Planck length Definition and 81 Threads

This comes from Alex Vilenskin's Many Worlds in One: I didn't think there was such a distance below the Planck length.

Planck length and Planck time are constants, correct? If spacetime changes for an observer who accelerates to subluminal velocities, what happens to these units? If they're constant I'm guessing they can't be "stretched" or "squashed". So do they change in number for a given measurement (say...

Hello everyone. After reading most of the existing topics on the Planck length, I still haven't found what the Planck length really is. Some references say nothing can possibly be smaller than the Planck length, whereas others say it's just a threshold below which "special" things happen...

If there is an irrational solution to an equation for where a particle should be, for example from an ODE, then what effect does Planck length have on that? Does the actual position of the particle get rounded to an a multiple of the Planck length? If it does, wouldn't that imply there is a loss...

Here is a study in distances based on powers of ten of the meter. It gives easy-to-see graphic examples of relative size, from the Plank length out to the Observable Universe. Imho, a great teaching aid. http://www.newgrounds.com/portal/view/589217

How is it possible that 'quantum grains' are many orders of magnitude smaller than 'strings' or the 'Planck length'?

Initially known theories: 1. General consensus: Planck length is smallest measurable unit of length 2. Objects approacing light speed contract in length Scenario: Some hypothetical mass measured to be a Planck length is accelerated infinitely close to light speed. Questions: Can a...

It is generally accepted that a star of sufficient mass collapsing in on itself will form a black hole (singularity) where density is infinite. I see a few problems arising with this, and I would like to have them clarified. 1.) Density=mass/area If the mass of any star is finite, how can an...

Planck length -- Greene versus classics Brian Greene, in Chapter 10 of "The Elegant Universe", offers a sketch of string theory's version of why massive particles have a minimum size of the Planck length. I give my summary of the argument in the next paragraph, and the question in the following...

I've heard of Stephen Hawking talking about the Planck Length and how nothing could exist at a level smaller than that length. I'd like to know how we know this to be certain. It seems that history has always repeated itself in that when humans see as far as we possibly see we simply just...

Can an extra dimension of empty space be smaller than a Planck length? Is that why string theory allows those extra dimensions to be smaller than a Planck length? Because they are empty? I remember reading posters on these forums say that space itself can expand faster than the speed...

How can the Planck length and the speed of light both be universal constants? Will the Planck length change depending on your frame of reference? :)

"The Planck length is the scale at which classical ideas about gravity and space-time cease to be valid, and quantum effects dominate. This is the ‘quantum of length’, the smallest measurement of length with any meaning." What I am wondering about this description is the word "dominate"...

It seems like if you accelerated a massive particle to a high enough velocity (momentum), you could get it's wavelength to be less than the Planck Length. Does that make sense? As always, thanks in advance.

There seems to be a difference in the way relativity views Planck length as frame dependent and the cosmological constant, an energy density?, as invariant...Any insights appreciated! There is a well known contradiction between relativity and the Planck length: Wikipedia explains the...

does anyone know something about the ratio of Planck length to Planck mass : signification, use in quantum relationships...

Homework Statement a. The first part of this problem was to derive the escape speed (Vesc) for a star of mass M and radius R. b. The second part is where I am having trouble. It says to equate the Vesc calculated above and derive a formula for Planck length in terms of c, G, and h_bar...

What happens to the Planck length due to the expansion? Does it grow with the scale factor?

Many arxiv papers state that the Planck length is the smallest measureable length. On the other hand, the gravitational length L=2Gm/c^2 associated with every electron or proton is 19 or 22 orders of magnitude smaller than the Planck length. Nobody seems to doubt either of the two statements...

On a ruler, you could move from the 1cm marking on a ruler to the 2cm marking, or you could move from the 0.5cm marking to the 1.5cm marking - both are 1cm movements but you cannot go from 1.5cm to 1cm in a 1cm movement. If we had Planck co-ordinates, could you move from 1 => 2 and also 1.5 =>...

How are the Planck length, Planck time, and Planck mass "derived"? I know their values, but I don't understand where we get them from.

In "Black Holes, Information and the String Theory Revolution" by Leonard Susskind and James Lindesay, the authors give, (Ch. 15: Entropy of Strings and Black Holes, pg. 170): "The string and Planck length scales are related by g^2* (l_s)^D-2 = (l_p)^D-2 (15.0.23) " They then find...

In "Black Holes, Information and the String Theory Revolution" by Leonard Susskind and James Lindesay, the authors give, (Ch. 15: Entropy of Strings and Black Holes, pg. 170): "The string and Planck length scales are related by g^2* (l_s)^D-2 = (l_p)^D-2 (15.0.23) " They then find...

If you have a object that is about 10^36 less massive than the Earth (about 10^-12 kg) and say it exerts a force on the Earth about 10^-11 Newtons, this would cause the Earth to accelerate about 10^-36 m/s^2. If this object was away from earth, and say if these objects were initial stationary...

Is it appropriate, if I defined Planck Length as the smallest distance possible for a matter to travel?

I know the concept of half a Planck length is wrong. But could someone explain exactly why it is wrong. Also could someone tell me what we conclude about the photon that has moved at C in a Planck time (for example) Do we conclude that the photon was at A and is now at B after the passing of a...

Can someone explain what are they: For egs. What is Planck time, PLanck length, Planck particle etc.

Ok so I understand how we derive Planck Length using the natural constants G,h, and c. However, how do we know this indeed represents the smallest possible length an object in the universe? Or does Planck length just represent the smallest possible length under which gravity is still influential?

Is the Planck length a commonly accepted theory or is it controversial in any way?

Can anyone please shed some light on how the Planck length or Planck time were found? I understand why they have to exist, but what predicts their values? Is it even a prediction or can we actually calculate the Plank length with experiment? Thanks,