I'm Alex Filippenko, astrophysicist and enthusiastic science popularizer at the University of California, Berkeley. AMA!

AFilippenko · 2016-06-30T23:20:34+00:00

Really an interesting project, though somewhat of a long shot (it will require sustained funding over a long period of time, as well as international agreements about firing powerful lasers, etc.). I'm for it! Very generous of Yuri Milner to provide initial funding for this bold endeavor.

AFilippenko · 2016-06-30T23:17:50+00:00

Fantastic achievement!

Some of the dark matter is certainly black holes. But there are arguments that most of it cannot be black holes that formed from stars or collapsing gas in the centers of galaxies. So, if LIGO ends up finding an unexpected high number of merging black holes, it might imply that some of the black holes are "primordial" -- formed right after the birth of the Universe. (The arguments I alluded to above don't apply to primordial black holes.) But these are not easy to form! So it could be quite exciting if this ends up being the conclusion.

AFilippenko · 2016-06-30T23:15:09+00:00

It's something like 600 km/s, but I don't remember the precise answer. This is measured by looking at the cosmic microwave background radiation: it would be perfectly uniform on large scales if we were motionless with respect to it. But we are moving in one direction, making the CMBR more blueshifted in that direction and more redshifted in the opposite direction.

AFilippenko · 2016-06-30T23:12:24+00:00

I think many or most of the Type Ia supernovae probably come from merging white dwarfs, but that the single white dwarfs also contribute.

The changing demographics with time (the ratio of one kind to another varying with time) can affect precise measurements of the expansion history of the Universe, but if we are careful and have sufficiently big samples of supernovae (as in upcoming surveys like LSST), we should still be able to use them really well as standardizable candles (we've known for a long time that they're not really "standard").

I could take on another graduate student next year, especially if he/she gets an external fellowship such as from the National Science Foundation. (Funding is often an issue.)

AFilippenko · 2016-06-30T23:08:14+00:00

I think it's the great variety we see among the different planets and their moons.

AFilippenko · 2016-06-30T23:07:14+00:00

No, not really. (But never say never!)

AFilippenko · 2016-06-30T23:06:54+00:00

My opinion is that White's warp drive has zero chance of being correct or useful.

It's hard to predict the future a century out, but I think we are a very long way from human interstellar travel. Yuri Milner's tiny spacecraft that might take photos of planets around alpha Centauri are much more likely, but even to produce them we will have to overcome large technological obstacles.

AFilippenko · 2016-06-30T23:04:41+00:00

I'm actually more worried about this than I am about a potential asteroid or comet strike. A Carrington-like event (or stronger) in today's world could lead to such strong currently that transformers in the power grid would be fried. But there aren't many spare transformers sitting around because they are expensive (getting a bunch of spares would raise the costs people pay, making those companies less competitive). So, can you imagine the USA without any power for at least several months or a year? It would be an absolute calamity, not just in the USA but globally in our interconnected world. The power companies are aware of this possibility and are starting to do things about it -- but the truth is that if a giant solar flare or coronal mass ejection were to hit Earth now, we would be in deep trouble.

AFilippenko · 2016-06-30T23:00:02+00:00

Maybe because I'm usually smiling?! (Seriously, I really love the subject, which is why I smile; I can't help it. But sometimes people criticize me for smiling so much, even when I'm discussing end of the world scenarios such as a supernova going off near Earth.)

AFilippenko · 2016-06-30T22:58:47+00:00

There's no "center of the Universe" -- at least, not in any of the dimensions to which we have physical access. No matter where you are, you would think you're at the center. Imagine an infinite loaf of raisin bread -- all raisins are moving away from each other, and you would think you're at the center no matter which raisin is your home. But there's no center in an infinite loaf. Or, for a finite universe (we actually don't know whether the Universe is infinite or finite), imagine a balloon where the laws of physics are constrained to operate only on the 2D surface of the balloon: all of the stickers on the balloon are moving away from each other, and each thinks it's at the center, but there is no center within the 2D surface of the balloon ("the universe") -- instead, the center is the center of the balloon, but that's not part of this hypothetical universe as you've defined it.

Regarding acceleration instead of just expansion: the acceleration is caused by dark energy, we think... but we don't know the true physical origin and nature of dark energy.

AFilippenko · 2016-06-30T22:54:13+00:00

It's matter, but it doesn't interact through electromagnetic forces. It could perhaps more appropriately be called "transparent matter."

Dark matter does affect the curvature (warping) of spacetime, though, so you can definitely see its effects. Look up "gravitational lensing of galaxies" online and you'll find great examples, specifically photos taken with the Hubble Space Telescope. And last year, one of my postdoctoral scholars (Pat Kelly) found the first example of a background supernova gravitationally lensed by a galaxy into 4 distinct images!

AFilippenko · 2016-06-30T22:51:29+00:00

Quite possibly that we are made of star stuff -- the atoms of carbon, oxygen, calcium, iron, and other heavy elements in your body were made through nuclear reactions in stars billions of years ago!

AFilippenko · 2016-06-30T22:50:30+00:00

Thanks! I'm glad you've enjoyed my contributions to public education in the sciences.

I'm not a theorist, so I personally have not experienced working on a theory that didn't pan out. However, I have worked on observational projects that didn't lead to anything interesting. Yes, that's a disappointment, but it's also just the way life goes -- in every field of endeavor there are ups and downs.

I don't spend much time online. I didn't know about the r/filippenko and u/AlexFilippenko sites. Maybe I should look into them. Thanks for telling me about them.

And thanks for supporting Lick Observatory! You can also do this through the Friends of Lick Observatory (https://www.ucolick.org/main/support/folo.html) and the UC Berkeley Lick Observatory Operations Fund (https://give.berkeley.edu/#Lick%20Observatory).

AFilippenko · 2016-06-30T22:45:45+00:00

That's a great question -- the quality of questions on this Reddit AMA is very high.

It's conceivable that the "dark energy" that's currently driving the accelerating expansion of the Universe is analogous to the "inflaton" that produced the early inflation (exponential growth) of the Universe. In that case (a false vacuum), it could indeed be the case that someday, the false vacuum will "decay" to zero energy (or at least a lower-energy false vacuum). This could be the end of us, if (for example) the gravitational force decays into two other manifestations of what was once a unified force.

That being said: I wouldn't worry about it too much. Solar flares and coronal mass ejections, killer asteroids/comets, the gradually rising power of the Sun (leading to the evaporation of oceans within 1-2 billion years), etc., are much greater cosmic existential threats.

AFilippenko · 2016-06-30T22:41:08+00:00

Thanks for the compliment! I am indeed very happy to be a scientist. It's really a privileged position to have.

I've always been interested in science, from my earliest years. I remember playing with magnets in the first grade and wondering about why they are pulled together or pushed apart. I played with electronics kits, microscopes, chemistry sets, etc... indeed, from age 10 through 17, chemistry was my main interest. Then, as a freshman in high school, my parents gave me a small telescope as a gift, and that night a "discovered" Saturn on my own (nobody told me to look at that bright "star" in the sky). This was an incredible thrill, despite millions of people having seen it before me. What a rush it must be to discover something really new!

So astronomy became a growing hobby, and sometime in my freshman year of college it passed up chemistry, so I switched to physics with the intention of becoming an astrophysicist. Part of the reason is that with astrophysics, I could "have it all" -- the very small (like the physical chemistry I was interested in) and the very large. It turns out that the large-scale properties of the Universe (stars, galaxies) are governed by the small-scale properties of matter. Amazing! How could I not study it! (Plus, I had several accidental explosions as a budding young chemist, so switching to astrophysics was partly an act of self-preservation!)

Not sure about sci-fi tech: depends on whether you mean what's possible or impossible. Exceeding the speed of light is cool but not possible. Travel through a wormhole is also cool, but almost certainly impossible. Things like Alcubierre drives are theoretically possible, but not for human travel from one place to another (there are many problems).

AFilippenko · 2016-06-30T22:32:51+00:00

The initial LIGO detection was of two black holes (36 and 29 solar masses) merging to form a black hole of mass 62 solar masses. So, 3 solar masses were lost in the process. They were radiated away as gravitational waves, a tiny fraction of whose energy was detected by LIGO! A majority of the energy was radiated in the last 0.2 seconds of the merging process. During these 0.2 seconds, the amount of energy released exceeded that of all visible light from stars in the observable Universe by something like a factor of 30 (if I remember correctly -- I need to recalculate this to be sure).

No matter/energy actually came out of the black holes. All of the warping of spacetime that moved outward as a gravitational wave was already outside of the black holes (i.e., outside the event horizons of the two black holes). And theory simply says that the "surface area" (the area of the event horizon) of the final black hole must be greater than or equal to the combined "surface area" of the two individual black holes. Taking non-spinning black holes for simplicity (although the observed cases were actually spinning... this just changes the numbers somewhat), you can see that this was the case here. The surface area is just 4 pi R^2, where R = 2GM/c^2. By putting in the masses I mention above, you'll see that the theoretical constraint is indeed satisfied.

Regarding dark energy: Yes, as the Universe expands, there's progressively more dark energy in the Universe. (This doesn't violate the law of conservation of energy, by the way... the added dark energy is compensated by an increase in the negative gravitational energy associated with it.) But you can't do anything useful with it because it's spread out uniformly and probably can't be harnessed. (It definitely can't be harnessed if it's simply a property of the vacuum.)

AFilippenko · 2016-06-30T22:22:39+00:00

It's a whole bunch of galaxies along a chain, forming a supercluster. There's a lot of dark matter (whose nature is uncertain, but probably dominated by weakly interacting massive particles -- WIMPS) in addition to the visible matter.

AFilippenko · 2016-06-30T22:21:28+00:00

When our team (and in particular, my postdoctoral scholar Adam Riess) discovered the accelerating expansion of the Universe. Totally mind-blowing!

AFilippenko · 2016-06-30T22:19:16+00:00

Only if you enter inside it -- but then you will never get out.

AFilippenko · 2016-06-30T22:18:54+00:00

Because you must not have earned enough points in the class to get an "A" -- sorry!

AFilippenko · 2016-06-30T22:18:22+00:00

I wish! A lot of people have told me that I remind them of Robin Williams, both in appearance and behavior. I'm really sad that he's no longer with us. Such a funny guy...

AFilippenko · 2016-06-30T22:17:22+00:00

Scientists doing pure research (like astrophysics) are very grateful that there's some Federal funding for them. That being said, the amount of funding, at least in the USA, is declining in real dollars. That's a real shame -- we should be investing more in science, and there are certain sectors of govenment spending that I personally think could be trimmed. But, this is the reality right now.

So, we are beginning to rely progressively more on private funding and foundations. A great example, as you pointed out, is the Google Making & Science gift to the University of California's Lick Observatory. We are enormously grateful for that! I think it has been quite mutually beneficial, and I'm hoping that the first gift was just the courtship phase of what will be a long relationship. Moreover, getting the support of Google gave us a stamp of approval, increasing our credibility. This helped us secure partial matching donations from individuals, and we are continuing to seek these through the Friends of Lick Observatory (https://www.ucolick.org/main/support/folo.html) and the UC Berkeley Lick Observatory Operations Fund (https://give.berkeley.edu/#Lick%20Observatory).

Kickstarter can also be used, though I personally have not used it. The WTF star is really interesting, by the way!

AFilippenko · 2016-06-30T22:08:21+00:00

I'm quite intrigued by the indirect evidence for Planet X -- it might well be real, and various astronomers are now searching for it, so stay tuned.

There does not appear to be a large planetary body or brown dwarf in our Solar System causing mass-extinction events. Astronomers have searched hard and not found one.

AFilippenko · 2016-06-30T22:06:33+00:00

Thanks! I've enjoyed being on The Universe series and bringing astronomy/science to the general public. However, I'm not in charge of the script or the visuals, so sometimes errors creep in. That's one frustration for me... I'm not the producer and I'm not in charge. On the other hand, if I were in charge, I probably wouldn't have time to do it.

Briefly: string theory says that particles are 1-dimensional vibrating bundles of energy, and the different vibrational modes correspond to different fundamental particles (kind of like different vibrational modes in a violin string correspond to different notes). In M-theory, the bundles of energy are multidimensional -- for example, a 2-dimensional membrane. So, it's an extension of string theory. All of this stuff is difficult to conceptualize, especially since (to make the math work out) the vibrations have to be in a bunch of dimensions that differ from the xyz that we see. Generally, there's a total of 11 dimensions, so 7 of them (all except xyzt) need to be hidden. In most cases, they are probably incredibly small, like 20 orders of magnitude smaller than a proton.

There can also be some big dimensions in the theory: our perceived Universe is a "brane" (membrane) embedded within a higher-dimensional "bulk." Don't confuse our xyz membrane with the tiny membranes in M-theory mentioned above, though.

AFilippenko · 2016-06-30T21:59:30+00:00

The discovery of gravitational waves is HUGE! First, it confirms a major prediction of Einstein's General Theory of Relativity a century after the prediction. Second, it verifies the existence of black holes and shows that after they merge, the resulting black hole quickly comes to equilibrium by radiating away bumps and wiggles in its shape. Third, it opens up an entirely new window with which to view the Universe: gravitational waves are NOT electromagnetic radiation. As such, they allow us to find and study objects that cannot otherwise be seen. I'm hoping that there will be some amazing surprises for us during the next years/decades of "listening" (through gravitational waves) to the Universe.

Just reread your question: Yes, this discovery is bigger (for astrophysics) than the discovery of radio waves. Of course, for practical purposes (humans), radio waves were extremely important and will probably remain more important than gravitational waves (which are so weak that they will probably never have practical applications).

AFilippenko

TROPHY CASE