Broadcast 3465 Dr. Matthew Caplan

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Guest:  Dr. Matthew Caplan;  Topics:  Stellar Engines, the Caplan Thruster, moving the sun and the solar system, multiple other physics related questions with answers.

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We welcomed Dr. Matthew Caplan to the program to discuss his work on Stellar Engines and what has become known as the Caplan Thruster.  In addition, listeners sent in multiple email questions on a wide array of other physics related topics.  We started our one segment 67 minute program with my asking our guest to provide us with a working definition for the Stellar Engine.

Dr. Caplan began discussing the Stellar Engine by talking about moving a star.  Sort of steering it to where you want the star and its system to go.  Think of a tow for a planetary system.  I asked our guest why one would want to do this in the first place.  Dr. Caplan suggested two possible reasons.  One reason was to avoid dying, He spoke of our sun going supernova in the distant future.  Listen to all of what Dr. Caplan said about avoiding dying.  Dr. Caplan cited a second reason we might want to do move the sun and solar system which would be to expand the solar system.  Once again, listen to all of what our guest had to say regarding this reason for wanting to have a stellar engine to move the sun. 

In describing a stellar engine, our guest talked about a Dyson Sphere which he explained later in our discussion.  One of the main subtopics of this conversation dealt with the amount of energy needed to move the sun which he said would be trillions more energy than exists today.  Dr. Caplan had much to say about the future energy needs for a stellar engine, how that energy might be developed or produced and the source(s) of such future energy.  One thing he said that caught my attention was that all aspects of the stellar engine, including the amount of energy needed for it, were plausible using today's physics though clearly calculations, engineering and advancements were needed over time to actually achieve any of this in real time. 

As a result of email questions, Dr. Caplan described the Dyson Sphere which he said would likely be an engine designed around a solar sail though he did not think the solar sail idea was very effective.  He talked about needed thrust, the possibility of thermonuclear jets, and giant engines based on fusion energy.  With all of this being so very far into the future, Jennifer in Denver sent our guest an interesting question asking him how he actually worked on problems or questions that won't happen for centuries if at all.  Don't miss how our guest responded to Jennifer's question.

Another question that came up dealt with just how close we could come to a target object by moving the sun and the solar system.  For example, say we wanted to visit Proxima B about four plus light years from Earth.  The listener wanted to know how close we could get to the target, Proxima B, without disturbing it by putting our solar system in its sphere of influence or to avoid being disruptive to the target and the target environment.  Our guest said this was an important issue to resolve plus it was an ethical question, especially if life might be involved.  Our guest talked about maximizing the flight rate by turning around to fly backwards or in "retrograde." 

A Portland listener asked our guest for the physical characteristics of a stellar engine, along with how and where one might be made.  He said it would be huge and probably constructed in obit. He talked about an engine hundreds of kilometers in size.  Listen to what he said about it and the relationship with Mercury.  This led to a series of complex questions, starting with a few by Joan, asking about human interstellar flight, limitations, energy from fusion, sleeper ships, biological components and more.  Our guest mentioned so many unknowns, especially about the amount of energy needed to keep a person in hibernation plus the impact on biology and body parts in doing that for years and years.  I asked if a patient in a coma or a medically induced coma was a good analog for a study of potential long term human spaceflight hibernation effects.  Should listeners have experience with comas and the biology of a person plus energy usage in a coma, perhaps you can share some of your expertise with us on the blog.

Stellar engine energy needs kept returning as a major part of our discussion.  At one point, Matt talked about the idea of dismantling a start to extend its life by breaking it up into smaller components that consume less energy over time, thus the star would be smaller, less bright, but it would live for a significantly longer period of time.  For sure don't miss this discussion and this concept.  We also talked about early Space Show guest, a great physicist who has now left us, Dr. David Criswell from the University of Houston, and his work in this area.

Listener Brandy got in an off topic question about time travel.  Our guest talked about going forward in time but not backward.  Listen to all of what was said about the time travel question.  Just before time travel was discussed, Carol asked about consciousness and the possibility of our transferring our consciousness to the virtual state.  Our guest said that while we have no way to do that, the physics does not make it an impossible technology.

Alexander in Dallas asked about the modern teaching of physics.  Given much of what we talked about was rooted in decades old or centuries old physics from many of the greats we all study, he wanted to know how fast the teaching of physics was evolving, especially for the classroom.  This was an interesting question because to understand going forward, one must really know the past which is the foundation for modern physics.  Don't miss what our guest said in response to this questions.  What do you think of the examples cited in his response?  We ask you to post your comments on our blog.  Don't miss what our guest said about funding, social presence and give and take.  Before the program ended, Matt was asked about quantum computing. He said it was not his field, that he used daisy chains of more or less regular computers for super computers but thought quantum computing would expand and become more and more important in the future. 

To find out more about  Stellar Engines, you should read Dr. Caplan's paper, "Stellar engines: Design considerations for maximizing acceleration."  The paper is dated Dec. 2019 and is in Volume 165, Pages 96-104 of Acta Astronautica.  Read the abstract at  If you do a Google search for Stellar Engines and Dr. Matthew Caplan, you will find lots more information with articles and interviews to help you understand the importance of stellar engines and the why of the work going on to help create them.  We will ask Dr. Caplan back to talk more about stellar engines in the future.

Please post your comments/questions for this program and guest on our blog for this show.  You can reach Dr. Caplan at his faculty page at





Dr. Caplan talks about his work on stellar engines

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21 Feb 2020 Dr. Matthew Caplan
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