# Physical interpretation of Feynman path integral

#### Feynman

Hi
What is the physical interpretation of Feynman path integral?
Thanks

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#### marcus

Gold Member
Dearly Missed
Feynman said:
Hi
What is the physical interpretation of Feynman path integral?
Thanks
here is one view: it does not have a physical interpretation
because it is a way of calculating a sometimes very close approximation

but nature does not know or care how we calculate
she does something, we dont know exactly how
and we have this way of calculating that gets the right answer

it's like virtual particles---maybe they dont exist in nature but they are good to calculate with

it's like feynmann diagrams: maybe nature doesnt know about them---she doesnt need to because she has her own way of doing things without perturbation series----maybe nothing in nature corresponds to feynmann diagrams---they are useful, tho, for organizing the calculation of a perturbation expansion.

that is just one viewpoint
hopefully someone else will provide a contrasting one

BTW Feynmann, if you havent already I invite you to have a look in this Quantum Physics forum
at the electroweak conversation between turin and zephram.
if zephram answers on this thread it will probably be interesting

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#### Feynman

But I know that the path integral have a physical interpretation but i don't know

#### meldi

hello marcus!
I'm interested by the subject but I didn't find the post of turin and zephram. Can you give me a link please?

#### JohnDubYa

Read Feynman and Hibbs' book "Path Integrals." The introduction should satisfy your curiosity.

#### Feynman

So i don't have the Feynman Hibbs book
So can u tell me about the physical interpretation of the path integrals :@

#### Olias

It relational to the many 'sum-over-history' interpretation also by Feynman.
For instance:The fundamental question in the path integral (PI) formulation of quantum mechanics is:If the particle is at a position q at time t = 0, what is the probability amplitude that it will be at some other position q0 at a later time t = T?

This I took from this good paper:http://arxiv.org/PS_cache/quant-ph/pdf/0004/0004090.pdf [Broken]

If you read through it, you can form your own viewpoint, interpretation is open to a vast number of probibilities, every path has many (integral-able)(connecting) histories!

PS the original paper by Feynman was rejected!

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#### somy

Dear Olias;
I see the link. can you tell me how did dirac observed the action plays a central role???
(also the difference between lagrangian and hamiltonian interpretation)

#### robphy

Homework Helper
Gold Member
You might want to start off reading some of these introductory articles by EF Taylor
http://www.eftaylor.com/leastaction.html
and watching some of Feynman's lectures in Auckland (which became "QED")
http://www.vega.org.uk/series/lectures/feynman/ [Broken]

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#### Feynman

But I think taht the Feynman path integral is a link between the quantum physics and the quatum field theory, but how????

#### marcus

Gold Member
Dearly Missed
meldi said:
hello marcus!
I'm interested by the subject but I didn't find the post of turin and zephram. Can you give me a link please?
hi meldi, sorry I didnt respond earlier, I will get a link to that
electroweak thread in the Quantum Physics forum

here's the part of my post that I think you are responding to:

...BTW Feynmann, if you havent already I invite you to have a look in this Quantum Physics forum
at the electroweak conversation between turin and zephram.
if zephram answers on this thread it will probably be interesting...
the thread begins here:

first Duct Taper says something
then Zephram replies
then Turin says "I would like to hear a little more..."

it is really turins perceptive questioning that elicits the good exposition
that thread is a model of what I wish we had more of

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#### dlgoff

Gold Member
marcus said:
...that thread is a model of what I wish we had more of
Yes indeed. I followed that thread and was fascinated by zephram. Thanks zephram.

Regards

#### JohnDubYa

RE: "So i don't have the Feynman Hibbs book "

Then buy it, or check it out from the library.

#### meldi

thank you very much Marcus!

Staff Emeritus
Gold Member
Dearly Missed
JohnDubYa said:
RE: "So i don't have the Feynman Hibbs book "

Then buy it, or check it out from the library.
I bought Feynmann Hibbs about ten years ago. I can't really say it helped me understand field theory. The book that really made a breakthrough for me (YMMD) was Hatfield, Quantum Field Theory of Point Particles and Strings. This book is pretty useless as a general reference but it is very intuitive, somewhat in the style of Zefram_C's explanations, but with all the math, too.

#### Haelfix

Some of Dyson's original papers on the subject are also informative, and quite readable. It explains the link between canonical quantization and the path integral. So if you understand the former things are well off.

I still love A Zee's book, Quantum field theory in a Nutshell. Its a very quick read, is wonderfully intuitive and quite deep. You pretty much have the path integral thrown at you right from the getgo, and its only a few chapters before its almost fully justified.

#### Feynman

So gentelmen,
How we can interprate for exemple the excat solution of Shrodinger equation for harmonic oscilator by Feynmanpath integral?
which is very complex

#### Feynman

OHHHHH
If i can't buy the book, what i do?

#### Feynman

what is the probabilisitic point view about path integral?

#### Feynman

Please what is the probabilisitic point view about path integral?

#### Feynman

What is the relation between Manifolds and the path integral?
Thanks

#### Feynman

What is the differential geometry role on path integral?

#### jtolliver

Feynman said:
Please what is the probabilisitic point view about path integral?
The probability of travelling from one point to the other is the sum over all paths between them of the probability of travelling along that path; The path integral is basically just that sum over paths.

#### Feynman

So can we consider that the path integral is an integral over manifolds?

#### Feynman

So can we consider that the path integral is an integral over manifolds?

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