Time Machine

what is velocity? Velocity is a  vector  expression of the  displacement  that an object or particle undergoes with respect to  time  . The standard unit of velocity magnitude (also known as  speed  ) is the  meter per second  (m/s). Alternatively, the centimeter per second (cm/s) can be used to express velocity magnitude. The direction of a velocity vector can be expressed in various ways, depending on the number of dimensions involved. Velocity is relative. Consider a car moving at 20 m/s with respect to the surface of a highway, traveling northward. If you are driving the car, the velocity of the car relative to your body is zero. If you stand by the side of the road, the velocity of the car relative to you is 20 m/s northward. If you are driving a car at 15 m/s with respect to the road and are traveling northward, and another car moving 20 m/s with respect to the road passes you in the same direction, that other car's velocity...

What is physics? The dictionary definition of physics is “the study of matter, energy, and the interaction between them”, but what that really means is that physics is about asking fundamental questions and trying to answer them by observing and experimenting. Physicists ask really big questions like: How did the universe begin? How will the universe change in the future? How does the Sun keep on shining? What are the basic building blocks of matter? If you think these questions are fascinating, then you’ll like physics. What do Physicists do? Many physicists work in ‘pure’ research, trying to find answers to these types of question. The answers they come up with often lead to unexpected technological applications. For example, all of the technology we take for granted today, including games consoles, mobile phones, mp3 players, and DVDs, is based on a theoretical understanding of electrons that was developed around the turn of the 20th century. Physics doesn’...

Science is . . . Observing the world. Watching and listening Observing and recording. Science is  curiosity in thoughtful action about the world and how it behaves. Anyone can have an idea about how nature works. Some people think their idea is correct because "it seems right" or "it makes sense." But for a scientist (who could be you!), this is not enough. A scientist will test the idea in the real world. An idea that predicts how the world works is called a  hypothesis . "Scientific method"  usually means a  series of steps that scientists follow to discover how nature works. If an idea, or hypothesis, correctly predicts how something will behave, we call it a  theory . If an idea explains all the facts, or evidence, that we have found, we also call it a  theory . These steps will work fine for a school science fair project. But this is not usually the way science actually happens! From observation to theory Sometimes the observ...

Definition of Time Time is something we deal with every day, and something that everyone thinks they understand. However, a  compact and robust definition  of time has proved to be remarkably tricky and elusive. Short Definitions Among the many  short, snappy definitions  of time that have been put forward are: what clocks measure (attr. to physicists Albert Einstein, Donald Ivey, and others) what prevents everything from happening at once (physicist John Wheeler and others) a linear continuum of instants (philosopher Adolf Grünbaum) a certain period during which something is done (Medical Dictionary) a continuum that lacks spatial dimensions (Encyclopaedia Britannica) Although each of these definitions is fine as far as it goes, none of them feel wholly satisfactory. Dictionary Definitions Various  dictionaries  have defined time as follows: the indefinite continued progress of existence and events in the past, present and future r...

Can we travel at the speed of light? The person traveling at the speed of light would experience a slowing of time. For that person, time would move slower than for someone who is not moving. Also, their field of vision would change drastically. The world would appear through a tunnel-shaped window in front of the aircraft in which they are traveling. Speed is thrilling to human beings – there’s no denying. This has been the case ever since the wheel was invented and speed was no longer determined by the strength of our legs. The faster one goes, the more thrilled one feels, although for some, speed can be really intimidating. In today’s modern age, we’ve developed some really fast objects. We have incredibly fast planes, ultra-fast fighter jets, super-fast bullet trains and so on. Still, there is one thing in the universe that is faster than anything we can conceive: Light. Perhaps some of you haven’t thought about this, but many surely have…What wo...

Speed of light The first known discourse on the speed of light comes from the ancient Greek philosopher Aristotle, who penned his disagreement with another Greek scientist, Empedocles. Empedocles argued that because light moved, it must take time to travel. Aristotle, believing light to travel instantaneously, disagreed. In 1667, the Italian astronomer  Galileo  stood two people on a hill at a distance of less than a mile, each holding a shielded lantern. One uncovered his lantern; when the second saw the flash, he uncovered his, as well. By observing how long it took for the light to be seen by the first lantern-holder (and factoring out reaction times), he thought he could calculate the speed of light. Unfortunately, Galileo's distances were too small to see a difference, so he could only determine that light traveled at least ten times faster than sound. In the 1670s, Danish astronomer Ole Römer used eclipses of  Jupiter 's moon, Io, as a chronometer for t...

A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. Because no light can get out, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars. How Big Are Black Holes? Black holes can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Mass is the amount of matter, or "stuff," in an object. Another kind of black hole is called "stellar." Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth's galaxy. Earth's galaxy is called the Milky Way. The largest black holes a...