# Ask-a-Physicist by Topic

## Space & the Universe In general relativity, gravity is described as a distortion of space time. Most vulgarized books use the simplified image of a 2D plane being bent downwards by a mass, so that any matter traveling in the area would have to follow the bending of the plane, which would then explain why things are attracted to one another.

Keeping the same simplified metaphor, could we imagine something that would bend the plane upwards, thus causing objects to be repelled? Would such a thing be considered to have negative mass? Is the concept theoretically possible?

Find out the answer » It looks like they are looking for positive mass particles at the LHC at CERN. Isn't it logical that there are negative-mass "anti-particles"? Does the LHC have the capability of measuring negative mass?

Find out the answer » If a person stepped on a home bathroom scale, and weighed 170 lbs, he would weigh a different weight on this same scale when on other planets due to the force of gravity.

If, however, a person stepped on a professional medical scale — the kind with weights attached that you slide (as opposed to a bathroom scale) and weighed 170 pounds on Earth, would the weight of the person be the same on the other planets as it is on Earth (170 lbs)? This has become a bone of contention in an otherwise ideal marriage.

Find out the answer » Is there a particular range of frequencies at which parts of the human body (or the human body overall) normally vibrates? Because in an episode of the sci-fi TV series Fringe, they claimed that they could figure out if one character was from this universe or a parallel universe by measuring the frequency at which he was vibrating.

Find out the answer » With the latest telescopes, we can look at some galaxy's some 13 billion light years away, correct?

And that is much older than the earth is thought to be. I also heard that we have seen what the universe looked like only a short time from its birth. So how can all this be true? If nothing can travel faster than light and the light from that moment in time would have passed the spot the earths current location long ago, how can we see that light? What am I missing? I can not fathom how we beat the light from the early universe to this spot. Something doesn't add up for me, so can someone break it down for me?

Find out the answer » I've read that orbiting objects like the space station stay in orbit because they are falling at the same rate the Earth is curving away underneath them.

What I don’t understand is their downward velocity should be increasing because it is caused by gravity / acceleration due to gravity. Shouldn’t it be “falling” with a greater velocity the longer it travels? Does it reach a terminal velocity like that of a skydiver? If so Why?

Find out the answer » Under acceleration, a helium-filled balloon inside of a car will jump forward in the direction of acceleration. I have been searching for the reason why with no definitive results. This is the dilemma: An acquaintance of mine, who has a degree from Johns Hopkins is attempting to argue for some magical force that drives the balloon forward, also that it has something to do with gravity.

Find out the answer » My 7 year old son Ben (who is sitting next to me now) has recently become interested in how small things can be. He is not convinced that nothing can be measurably smaller than a Planck length because whatever is Planck sized can always be divided into something smaller.

He thinks perhaps Planck lengths can be divided into energy beams that then become infinite.

Find out the answer » Does Einstein's relativity of simultaneity mean that two events cannot be simultaneous or that we cannot prove that two events occurred simultaneously?

Find out the answer » Assume two photons are moving in opposite directions from each other from a common light source. How fast would they be traveling relative to each other? Twice the speed of light? If the speed of light is the ultimate speed limit in the universe, how can something travel twice that speed?

Find out the answer » Prof. Brian Cox recently stated that the universe is 100 billion light years in diameter. Since the universe is no more than 14 billion years old and nothing exceeds the speed of light, shouldn't it be about 28 billion light years in diameter, not 100?
Find out the answer » How was the universe created if physics states matter can neither be created nor destroyed?
Find out the answer » If you shake the sun, how long would it take before it had an effect on the position of the earth?

Find out the answer » Why does a stationary body above the surface of the earth not change its position after some time while the earth is moving? Suppose if we place an object above the surface of the earth, would it be at the same position after some time and why?
Find out the answer » Question: I want to ask why water is shaped like a ball when it is in space without gravity?
Find out the answer » Would a vertical pipe 50 miles long, one end at or near sea level and the other end in space, suck air into space? It seems as though the vacuum of space should create a flow through the pipe since the pressure at each end is different. - P
Find out the answer » On earth, two objects of different masses fall at the same rate. However, in space, larger masses exert greater gravitational attraction than smaller masses. This seems inconsistent. What am I confusing? - DD, Miami, FL
Find out the answer » Why are the earth and other large celestial objects always spherical? – SP, Mumbai, India
Find out the answer » In his book "Understanding Physics," Isaac Asimov writes "As the earth rotates about its axis, the surface of the earth is continually undergoing an acceleration inward toward the center of the earth (just as the moon does in revolving around the earth." Does that mean that the acceleration on the surface (g = 9.8 m/s2) is directly related to the centripetal acceleration of an object traveling in a circle (a = v2/r)? - DW, Raleigh, NC
Find out the answer » How do I explain the difference between the following two situations to my junior high son: (1) The horizontal velocity of a bullet fired horizontally from a gun has no effect on how long the bullet takes to hit the earth, i.e., how long it takes gravity to bring the bullet down to earth. (2) The horizontal velocity of the Space Shuttle orbiting the earth does affect how long it takes for the Space Shuttle to hit the earth. The velocity of the Space Shuttle makes it keep missing the earth in its free fall. – MMH, Ohio
Find out the answer » Why do we see only one side of the moon and the other side is permanently hidden? - KS, Vienna, Austria
Find out the answer »