The Impossible Is Still Impossible

I saw this article in Wired referenced on a couple of science pages on FaceBook. 

NASA validates 'impossible' space drive

Let me give you the short version of how this engine is supposed to work. Microwaves are beamed into a cone-shaped cavity. They bounce around the cavity and produce a force on the cavity in a direction perpendicular to the direction they were beamed in. Imagine  turning on the microwave oven and watching it push itself off the kitchen counter.

Why is it impossible? This violates one of the basic laws of physics. 

The Conservation of Momentum

The conservation of momentum isn’t your ordinary law of physics. It is one of the most fundamental principles in science. It is intimately related to spatial symmetry. Roughly speaking, the laws of physics here are the same there. You may know this as Newton’s third law of motion or for every action, there’s an equal but opposite reaction.

To obey the conservation of momentum, propellent is pushed out by the rocket and the rocket is pushed by the propellent. This engine is said to produce thrust without any propellent. 

So I was immediately skeptical. So I dug around a little bit. I found a short description of the experiment. One thing I found interesting is that the authors did not lecture on “”physics of the quantum vacuum plasma thruster.” All right, that’s fine; if the results were groundbreaking, the explanation might come later. Something similar happened in 1986. Researchers at IBM discovered ceramic materials that lost all electrical resistance (superconductivity) at surprisingly high temperatures. There is still no complete explanation for why this happens. What is different about these two cases is that the superconductivity ceramics didn’t violate any basic principles of physics.

What made me laugh however is the authors claim that their device may be “demonstrating an interaction with the quantum vacuum virtual plasma.” I have no idea what they mean by a quantum vacuum virtual plasma. 

I also found their paper. This made me giggle, too. They built two devices: one was designed to work, the other was designed not to work. Both versions produced the same amounts of thrust.

Phil Plait in his Bad Astronomy blog at Slate says this episode is reminiscent of the faster than light neutrinos and the mysterious force slowing down the Pioneer spacecrafts.

It reminded me of an article that caught my attention while I was in grad school. I remember getting all excited about this revolutionary paper published in one of the premier physics journals. The authors had data that showed that a gyroscope rotating in one direction weighed less than if it were rotating in the opposite direction. Finally, an anti-gravity device!

My research advisor wasn’t nearly as excited. His comment was something along the lines of “systematic error.” But still I held out hope.

Then four months later, my anti-gravity hope were dashed. Others trying to replicate the results found there is no anti-gravity.

Baby Pictures

A baby picture of the universe!

http://www.nasa.gov/mission_pages/planck/multimedia/pia16873.html

This is a map of the cosmic microwave background (CMB), the leftover radiation of the Big Bang, made by the Planck mission of the European Space Agency.    This light was emitted when the universe was 380,000 years old. 

There's a number of AWESOME results here.

1. The colors represent small fluctuations in the temperature of the radiation, about 1 part in 100,000 or 0.001%.  Since the average temperature is a mere 2.73 K (2.73 degrees above absolute zero), the fluctuations are roughly 0.00003 K.  To put this in perspective, imagine setting your oven to 350ºF and it never varies by more than 0.008ºF.

2. This light was created just 80,000 years after the universe was cool enough for neutral hydrogen atoms to form.

I couldn't find any baby pictures,
but here I am when I'm about
10% of my current age.

3. It provides the best estimate for the age of the universe.  13.82 billion years.

4. The universe is 4.9% normal matter (protons, neutrons, and electrons for the most part.) Dark matter makes up 26.8% and dark energy 68.3%.

5. The universe is amazingly uniform, isotropic in the physicist's lingo. But there is a tiny difference in the size of the fluctuations in one half of the sky as compared to the other half.  Intriguing!

6. This picture represents the universe when it was just 0.00002750 of its present age.  Let's compare this to one of my students who say is 20 years old; this student was only 5 hours at 0.00002750 of 20 years.    

Is Your Cell Phone Killing You?

It could, if you're texting while driving.

My least favorite TV physician, Dr. Oz, says on his website that "experts have grown concerned about the health implications of heavy exposure—specifically, the radiation that the devices emit." Dr. Oz often offers misleading advice, but this is just plain wrong. Experts know that there is no danger from cell phones.

 The World Health Organization (WHO) reports that "[a} large number of studies have been performed over the last two decades to assess whether mobile phones pose a potential health risk. To date, no adverse health effects have been established as being caused by mobile phone use."

 The National Cancer Institute at the National Institutes of Health says "there is no evidence from studies of cells, animals, or humans that radiofrequency energy can cause cancer."

 What is it about cell phones? Cell phones use microwaves - a form of electromagnetic radiation. The history of this issue goes back at least to an article in the New Yorker in 1989. Paul Brodeur alarmed the country when some epidemiological studies supposedly showed an increase in cancer in homes near power lines. [More about epidemiology later.] The power lines as all electrical currents generate magnetic fields - extremely low frequency radiowaves. Scientists never found any causal link. In fact, when more careful epidemiological studies were conducted, the correlation between exposure to electromagnetic fields and cancer disappeared.

Now for the science lesson. Cancer is an example of a biochemical reaction gone horribly wrong. While not well understood in many types of cancer, whatever happens causes the uncontrolled growth of abnormal cells. Documented cancer-causing agents are perchloroethylene (used in dry cleaning), tobacco smoke, ultraviolet light, viruses, and environmental toxins like aflatoxin in peanut butter.

How can light (electromagnetic radiation) cause these biochemical changes? Each particle of light called a photon has an energy that depends on the color of the light. As one can see from the diagram, light comes in more colors than just red. orange, yellow, green, blue, indigo, and violet. The photon can be absorbed by an atom or molecule. The energy then is used to excite an electron. If the energy is large enough, the electron can be stripped from the atom.

Now I like to tell my physics students that chemistry is the science of electrons. When chemical bonds are rearranged or broken in a chemical reaction, it's the electrons that are being exchanged between the atoms. So when the photon is absorbed, this can cause a chemical reaction - if the energy is large enough.

What colors of light have enough energy and can cause biochemical effects? Roughly speaking, you need ultraviolet light. This is why I wear sunscreen when I golf. What about microwaves? A microwave photon has about 1/100,000 the energy of a UV photon. No chemical reactions here.

You may be wondering about your microwave oven. That certainly cause some chemical reactions, right? Yes, but not through the mechanism described above. In this case, the microwave photon is absorbed by a water molecule, and this makes the water molecule rotate. This added motion translate as added energy to the water making the water hotter.

So can a cell phone cook your brain? No. Through evolution, mammals have a wonderful mechanism for ridding the body of excess heat - the circulatory system. However, we can calculate how much cooking is going on. A typical cell phone emits about 1 Watt of power. In a five minute phone call, this could cause an increase in temperature of 0.1ºC in the brain tissues near your ear.

Yak away. 


A Note Regarding Epidemiology: This is an important field in science-based medicine. Epidemiology aims to find relationships between exposure to agents and mortality (death) and morbidity (disease). The link between cigarette smoking and lung cancer was first found by epidemiologists, long before any understanding of the physical causes.

A good study is difficult. The most serious threat to a good study is bias. Bias comes in three forms: 1. Selection bias in which subjects are taking part because of an unknown factor that happens to be associated with the exposure and the effect. 2. Information bias where the information gathered is flawed. A typical source of information bias example is when subjects are asked to remember information. 3. Confounders are variables that correlate with both the exposure and the effect. For example , a confounder in the power line study may have been the neighborhoods where the subjects lived.