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1500 questions
60
votes
6 answers
Can a Skydiver Land On a Large Slide and Survive?
Please forgive my lack of artistic ability, but here's my question:
Consider that a skydiver, without using his parachute, were to fall exactly parallel to a giant curved slide that starts at $90\,^\circ$ perpendicular to the ground and gradually…
MegaMark
- 706
60
votes
2 answers
What can the D-Wave quantum computer do?
The media are reporting the commercially sold 128-bit quantum computer from D-Wave
http://news.google.com/news?ned=us&hl=us&q=d-wave+quantum&cf=all&scoring=n
which of course sounds amazing. The gadget is described as something capable of doing…
Luboš Motl
- 179,018
59
votes
5 answers
Fundamental question about dimensional analysis
In dimensional analysis, it does not make sense to, for instance, add together two numbers with different units together. Nor does it make sense to exponentiate two numbers with different units (or for that matter, with units at all) together; these…
Jubilee
- 593
59
votes
5 answers
Do two beams of light attract each other in general theory of relativity?
In general relativity, light is subject to gravitational pull. Does light generate gravitational pull, and do two beams of light attract each other?
Jakub Narębski
- 925
59
votes
9 answers
How do different definitions of entropy connect with each other?
In many places over the Internet, I have tried to understand entropy.
Many definitions are presented, among which I can formulate three (please correct me if any definition is wrong):
Entropy = disorder, and systems tend to the most possible…
Saeed Neamati
- 1,127
59
votes
7 answers
Is the weight of the aircraft flying in the sky transferred to the ground?
Is the weight of the aircraft flying in the sky transferred to the ground? Is the weight of people swimming in the pool also transferred to the ground? How can we prove it?
enbin
- 1,972
59
votes
11 answers
Is spacetime wholly a mathematical construct and not a real thing?
Speaking of what I understood, spacetime is three dimensions of space and one of time. Now, if we look at general relativity, spacetime is generally reckoned as a 'fabric'. So my question is, whether spacetime is real or is just a mathematical…
OmG
- 639
59
votes
6 answers
Haag's theorem and practical QFT computations
There exists this famous Haag's theorem which basically states that the interaction picture in QFT cannot exist. Yet, everyone uses it to calculate almost everything in QFT and it works beautifully.
Why? More specifically to particle physics: In…
Rafael
- 2,731
59
votes
7 answers
Could a human beat light in a footrace?
Is there anything preventing the following experiment from being done right now?
Imagine that a human ran from point 'a' to point 'b' while light
particles that reflected off a clock moved through a special medium
from point 'a' to point 'b' as…
Josh
- 1,315
59
votes
6 answers
What is the connection between special and general relativity?
What is the connection between special and general relativity? As I understand general relativity does not need the assumption on speed of light constant.
It is about the relation between mass and spacetime and gravity.
Can general relativity be…
Sharon Salmon
- 709
59
votes
8 answers
Is it possible to send all nuclear waste on Earth to the Sun?
If we neglect the danger of unsuccessful lift-off of the rocket and the cost, would it be physically possible to send all nuclear waste on Earth to the Sun?
Will there be an obstacle that prevents this? For example, solar winds?
Mubin Icyer
- 679
59
votes
3 answers
Why is boiling water loud, then quiet?
Water in my electric kettle makes the most noise sixty to ninety seconds before the water comes to a full boil. I have been fooled many times by the noisy kettle, only to discover that the water was not yet hot enough for tea. The kettle is only at…
Mark Dominus
- 2,688
59
votes
4 answers
How does gravity work underground?
Would the effect of gravity on me change if I were to dig a very deep hole and stand in it? If so, how would it change? Am I more likely to be pulled downwards, or pulled towards the edges of the hole? If there would be no change, why not?
Mia Clarke
- 693
59
votes
4 answers
Does time move slower at the equator?
While answering the question GPS Satellite - Special Relativity it occurred to me that time would run more slowly at the equator than at the North Pole, because the surface of the Earth is moving at about 464 m/s compared to the North Pole. The…
John Rennie
- 355,118
59
votes
8 answers
Will a blanket warm you if you are underwater?
Suppose a man falls into very cold water and gets their foot stuck under a heavy rock. Fortunately, his head is above water and someone is able to call for help. The paramedics want to keep him warm while they work on freeing his foot. They put a…
Moby Disk
- 698