Ask physicist Brian Greene anything

Last week, physicist Brian Greene answered a lot of questions—including a few submitted by BoingBoing readers!—at a live event in New York City. If you missed it, you can watch a recording of the event online now.

But wait, there's more! Dr. Greene only had an hour to talk, and a metric crap ton of very good questions—including, again, some from BoingBoing readers—went unanswered. That's why I'm pleased to announce that the World Science Festival has added a new column to their website, called Ask Brian Greene Anything. For the next month, he'll be sifting through leftover questions from the live event as well as new submissions to answer a physics question every day.

Here's the latest:

Q: If nothing can travel faster than the speed of light, then how did the universe become so big and vast in the blink of a micro-second during the big bang? — Carlos Cordoba, Queens, NY

A: You have to be a little careful when invoking the notion that “nothing can travel faster than the speed of light.” Einstein’s special theory of relativity actually shows that nothing can move through space at a speed greater than light speed. But the process that makes the universe “so big and vast” does not involve objects moving through space. Instead, it arise from the swelling — the expansion — of space itself. And nothing in special relativity constrains the rate at which space itself expands. Indeed, in the early moments of the universe, the expansion of space can rightly be said to have exceeded the speed of light, meaning that regions of space were driven apart via the expansion at a greater-than-light speed. Moreover, since the expansion of space is cumulative (the farther apart two points are — the more space there is between them — the faster they rush apart as space expands), even today there’s a sense in which sufficiently distant regions are receding from each other at a greater-than-light speed.

Also, an important reminder: Reader Kevin Harrelson needs to email me in order to claim his free DVD set of Brian Greene's new NOVA series, "Fabric of the Cosmos." You can reach me at

Image: Dark and ordinary matter in the Universe, a Creative Commons Attribution Share-Alike (2.0) image from argonne's photostream


  1. Wow, this is terrific!  Thanks Maggie!   I love to see so many others interested in physics and to read their insightful questions (and to see Dr. Greene’s responses).   Seriously, I dig this stuff!

    OK, EH, it’s not Brian Austin Greene — he’s too busy with Megan Fox to think about science.

    1. ZG, if you mean the mathematical problem of giving infinitesimals a rigorous foundation, that was done 50 years ago.

  2. Interesting stuff, but this is not watchable for the bandwidth-impaired among us. Does a transcript of the session exist somewhere?

  3.  So, if space is expanding at such a rate that two distant points are moving faster than the speed of light relative to each other will the radiation from one point be red shifted to negative frequencies, or will it just never get to me if I am at one of the two points and the radiation source is at the other? I know this question sounds like nonsense as frequency is a scalar, and thus cannot have a negative value. But don’t they sometimes talk of Dark Energy as negative energy? When Spock said the Space Amoeba created a zone of negative energy, I balked because energy is scalar, and thus cannot have a negative value. I am not a physicist, but I have generally understood that only vectors can have negative values.

    Am I totally wrong about vectors and scalars? And if the radiation from some parts of the cosmos simply disappears relative to other parts of the cosmos, where does it go?

    Is it just me or does the whole Big Bang model seem to be falling apart? Sure, we’re modifying it with inflations and dark energy. but I expect Cosmology will be making a call on Drs. Kuhn and Lakatos very soon. I can’t wait to see what happens.

    BTW, saying the Big Bang model is falling apart does not make me a creationist sympathizer.  Just gotta put in that disclaimer.

    1. The latter: if expansion does not slow, then light emitted from a point receding at greater than C will never reach us. No exchange of information, no causal connection, no way to get there. From our perspective, such places literally may as well not exist.

      btw, inflation has been part of the BBT from the beginning. In fact, that’s pretty much what BBT is.

  4. Isn’t universes just popping out of nothing kind of nothing kind of er… miraculous? Does conservation of mass and all that not apply to universes?

  5. Isn’t infinity really a guess? My father told me years ago that the numbers of stars were infinite. Years later I saw a shooting star, he told me it was a star that died. I asked him how can you have one less of infinity. If one dies, that’s one less,  if one’s born, that’s one more.

    Question: Are the words “one, born, died” are any other relating to measurement, true in the realm of infinity?  If anything is infinite, then there wouldn’t be room for anything else. 

    I call B.S. on infinity, I think it means someone doesn’t have the answer.

    1. Because if a star dies you don’t have one less than infinity.  There is still an infinite  number of stars.  You have one less star in a finite subset of stars.  

  6. Here’s a nagging question:

    Time slows down wherever there’s mass or speed, check.
    The greater the mass or speed, the slower the time, check.

    But let’s say time slows down by half at the edge of an event horizon, while time keeps on flowing “normally” elsewhere.  So it seems that while they say “the universe is 13.7 billion years old” from our vantage point, at the edge of an event horizon only 6.85 billion years have come to pass.

    Also, the most distant visible galaxies are super red-shifted from our vantage point, but that’s a two-way street, the Milky Way is also receding at an equal rate from “their” perspective, so surely our time is slowed down.

    How have we factored in all this relativistic complexity, to determine a precise span of time since the Big Bang?  Or even weirder, is there such a thing as a standard time, or meta-time?

  7. When you exclaim, “SCIENCE!,” do you do it with your hands on your hips or with one finger pointing off into the distant future?

  8. If dark matter is attracted to normal matter by gravitation, then by what mechanism is it segregated from normal matter in galaxies and galaxy clusters? If dark matter obeys the laws of gravity, shouldn’t we find it everywhere that we find normal matter? Shouldn’t it be evenly mixed into local matter in our galaxy, solar system, and breakfast cereal?

    1. Maybe I can answer this question, my understanding is that:

      Ordinary matter would be everything that’s made of quarks and leptons, and responds to the four basic forces in the Universe:  the Strong Force, the Weak Force, Electromagnetism and Gravity.

      Dark matter (the WIMP type, Weak Interactive Massive Particles) only responds to and interacts via Gravity.  Since dark matter does not bind with itself or ordinary matter, it can never be solid, all it can be is a vast fog of loner particles.

      For matter to be detectable by our senses or instruments, it needs to emit, absorb and/or reflect radiation, that’s what quarks and leptons do.  But no matter how intense a beam of photons you throw at dark matter, none are ever going to bounce off, they’ll just whiz by;  at the quantum level, it’s like there’s nothing there at all.  Dark matter is all around us, even in our breakfast cereal, but we have no way of detecting it firsthand.

      If I’m mistaken in the concept, hopefully a fellow BBer could point it out.

Comments are closed.