Anybody want to listen to Richard Feynman for 9 hours explaining the laws of nature? Guessed so!

I’ve found very rare Richard Feynman’s lectures on Physics for all physicists and amateurs!

The following are a collection of rare lectures by the man himself (MP3 Sound):
V1 Ch07 Theory Of Gravitation – 51:42 (20.4 MB)
V1 Ch08 Motion – 53:46 (23.3 MB)
V1 Ch09 Newton’s Laws of Dynamics – 54:42 (23.9 MB)
V1 Ch10 Conservation of Momentum – 53:44 (23.4 MB)
V1 Ch11 Vectors – 52:41 (23.2 MB)
V1 Ch12 Characteristics of Force – 59:36 (26.1 MB)
V1 Ch13 Work and Potential Energy 1 – 55:45 (24.4 MB)
V1 Ch14 Work and Potential Energy 2 – 52:15 (22.8 MB)
V1 Ch15 Special Theory of Relativity – 50:00 ( (25.6 MB)
V1 Ch16 Relativistic Energy And Momentum – 54:57 (24.7 MB)

You can download all from RapidShare for free. The lectures are stored in RAR files, and can easily be unpacked using the free tool 7-Zip (for Windows and Linux):

RapidShare – Feynman Lectures 7-9.rar (66.2 MB)
RapidShare – Feynman Lectures 10-12.rar (71.3 MB)
RapidShare – Feynman Lectures 13-15.rar (71.6 MB)
RapidShare – Feynman Lectures 16.rar (24.3 MB)

Each of the first three RAR files has three lectures in them, and the last one has lecture 16 alone.

Enjoy!

“I agree that photons don’t accelerate LOCALLY. But at cosmological distances, their travel speed relative to both the observer and emitter MUST change. Otherwise, how could distant galaxies have been receding at superluminal velocities at the time of emission, yet the photons approach us at exactly c today?”

You grasp the math better than me, but I think you have got trapped in the same “logical confusion” as me. It’s probably “over bold” for an amateur like to tell you how to think, but after debating this topic over the last weeks, the logic finally make sense:

* We cannot visually see anything that has moved toward us at superluminal speed, including redshift or photons.

* We can calculate, using comoving distance and cosmological time, that the objects that emitted light towards us 700 million years after the big bang, *NOW* should be accelerating at superluminal speeds, at physical distances further than 13,7 light years. BUT please observe – we cannot physically see these objects *NOW*.

Take a good look at this picture of the embedded Lambda-CDM geometry

The brown line on the diagram is the worldline of the Earth (or, at earlier times, of the matter which condensed to form the Earth). The yellow line is the worldline of the most distant known quasar. The red line is the path of a light beam emitted by the quasar about 13 billion years ago and reaching the Earth in the present day. The orange line shows the present-day distance between the quasar and the Earth, about 28 billion light years.

Here is very basic and helping information from good old Wikipedia – Understanding the expansion of space

Speedy

> “Sigh – this is a coordinate dependent quantity and so there is no single “correct” answer.”

So much sighing and groaning… I feel like the foolish Kung Fu Grasshopper at the knee of the great master.

I have agreed that there are an infinite number of coordinate systems which yield an infinite number of different perspectives. BUT, I think there is at least one coordinate system in which the relationships I proposed might be correct.

What’s important here is not the *absolute* values of distance, speed and acceleration, it’s the relationship of relative values as a function of time and density as perceived in the distinct frames of the emitter and observer. Surely one or both of those frames has some special logical relevance to the issue of observed redshift.

Geraint, your papers refer frequently to superluminal recession velocities, which you say are inevitable and open ended at large distances in both the FLRW and conformally Minkowski metrics. You also apply Gauss’ Law in your radar ranging paper in the same manner I do, and you specifically apply it to round-trip velocities in your two selected coordinate systems. You also specifically state that redshift is a result of a discrete transformation at the observer’s frame rather than an accumulation of infintesimal redshifts en route. The terminology I’m using and the points I’m trying to make are similar to those in your papers, although the particular redshift mechanism is original.

Why not address my specific questions and ideas rather than reciting broad mantras: “There are no absolutes my son … everything is relative… ”

Jon

Lawrence B. Crowell

Sigh – this is a coordinate dependent quantity and so there is no single “correct” answer.

> “Again something is amiss. SNI data tells us that the recessional velocities of galaxies in increasing, not decreasing.”

Dark energy is causing recessional velocities to increase in late times (e.g., since about 7Gy), but it will be many Gy before the are as fast as they were shortly after the inflation era ended. Gravity caused recession speeds to slow dramatically during the first 7 Gy before they turned around and started increasing again.

> “Photons don’t accelerate! Null geodesics might be curved and the photon red or blue shifted, but there is no acceleration of a photon.”

I agree that photons don’t accelerate LOCALLY. But at cosmological distances, their travel speed relative to both the observer and emitter MUST change. Otherwise, how could distant galaxies have been receding at superluminal velocities at the time of emission, yet the photons approach us at exactly c today?

GR terminology such as “spacetime curvature” is all well and good, but we should not slavishly constrain ourselves to use terminology which obscures the fact that something real and tangible is occuring out there. Terminology is here to help us communicate, not to get in the way. When I talk about photons accelerating, I am simply referring to the distance they relocate over some elapsed period of time, as measured from a particular frame of reference. Let’s focus on the substance rather than the terminology.

Jon

Well I can’t say the absorber theory is definitely wrong, but I think it is a fundamental principle of the scientific method that all possible approaches should be exhausted that rely on close-to-conventional physics before radically exotic “new” physics is accepted. Time travel is just inherently too radical, and is not used in any other mainstream physics theory. And the concept of time travel is known to have many theoretical impediments. For example, both the emitter and receiver will move substantial distances during the wave travel period. I don’t see how there’s anything in the theory to accomodate that spatial relocation angles between the past, present and future.

In my humble opinion the closer a cosmology theory is to purely kinematic (with GR gravity of course) the more likely it is to be correct.

Jon