Questions for Shaul Hanany

Learn more about my research In August 2008, Shaul Hanany answered visitors questions about cosmology.

Your Comments, Thoughts, Questions, Ideas

From the Museum Floor's picture

How old is the universe? And how long will it last?

posted on Wed, 08/13/2008 - 11:26am
Shaul Hanany's picture


Our best measurement gives an age of 13.7 billion years since the big bang to ....right now. Well, 'right now' is really any time within plus/minus 100 million years from now.

You may think that an accuracy of plus/minus 100 million years is not so great, but we should really consider that 100 million years is only 1% of 13.7 billion. In other words, we know the age of our universe to within 1% accuracy! Isn't that amazing? Just 100 years ago people had no solid clues about such a fundamental issue, and today we know the age of our universe to within 1%.

We are much less clear about how long the Universe will last. This is primarily because we don't understand the properties of 95% of the matter and energy that we observe in the universe. Without a much more detailed understanding of the properties of this matter and energy it is difficult to predict the future.

Hopefully (less than) 100 years from now, someone will write:"isn't this amazing? just 100 years ago they had no solid clue about such a fundamental question, and now we know how long the universe will last to within 1% accuracy".

posted on Mon, 08/18/2008 - 10:31pm
Joe's picture
Joe says:

What inspired you to pursue a career in science?

posted on Wed, 08/13/2008 - 11:28am
Shaul Hanany's picture

Hello Joe,

I have to say that there was no single moment of inspiration. Since the time I remember myself I was always curious about how things work. The 'why' always intrigued me, as in "Why things are the way they are?".

As I learned more my particular interests focused on physics and specifically the origin (and perhaps fate) of the Universe, and on biophysics and specifically how the brain and consciousness work. At some point I had to make a decision between these two widely divergent disciplines and I chose physics.

posted on Mon, 08/18/2008 - 10:39pm
Adi's picture
Adi says:

How do you fly the balloon?

posted on Wed, 08/13/2008 - 8:17pm
Shaul Hanany's picture

Hi Adi,

Thanks for this good question! (Because It lets me acknowledge the efforts of many people at NASA who work tirelessly to make our balloon flights succeed. )

We only build the scientific part of the payload. Balloon experts at NASA connect our instrument to a parachute and to a huge helium filled balloon. They launch it, monitor its flight, decide when to terminate the flight, and they retrieve the payload and the data. They are members of the 'Columbia Scientific Balloon Facility' (CSBF). Here is the link to their web site When they fly a balloon you can watch its trajectory (including speed and altitude) on the web site!

The collaboration between scientists and the dedicated people at CSBF has produced great science results over the years.

posted on Mon, 08/18/2008 - 10:54pm
Anonymous's picture
Anonymous says:

How do people and or objects percieve time within a black hole?

posted on Thu, 08/14/2008 - 4:17pm
Shaul Hanany's picture


First, I apologize for the delay in responding to your question.

You may have heard that there is a (very massive) black hole in the center of our galaxy. So imagine that we board a train on Earth. The train's last stop would be the center of the black hole.

Our perception of time would not change at any time during this trip, regardless of whether we are inside or outside of the black hole. Our life would appear to us to continue normally, until our unpleasant death, about which we will talk below. So in turns of time perception, all is the same throughout the trip.

Considering only the gravitational forces of the black hole, and not any of the other possible mechanisms for damage, such as strong radiation, or high energy particles, we would be torn apart by the force of gravity. As you get close to the center of the hole the difference in the force of gravity between different parts of your body would be enough to tear them apart from each other. All objects of finite size are eventually torn apart by these forces.

I would not recommend this trip as your next family's vacation...

My colleagues at the University of Minnesota Marco Peloso and Keith Olive helped with this response.

posted on Thu, 08/21/2008 - 3:52pm
Anonymous's picture
Anonymous says:

what is your favoret thing in science???

posted on Thu, 08/14/2008 - 8:10pm
Shaul Hanany's picture

Oh - that is such an intriguing question...!

If you mean - 'what is your favorite topic in science?' I would have to say that it is still my first true loves: the origin of the universe and the fundamental mechanism for human consciousness. Over the years however, I have learned enough about other topics to know that nature is so interesting that almost any topic is pretty cool.

If you mean - 'why do you like science?' then I would say that it is the process of being given a puzzle (=some natural phenomenon that we don't understand), figuring it out (= how it works and why it works the way that it does), and thus learning something new, and many times deep, about the world around us.

posted on Mon, 08/18/2008 - 11:10pm
Anonymous's picture
Anonymous says:

Space is considered to be one of the dimensions, like time. Time has a past and a present. Therefore is it possible to bend space?

posted on Fri, 08/15/2008 - 2:34pm
Shaul Hanany's picture


It is a very un-intuitive, but still true statement, that space can be curved. What does that mean?

It is easy to visualize a curved sheet of paper. This is an example of a two-dimensional object that is curved. Another easy example is a hollow sphere. Clearly, this is a curved two-dimensional object. These examples are easy to visualize because we live in a three-dimensional world and can look onto two-dimensional objects. For a tiny, molecular-size bug confined to living on the sheet of paper it is essentially impossible to understand that her space is curved, because she can't view her space, namely the sheet of paper, from the outside.

In exactly the same way, while it is difficult for us humans to visualize a curved three-dimensional space (because it is difficult to imagine living in a four-dimensional space and viewing our three-dimensional sub-space), this is a physical fact.

Physicists have shown that the space near very massive objects is warped (because of the effects of gravity). Physicists, including my own research has shown that on the largest scale of the universe space is flat. I will leave it to another question, and another response to explain the consequences of flat and curved space.

But before I close I do want to point out that 'past', 'present', and 'future' in regard to the time coordinate, do not relate to curvature. They are labels for the time coordinate, just like -3 cm, +1 cm, and +100 cm label a spatial coordinate.

Makes sense?

posted on Tue, 08/19/2008 - 9:01pm
adam jandro's picture
adam jandro says:

when black holes die out what do they become? and does light passing towards these black holes straighten out?

posted on Sun, 08/17/2008 - 2:42pm
Shaul Hanany's picture

Hello Adam,

They disappear. Poof, gone. You wouldn't know they were there. Light passing near them would not deflect. We call the process 'evaporation', which gives the right feel, just like when a puddle of water evaporates.

posted on Tue, 08/19/2008 - 9:05pm
Ronni and Avigail Amit's picture
Ronni and Avigail Amit says:

Dear Scientist,
We were wondering if the rate of the expansion of the universe is slowing or speeding up?
what does it mean for us?

posted on Tue, 08/19/2008 - 7:16pm
Shaul Hanany's picture

Shalom Ronni and Avigail,

What an excellent question, and so up-to-date!

Speeding up. This is one of the most amazing discoveries of the last ~15 years.

Using observations of exploding stars, and separately observations of the cosmic microwave background radiation we have very strong evidence that the rate of expansion is speeding up. The speed-up is attributed to a type of energy (called 'dark energy') that permeates space and causes the accelerated expansion. Understanding the physical properties and the origin of dark energy is one of the hottest topics in physics today.

What does it meant for us?
Since the rate of the expansion is speeding up, galaxies are receding away from us at an ever increasing rate. Soon (some billions of years from now) some will go outside of the reach of our telescopes. Later (some trillions of years from now) most galaxies that we now find in the universe will have moved out of our observational reach. Our galaxy, and perhaps few others close by, will remain alone in an otherwise empty and dark universe.

How sure are we that this is what will happen? Not very sure. The discovery of dark energy is relatively new. We don't quite understand all the physical properties, and more important origin, of this energy. Perhaps when you will become cosmologists you could figure this out!

posted on Sat, 08/23/2008 - 12:38pm
Kyle's picture
Kyle says:

I was've no doubt heard about the Particle Accelerator in Europe. What are the chances of it creating miniature black holes, and what would happen if it did?

posted on Sun, 08/24/2008 - 4:57pm
Shaul Hanany's picture

Hello Kyle,

Let me start with the bottom line and then give some details: I don't believe that there is any merit to the claims of danger arising from mini-black holes at the CERN particle accelerator in Europe.

I have not seen any credible calculation of the chances of production of these black holes. The mere notion that such black holes can be produced is extremely speculative and relies on space having extra (yet un-observed) dimensions. More importantly, throughout Earth's life time Nature has produced billions of billions of collisions, some of them more energetic then the ones that will be produced by the accelerator in Europe. These collisions were produced by cosmic rays colliding with air molecules in Earth's atmosphere. If these speculative mini-black holes can be produced, they have already been produced abundantly throughout Earth's 4.5 billion years of existence and have not caused any harm.

Take a look at these two web sites for more information

posted on Tue, 09/02/2008 - 9:58pm
deena's picture
deena says:

what kind of equipment do you use to see the radiation???

posted on Tue, 08/26/2008 - 6:25pm
Shaul Hanany's picture

Hi Deena,

There is so much to write about our equipment, I could go on for hours. However, here I will be brief.

It takes us about 4-8 years to construct an experiment from scratch, depending on how complex it is. So you can see - there is a lot of instrumentation involved. Please feel free to visit our group's web site
to learn more and to ask more detailed questions.

We construct a telescope by putting two (or sometimes three) mirrors (made of polished aluminum) at proper relative angles between them so that they focus the radiation. At the focal point we place detectors that absorb the light. These detectors operate a extremely low temperatures, just few tenths of a degree above absolute zero.

The entire telescope and detectors are mounted on a balloon borne gondola and launched to an altitude of about 120,000 ft. This is more than 3 times the altitude in which jetliners fly.

posted on Tue, 09/02/2008 - 8:46pm
From the Museum Floor's picture

What prevents airplanes from flying into your balloons or thier strings?

posted on Thu, 08/28/2008 - 1:02pm
Shaul Hanany's picture

Good question!

The balloons are not tied with strings. The balloon is filled with helium. Helium is lighter than air, so that when the balloon is released it lifts the entire scientific payload to very high altitudes, much higher than the altitudes that airplanes fly. So, no strings (or cables) attached!

You may still wander: (1) can the balloon collide with airplanes as it ascends? (2) how do we get the balloon and the equipment back after the data is collected?

Here are the answers:
(1) Absolutely, it can collide. This would not be pretty because the balloon inflates to a size of approximately a football field!. It would completely engulf the airplane and they would both crash to the ground. This is why NASA coordinate its balloon launches with the FAA (Federal Aviation Administration). The balloons also have transponders, just like airplanes, and air traffic controllers know where they are at all times.

(2) From bottom to top a balloon payload consists of the scientific instrument, then a parachute, then the helium-filled balloon itself. When the flight is over, NASA activates a remote controlled device that separates the balloon from the parachute and tears the balloon. The payload parachutes back to the ground, the helium escapes to space, and the torn balloon falls to the ground. All are later collected by NASA.

posted on Tue, 09/02/2008 - 8:59pm
From the Museum Floor's picture

What is dark matter?

posted on Thu, 08/28/2008 - 1:03pm
Shaul Hanany's picture


Imagine that you enter a long room with iron balls in your pocket. As you walk more into the room you feel that the balls are being pulled in a particular direction. As soon as you toss one of the balls in the air it flies and sticks to one of the walls. You do it again, the same happens. You reasonably conclude that there might be a strong magnet on the other side of the wall, even though you can't see the magnet. If you didn't know anything about magnets, you would reasonably conclude that there is something you can't see, but that nevertheless attracted the balls.

Already some 70 years ago an astronomer named Zwicky noticed that galaxies within a group called a 'cluster of galaxies' (there are many, many clusters of galaxies in the universe) seem to be pulled together by something not visible to his telescope. Since then astronomers have verified this discovery many times over in all observed clusters. They still could not see with their telescopes what is this matter that pulled together the galaxy members of the cluster.

In a separate discovery, astronomers have also found that stars within a galaxy are bound to the center of the galaxy by something not visible to their telescopes. Of course, they have accounted for the force of gravity exerted by all the stars that they did observe, but still a lot of extra stuff was missing.

The reasonable conclusion is that there is matter out there that is not detectable by our telescopes, hence it is 'dark'. This dark matter exerts the gravitational force that would explain how galaxies are pulled to the center of their cluster, and how stars are pulled to the centers of their galaxies.

Today, there is also strong independent evidence from observations of the cosmic microwave background that about 30% of the matter in the universe is 'dark'.

So, have I answered your question 'What is dark matter'? Not really, I have only explained how we know it is out there.

We don't really know what dark matter is. We have theories, though, and we may know for sure within 6 months to a year. A new particle accelerator that will start operating in Europe in a few months may discover a widely anticipated new particle. If this particle is discovered, and it has the correct properties, then our theories as to the source of the dark matter will have been confirmed. This will be a great triumph for our understanding of nature.

posted on Tue, 09/02/2008 - 9:36pm
Anonymous's picture
Anonymous says:

What are you thoughts or comments about the new particle accelerator that just opened? Could the creation of a mini blackhole really consume the Earth? I myself am skeptical, but many people have protested the opening of the accelerator. What do you think?

posted on Sat, 09/13/2008 - 2:41pm
Shaul Hanany's picture


There is no substance to any of the doomsday rumors. All of the doomsday claims have been carefully checked by numerous committees and found to be nonsense and baseless.

However, a scientific report that carefully assesses the issues and thoughtfully debunks the claims is not as interesting to read (and to make news) as a claim about black-holes consuming your neighbor's house. Hence the doomsday rumors have spread more effectively.

In an answer to an earlier question I gave the web sites that lay out the case for why the claims are nonsense. Here they are

posted on Thu, 09/18/2008 - 8:48pm
Madie's picture
Madie says:

How far does the universe go? Does it reach on forever, or does it have limits?

posted on Sun, 09/21/2008 - 2:26pm
Shaul Hanany's picture

Hi Madie,

First, I apologize for the long delay in responding to your question.

As far as we can see, the universe has no limits. This would suggest that the universe is infinite in extent. But there are limits on how far we can see, so we can't say for sure that it is really infinite.

At the moment our telescopes can see out to about 5000 million parsec, which is about 15 billion light years away from Earth. A light year is the distance traveled by light during one year and is equivalent to ~9.5 trillion km or about 6 trillion miles. So 15 billion light years is 90 billion trillion miles away from Earth; isn't that a staggering distance? Within this distance we are not detecting any limits, or boundaries, or hints that space is limited in extent.

But of course, we don't know what happens beyond our current observational reach, so we can't be sure what happens beyond.

posted on Sat, 09/27/2008 - 3:02pm
Anonymous's picture
Anonymous says:

What is, exactly, a Higgs Boson? I've heard about it with the LHC being in the news recently, but I have absolutely no idea what it is or why discovering (or not discovering) it would be important.

posted on Thu, 09/25/2008 - 9:29pm
Shaul Hanany's picture


The 'Higgs Boson' is a particle that we hope to discover at the LHC. It is called a 'Boson' because of the set of properties it is expected to have (which I will not describe here), and it is called 'Higgs' after the theoretical physicist (Peter Higgs) who is credited with showing that the particle is central to understanding many properties of the other particles we already know about (such as electrons, photons, quarks, ...).

You probably know that everything around you is made of electrons, protons and neutrons, and that protons and neutrons are not 'fundamental' in the sense that they themselves are made of quarks. So quarks and electrons are the basic building blocks of nature. (I should point out that there are theories in which the quarks and electrons are made of other particles. Those theories are far from being tested). The masses of the quarks and electrons have been measured to high accuracy. But why do the electrons and quarks have the masses they do? Why not much more or much less massive? Why do they have mass at all?

This is where the Higgs boson comes to play. The particular interaction that the Higgs has with the electrons and quarks generates their mass in the most forward way (although I am not explaining how).

The Higgs is widely expected to be discovered at the LHC because it is the one missing particle that fits our model of the fundamental particles of nature.

It would be a major surprise if the Higgs was NOT found. We would need to re-examine our understanding of the interactions between the fundamental particles of nature.

In some sense the absence of the Higgs would be a more fundamental discovery then observing the Higgs, which on its own would be a substantial discovery.

posted on Mon, 09/29/2008 - 1:55pm