# Breakthrough Panel Discussion on Time Travel

Everyone seemed to love the panel discussion on "Is time travel possible?", featuring Veritasium's Derek Muller as host; and Nima Arkani-Hamed, Daniel Harlow, Daniel Jafferis, and myself as panelists. We had a lot of fun with it, but also there's some profound physics involved, in what one might have thought was a pretty flippant choice of topic. So without further ado, here it is:

(Back up to 7:55 if you want to hear all the introductions to the event at the beginning.)

After our panel there were two others on "What are the limits of Science" and "Is there life in the Universe", recorded in the same video. There were a lot of interesting people on these panels, although I don't think the conversations cohered quite as well as ours did, perhaps because they involved people from different disciplines.

In the second panel, Andrei Linde is a fun speaker, but I think he overplayed how much we currently know for sure about the early universe after inflation happened. There are a lot of mysteries between the time inflation ended (about $10^{-35}$ seconds after the Big Bang by his reckoning) and the time of the Higgs Phase Transition (about $10^{-12}$ seconds, which corresponds to the highest energy scale we can measure at the LHC). Between these times there are a lot of mysteries, like what process produced more matter than antimatter, as needed for any matter to exist today. I also wish he'd mentioned Cosmic Variance, a pretty obvious Limit on Science in his field.

Gary Ruvkin, the guy who thinks life on earth came from outer space was also kind of interesting. Apparently after about a billion years of nothing, life shows up on Earth and it's already pretty complicated. So maybe it came from elsewhere? The downside of this hypothesis, he said wittily, is that it "only buys you another 10 billion years" to evolve life (going back to the Big Bang). Since this is a physics and theology blog, I'll mention that even though I generally think that Darwinian evolution suffices to explain the evolution of complex life from simpler life, it does seem bewildering how something as complicated as the first cell might have arisen naturally, without a miracle. But just because I can't imagine it doesn't necessarily mean it couldn't have happened by some natural process. As a theist I am philosophically open to both supernatural and natural explanations, both of which are ultimately due to the Creator of all things.

That third panel should really have been: "Is there other life in the Universe", otherwise I think the question is pretty easy. This panel includes Jocelyn Bell Burnell who received a special Breakthrough prize this year for her revolutionary discovery of pulsars. Scandalously, the Nobel was given to her advisor but not to her; either because of sexism, or because of a bias against graduate students, or some combination thereof.

This seems like a good time to mention that, if I understand the history correctly, it was Daniel Jafferis' grad student Ping Gao who had the original idea to try to make a traversable wormhole in AdS/CFT. (Although as the 3rd person to join the collaboration, I can't speak to the exact division of labor between Ping and Dan.) Now the New Horizons prize was awarded for our lifetime of work so far, and not just for this one article, so I'm not saying that Ping should have been eligible for this particular prize. But I do think it's important for people to acknowledge junior collaborators, and not just assume the senior people did all the best work. So thanks Ping!

[Apparently I misunderstood the history, and is was Daniel who had the original idea and assigned it to Ping as a project.  I apologize for the mistake, but of course I'm still grateful to Ping for his hard work and insights!]

## About Aron Wall

I am a Lecturer in Theoretical Physics at the University of Cambridge. Before that, I read Great Books at St. John's College (Santa Fe), got my physics Ph.D. from U Maryland, and did my postdocs at UC Santa Barbara, the Institute for Advanced Study in Princeton, and Stanford. The views expressed on this blog are my own, and should not be attributed to any of these fine institutions.
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### 5 Responses to Breakthrough Panel Discussion on Time Travel

1. J Cook says:

Would it be so terrible there was no other conscious life in the universe

2. Andrew Wells says:

That’s sounds like a really interesting panel video, I’ll def. give it a watch sometime this week.

On one thing you did mention here though, about the origin of life. Stephen C Meyer wrote a really good book on the subject, Signature In The Cell. I’m sure you may’ve heard of it as it created quite the controversy. I wrote the tl;dr synopsis of his argument against chance here:

https://paperpandao1o.blogspot.com/2018/08/what-really-matters-in-search-for.html?m=1

By chance alone the process is virtually impossible, as virtually every biologist agrees (according to Ayala’s review of the book), but Meyer goes on to critique “physical necessity” and “necessity and chance” as explanations as well. I’m not expert and I think biological evolution is a pretty good theory but I find his argument against chemical evolution really tempting.

3. Aron Wall says:

Andrew,
Thanks for the link. But I think that phrasing things in terms of "chance" versus "necessity" is not exactly the right way of thinking about things. As you say, nobody believes that complex proteins formed by pure chance. The question is whether there can be a physical explanation, e.g. much simpler molecules that were still capable of self-reproduction (in some environmental context), which then developed additional complexity by some evolutionary process. (And then perhaps jettisoned its original method of copying information in favor of a better one---this is a point that evolutionary skeptics don't usually address.)

Note that these simple molecules would not have to be similar to modern day life, nor would they necessarily have to be viable in today's environment. Since this is an open scientific problem, nobody knows whether this is possible or not.

4. Chris says:

Hi Dr. Wall,
I have a question about a paper you published a long while ago in support of the universe having a beginning. You wrote a paper called "The Generalized Second Law implies a Quantum Singularity Theorem" that I found quite persuasive (especially when taken in context along with things like the BGV theorem). However I have recently read an article called, "Quantum no-singularity theorem from geometric flows" - (arxiv.org/abs/1705.00977 ) . This article doesn't directly interact with the BGV as far as I can tell, but addresses the Hawking Penrose one and concludes that quantum space-times are complete. It seems to contradict your paper and was curious what you thought of it; as well as the current state of research about whether or not the universe is past finite (finite even if it lacks a singularity)?
Thanks,
Chris

5. Phillip Mac says:

This gives me a feeling there is a lot to understand and more to be discovered in the world we live in considering theories on understanding life are more than facts discovered about life starting with illogical facts of time travel though it's exciting seeing it being worked out