Decreasing the number of balls in the system opens up different states.

(5/6)

So we try to assess the entropy of the states and came up with a neat definition taking into account the degrees of freedom utilized by the system. We evaluate those based on the tracks of translation and rotation in all spheres independently.

(3/6)

It is not as easy as it should be, we thought the same. However, the system undergoes phase transitions and during those the arrow of time becomes evident again.

(2/6)

We have an inherent intuition for the progression of time. In entropy producing systems the arrow of time should appear clear and a reversed movie feels thereby wrong. Look at these macroscopic active spheres and try to figure out whether the movie has been reversed.(1/6)

arxiv.org/abs/2409.16734

And here at last some eye-candy of different polymerization patterns of actin waves.

(12/12)

While uncooperative individuals within the populations destabilize the ordered state or prevent it from arising in the first place - in both systems – preselecting similar individuals renders the ordered state stable even at high densities.

(11/12)

Collectively migrating cells move within a confinement In these populations the nucleation frequencies of the polymerizing actin waves is in synch resulting in a uniform speed.

(10/12)

The nucleation frequency of newly emerging waves of polymerizing actin waves positively correlates with the migration speed of cells.

(9/12)

But is this true for cells? Is the force generating mechanism also synchronized in cells? To address this, we visualized actin polymerization in our cells and the resulting pictures are a feast for the eye.

(8/12)

And by producing balls with transparent half-spheres, we can even see that the synchronization process includes even their driving motors.

(7/12)

To understand the transition between disorder and order, we show that a low number of random selected balls switches between both states. By tracking their shells, we find that their oscillating angular velocity synchronizes.

(6/12)

Visually, the occurring collective motion is strikingly similar to the rotational motion of cells.

(5/12)

On sufficiently rough substrate, the balls roll around with oscillating speed on unstable trajectories. We got a lot of them and put them together... Wait and see what happens!

(4/12)

But how do they self-organize? To understand the process better, we came up with a “toy” model of motorized balls – these active spheres driven by an unbalanced motor freely rotating within a spherical shell.

(3/12)

When I started this project I was mesmerized that monolayers of endothelial cells transition from a disordered motion to a collective rotational state in micron-sized confinement.

(2/12)

Moving some content to this platform.

"Synchronization in collectively moving inanimate and living active matter" - Combining cell biology with an unconventional toy model, we show that synchronization unifies speeds in a collective. rdcu.be/dl0JF

Here is the story: (1/12)

Polymerizing actin creates fireworks that are a sight to behold. This excitable medium produces polymerizing waves similar to those observed in other context. The parallels I tried to lay out in this perspective piece last year: tinyurl.com/53cbxm4v
(LifeAct-GFP in Endothelial Cell)