Nature Definition and 712 Threads

I understand the forces of gravity, how to model it ect. I even vaguely understand relativistic gravity, but these are just descriptions of how gravity works. What is gravity? Why does mass attract other mass (or warp space time)? Is there an answer for this?

I guess the question is: Is the often used spherical symmetry of the universe just an assumption or is there evidence to support this? I don't mean, nature of 'observing' so much has the properties or symmetry? Trying for an example: many particles have spin -- does the universe have...

Hi, There is definitely overload if you try to look this up online, and you have to pay attention to the dates the sites were made, so I thought I would ask here: What is the latest thinking as to the nature of the universe. Infinite? Finite? Bounded? Unbounded? I am still a...

Neutrons bind Protons in nuclei, and/or the other way around, but why don't Neutrons bind Neutrons, with clumps of neutrons whizzing about? And, I'm guessing this is related: Why is a Neutron unstable outside its nucleus with about a 10.3 minute half-life?

What is flame? What is fire? A form of energy? Or maybe matter?... Anyone here knows the substance of a flame? If it has. I don't know but I am sure I would like to know!

Could someone please explain how science reconciles these statements (both of which I have found in textbooks): *Friction is known as a "contact force" that relies on contact between surfaces for frictional forces to act. *In quantum mechanics, surfaces cannot be in "contact" with one...

Here's a question I've thought about on several occasions: How many levels of derivatives (rates of change) typically occur for objects in nature? For instance, a car has a position, velocity (1st derivative), and acceleration (2nd derivative), but it can also be said to have a rate of...

Can anybody explain why the theory describing quantum gravity is expected to be discrete (rather than a continuum theory), nonlocal (rather than a local theory) and Lorentz violating (rather that a Lorentz invariant theory)?

does the effect of gravitational force vary with state of matter,i.e the force is most felt in gases?right. anything having mass experiences gravity,so 2 gases having masses should experience gravity between themselves.

I have been thinking about the nature of chaos recently and thought of a different way of looking at it. What if "chaos" is really an example of information loss? My rational goes something like this: *classical physics as well as "common sense" suggests that the universe is run by a set of...

Is it correct that Pu cannot be found in nature? What I mean acctually is that while Uranium can be mined, Pu from what I have searchd on wikipedia cannot be mined. I know that Pu is produced in nuclear reactors(or other facilities) from Uranium.

Hi, I have been thinking about the philosophical implications of time and have in the process been analyzing the consequences of time as conceived of by special relativity. I have a couple of questions though, and I would really appreciate it if someone could offer their knowledge in an...

Homework Statement A wagon carries a child. Together mass is 28.5kg. You pull on the handle of the wagon at an angle of 40degrees from the horizontal. The wagon travels over a level horizontal sidewalk. A force of friction of 12.0N acts on the wagon. a) What is the net force acting on the...

Homework Statement A crate of mass 50.0 kg is pulled across a level concrete floor by a force of 300.0 N acting 30.0 degrees above the horizontal. The crate moves at a constant velocity of 0.962 m/s. What is the force of friction acting on the crate? Homework Equations SINE, COSINE...

For the composite system of identical particles only symmetric and antisymmetric states in the tensor-product (from the one-particle spaces) space are allowed to represent particles in nature. Why is that? Is it an experimental fact which is used as an input in the theory of many particle QM...

What is human nature and what is known by human instincts? What's the difference between the two? Is there any distinct line differentiating the two?

Hi, I was wondering what really ARE spectral lines? Are they electromagnetic waves? But still they are affected by magnetic & electric field in the Zeeman and Starks effect respectively, whereas the electromagnetic waves are not. so is there any theory explaining...

Do you think time flows or is static? Is time continuous or quantized? Is the direction of time uniquely defined and irreversible? Is time just a figment of our imagination? FQXI has an essay contest about the nature of time. All these points of view are championed by various authors...

I will start by saying I am not a physicist and what I am posting here is pure thought experiment on my part. I was wondering about the nature of gravity, and trying to determine how the force could act to pull two objects together. What physical interaction causes two objects to accelerate...

This video is worth watching. http://pirsa.org/08120001/ Quantum Nature of the Big bang in Simple Models. Abhay Ashtekar Perimeter video with slides PDF 3 December 2008 "According to general relativity, space-time ends at singularities and classical physics just stops. In particular, the big...

Homework Statement The equation of a curve is y=\frac{3x}{\sqrt{1+x}}. Given that the equation of the tangent to the curve at the point x=3 us 15x-16y=k , find the value of k. [SIZE="5"]SOLVED Homework Equations The Attempt at a Solution

Homework Statement This is from Advanced Physics by Adams and Allday, section 8, practice exam questions, question 25. An α-source with an activity of 150 kBq is placed in a metal can. A 100 V d.c. source and a 109 Ώ resistor are connected in series to the can and the source. This...

Neutrinos are elementary particles that have the ability to pass through any matter. Billions of them pass through our bodies every second. Billions of them pass through the Earth and exit on the other side unaffected. They can pass through stars and travel to the other side of the universe...

Why is the Higgs field a scalar field? I understand if it is one, it will have no spin and no angular momentum. But understanding that a particle is a scalar seems to me a leap of faith. What am I not getting?

I'm trying to make sense of the way time dimension is related to the other 3, the example is twin paradox: Observer 1 is moving away at 0.866c from observer 2, who is standing still, then turns around at a defined point and goes back at the same speed, arriving back to observer 2 position...

Can someone please clear up the nature of length contraction Does the spatial dimension parallel to the motion of a moving metre stick contract (as seen by a stationary observer). Or Is contraction a purelly matter phenomenon whereby space is constant and the actual material of the...

Hi I had some questions about the nature of the spectrum of electromagnetic radiation, as to whether it is continuous or quantifiable, and whether it is infinite or finite. I haven't been able to find satisfactory answers so far and I'm very interested in the knowledge of this forum. Can the...

I have been having trouble with this problem and don't understand why. A shopper pushes a 7.5 kg shopping cart up at a 13 degree incline, find the magnitude of the horizontal force, needed to give the cart an acceleration of 1.41m/s2 The answer is supposed to be 28 N and I don't know how...

FQXi has an essay contest on the Nature of Time. http://fqxi.org/community/forum/category/10" There is an internal commission but the winner depends also on the public vote. Here is possible to vote: http://fqxi.org/community/vote" (vote your favourite one!) and it's very nice that there is...

Homework Statement A convex lens (f1=300mm) is placed 200 mm from a concave lens (f2=-50mm). An object is placed 6m away form the convex lens. (the order is as follows: object - 6m - convex lens - 200mm - concave lens). Determine the position, magnification and nature of a final image...

Science poetry--or verse that is just informative about nature In another thread, Mormonator mentioned poetry about particle physics. This reminds me of John Updike's Neutrino poem and Franck Wilczek's Virtual Particles sonnet. And Borges sonnet about 4D spacetime. Maybe we should try...

If anyone of you know a thing or two about spirits if they are affected by forces of nature like gravity, wind, matter, etc. Not that you have witnessed or experienced beforehand but maybe you possesses 2nd hand knowledge regarding this matter. Also not that they are real, I just want info...

Can anyone inform me?

To grasp basic physics I need an idea of the nature of the particles which comprise its object. When I search beyond "a big positive thing and a little negative thing", I find lots of attempts to view and destroy but no simple explanation of what is being watched or pulverized. I read of...

Don't "mechanical advantage" disagree with the law of nature ? hello I just can't swallow the idea of mechanical advantage. * if you have a 10 KG mass , you need , say , 100 N to left it up * if your friend helps you , each one of you will exert only 50 N * but if you are alone , and...

Why is the standard form of a linear equation ax + by = c? What is the significance of this particular way of writing the equation that makes it "standard"? When we graph a line, we always transform the equation into something else, such as the point-slope form, y = mx + b. In other words...

Please, I need a list of definitive experiments that revealed light's nature.

There is a EM radiation of frequency suppose x Hz.Let it has to travel a distance of y m.Now what's the time required for the radiation to travel the distance?The question seems to be very easy, but my confusion is in how can the frequency,distance,speed and time can be related? Can someone give...

Can anyone tell me, what is so important about prime numbers in science?

One commonly hears that Quantum Mechanics refutes or disproves the principle of causality. and yet if this were the case, qm could not be used to build highly precise machines such as lasers. the truth is that qm makes of use of a modified causality. the normal causal relation is that...

Hi, I was just wondering about the nature of fields. What are they? Since fields carry energy, and energy is mass, does that mean that fields are equivalent to mass?? I think this is probably incorrect, but I just have no clue why.

I know I am probably missing the point, but something is not clicking for me in understanding time as a dimension. Isn't time just an arbitrary measurement of distance? It's always just us 'counting hippopotamuses' while watching something moving from point A to point B (we don't have to...

Homework Statement "Explain the statement that one's eyes could not detect the faint star-light if light were not particle like" Homework Equations The Attempt at a Solution What comes to my mind is that when light from outside enters the atmosphere,it gets refracted...referred to...

‘The genius of man may make various inventions, encompassing with various instruments one and the same end; but it will never discover a more beautiful, a more economical, or a more direct one than nature’s, since in her inventions nothing is wanting and nothing is superfluous’ - Leonardo da...

if the Plasma membrane is amphipathic (hydrophobic and hydrophilic), why does it only allow hydrophobic stuff to pass thru?

We are discussing the Demystifier's paper "Quantum mechanics: myths and facts". http://xxx.lanl.gov/abs/quant-ph/0609163 Previously: Myth 1 https://www.physicsforums.com/showthread.php?t=229497 Myth 2 https://www.physicsforums.com/showthread.php?t=230693 QM implies that nature is...

The hunt for superheavy elements has focused banging various heavy nuclei together and hoping they’ll stick. In this way, physicists have extended the periodic table by manufacturing elements 111, 112, 114, 116 and 118, albeit for vanishingly small instants. Although none of these elements is...

Homework Statement (a) What is the minimum energy (in electron volts) that is required to remove the electron from the ground state of an ionized atom (Z=2)? (b) What is the ionization energy for this ion? Homework Equations After doing what I got the answer for part (b)... but I don't...

Are we no more than animals, I know we separate our selves from the animals because we can manipulate our environment, shape and mold things out of steal. I think we are a truly violent race; if you would put 30 people in a room with no way out, the people would divide themselves and invertible...

Flattening of a planet Hi all, Does anyone know how to calculate the flattening of a planet, say a gaseous one for simplicity, simply from it's radius and rotational period? Natski