinitely
causing corresponding gravity push...
As far as so-called gravity it is plain to see that there is no attraction, only an external push
forcing matter together .
Imagine an oil filled rubber ball each molecule of oil must have the same force upon it.
Then introduce a foreign particle of the same size and density then each molecule will have slightly
higher pressure upon it nothing will coalesce
then add a larger or denser body with larger or harder surface to be pushed upon by the other molecules
all the molecules will feel a small amount more push but the nearer the large body cells will get pushed harder.
[this energy really comes from the constant push from the ball membrane or what exists outside it]
then introduce a smaller dense body in the vicinity of the harder pushed cells.
if the number of hard pushed cells behind this body is higher than the ones between it and the large body then gravity is achieved, , , unless the pull from the expanding universe shell is greater..
Without resistance to these cells energy would not be forced to navigate a wave pattern,
the cells would not become excited and light as we know it would not exist .
Energy waves passing through harder pushed cell formations will deviate around
the reason they are pushed.
Hard pushed cells may be deformed from a sphere into an ovoid making it harder to rotate,
also making energy travel differently
The universe itself may be such an ovoid thus the reason for expansion.
Magnets must electronically rearrange the cells shape and alignment making the rearranging object harder or easier to navigate between depending the manufactured configuration.
As far as Quantum physics goes we do not have any real data so mathematical
physics is applied and comes up with sometimes fanciful answers to fit a paradox.
Understanding a data lacking subject has always failed people already in this
field would do best just striving for accurate observation as some early astronomers did.
An understanding will develop with detection instruments and supercomputing enhancements,
seeing it first hand. some bright spark will discover the bleeding obvious and mathematise it.
We must determine the size and density of each cell by measuring each light wave
in relation to one another, and the number of cells between each crest
and finding the correlation that would fit all known energy waves if this can be achieved, the next
step must be to create
corresponding energy waves before a moving object creating an air in sand effect thus help said object closer to the preceding wave speed
Initial measurements should be simple two dimensional with known wave patterns overlaid on the same plane and begin with spherical solid cells filling the voids between the crests of all waves.
First, hoping all the energy waves respect the integrity of each cell, if not some types of energy waves
may penetrate part of the cell, as do they penetrate some matter.
black holes are remnant void bubbles still trying to eliminate the space where cells are absent, destroying surrounding cells and creating matter and drawing existing
matter to fill the void .billions may have succeeded leaving small super dense spheres but most can't keep up with the constant universe expansion and will take all
their surrounding galaxy and more.
No matter how beautiful and pleasant maths is, since the mid 60's, it has blinded physicists
before then a physical notion was envisaged then came out the ruler to see if it would stack up.
These are some answers to how things unfolded but surely the harder question is why.
Why has life evolved to a stage that we can pose these questions?
Surely non existence would be the easier option, without struggle without knowing about
your inevitable destruction personally and universally this question is the real puzzle.
This is why the emergence of conscience coincided with a genetic predisposition towards
a god culture everywhere on earth, a genetic valium so to speak.
which must be ameliorated not railed against by atheist dissenters, its just DNA evolved a part of
our bodies to believe so as to survive longer.

The answer can only be chemistry, all life is simply a chemical reaction, the same as the
stars react with each other, no matter how complicated its components become it must rely
on the basic building blocks to exist, my thoughts while writing this are governed by
a chemical reaction and the lightning created by the reaction.
Therefore if matter has no will and the meeting of different types of matter will react
differently then the meaning of life has the same weight as mixing paint, And in theory the universe could become sentient itself, life and death is
eventually inevitable wherever matter coalesces .

[kokomanation]

In special relativity many equations use the Lorentz factor another great contributor to that great theory along with Minkowski

[_kopcsi_]

the fundamental difference between space and time can be observed in the theory of relativity in several ways. e.g. in terms of the signs (see: Minkowski metric), but also in the fact that while in the case of space the straight line (geodesic line, i.e. inertial motion) between two points gives the shortest path, in the case of time the straight line (geodesic line, i.e. inertial motion) between two events gives the longest time, but all this is also analogous to the fact that in both special and special relativity we are talking about spacetime rotations (in special relativity this is given by the Lorentz-symmetry or Lorentz-invariance, while in general relativity this is given by rotation of the light cone due to the gravity described by Einstein's field equations), i.e. a kind of antisymmetric relation between space and time, and this is exactly what is reflected by the kinetic and gravitational time dilations.

[vicioustwist]

First, and foremost, all of the actual hard work that underlies Einstein's work was done by other people: Lorentz Transformation, Maxwell's equations, Michelson-Morley experiment, ect. These works actually created the postulates which Einstein basically borrowed, i.e. the speed of light is the same for all observers at constant speed no matter the velocity of the observer, the transformations necessary to interpret space/time, ect.. Einstein didn't come up with the concept of relativity - a concept dating back to at least Galileo Galilei. Even Einstein's thought experiment of a rocket or elevator in space is just a reinterpretation of Galileo's "moving ship on a calm sea" thought experiment. Secondly, the formulas for magnetism, electricity and gravity are so profoundly similar, it suggesting that gravity is a force consistent electricity and magnetism. Lastly, the concept of "the fabric" of space and the "warping" of space/time (often diagrammed on a space-time diagram, along with the conical representation of light on such a diagram), to describe gravity as not a force, in my opinion, is almost idiotic. Even as physicists who describe gravity as the warping of space, still work with the concepts of gravitons and photons, and describe both gravity and light as acting through waves.

[rwutube]

So when is Lex interviewing Terrence Howard? 😂