Start a new word processing document that contains your entire physics book, including the title page with your name, a dedication page if you choose to have one and a table of contents. A bibliography listing all of your references should follow the final chapter. Keep the format simple as you will most likely be cutting and pasting.
Find a self-publisher online and read their guidelines carefully, as there are dozens available, each with different prices and packaging options. Look at Lulu and Infinity Publishing to get an idea of what self-publishers have to offer.
Register with the self-publishing company and enter or upload your physics book through their online form. Proofread and edit your book carefully, as you will most likely not be working with an editor (unless you choose to hire one). Citing research and case studies is important in giving a physics book credibility, so take care to include in-text citations as you enter.
Check the proof copy the publisher sends you, and if possible, have a few colleagues read it as well before ordering your copies from the publisher.
Write your proposal package for submission to literary agencies. Your submission consists of a detailed chapter-by-chapter outline of your physics book, the first two or three chapters, and a professionally written biography that establishes you as an expert in the field. Agents and editors will normally not consider taking on physics books unless the author has a platform; in other words, an established presence in physics as it relates to the topic of the book.
Find a literary agent on Publisher's Marketplace or Agent Query that represents non-fiction books, specifically those in the field of science. Compose a query letter, which is similar to a cover letter and should introduce you and your physics book, along with any marketing ideas and information about your target audience. If possible, compare your book with others already published, but be sure to state what yours has to offer that others don't.
Follow each agent's specific guidelines because they will vary slightly, and send your query and submission package. After signing with an agent, set a strategy for finishing and editing your physics book. Your agent will compile a list of editors to whom you should submit your manuscript, and also help you negotiate your future contract.