## The Big Bang Theory of the Inclined Plane

Season 01, Episode 02: “The Big Bran Hypothesis”

Sheldon and Leonard contemplate using the stairs as an inclined plane to move Penny’s furniture to her apartment.

In Season 1 Episode 2 of The Big Bang Theory, “The Big Bran Hypothesis”, Penny (Kaley Cuoco) asks Leonard (Johnny Galecki) to sign for a furniture delivery if she isn’t home. Unfortunately for Leonard and Sheldon, they are left with the task of getting a huge (and heavy) box up to Penny’s apartment.

To solve this problem, Leonard suggest using the stairs as an inclined plane, one of the six classical simple machines defined by Renaissance scientists. Both Leonard and Sheldon have the right idea here. Not only are inclined planes used to raise heavy loads but they require less effort to do so. Though this may make moving a heavy load easier the tradeoff is that the load must now be moved over a greater distance. So while, as Leonard correctly calculates, the effort required to move Penny’s furniture is reduced by half, the distance he and Sheldon must move Penny’s furniture twice the distance to raise it directly.

# Mathematics of the Inclined Plane

## Effort to lift block on Inclined Plane

Now we got an inclined plane. Force required to lift is reduced by the sine of the angle of the stairs… call it 30 degrees, so about half.

Free-body Diagram of a block on an inclined plane. It shows the forces acting on a block and the force needed to keep it stationary and not let it slip down.

To analyze the forces acting on a body, physicists and engineers use rough sketches or free body diagrams. This diagram can help physicists model a problem on paper and to determine how forces act on an object. We can resolve the forces to see the effort needed to move the block up the stairs.

If the weight of Penny’s furniture is $$W$$ and the angle of the stairs is $$\theta$$ then
$\angle_{\mathrm{stairs}}\equiv\theta \approx 30^\circ$
and
$\Rightarrow\sin 30^\circ = \frac{1}{2}$
So the effort needed to keep the box in place is about half the weight of the furniture box or $$\frac{1}{2}W$$, just as Leonard says.

## Distance moved along Inclined Plane

The relationship between the height $$h$$ the block is raised and the distance it moves $$d$$ is the sine of the angle $$\theta$$.

While the inclined plane allows Leonard and Sheldon to push the box with less effort, the tradeoff is that the distance they move along the incline is twice the height to raise the box vertically. Geometry shows us that
$\sin \theta = \frac{h}{d}$
We again assume that the angle of the stairs is approximately $$30^\circ$$ and $$\sin 30^{\circ} = 1/2$$ then we have $$d=2h$$.

# Uses of the Inclined Plane

We see inclined planes daily without realizing it. They are used as loading ramps to load and unload goods. Wheelchair ramps also allow wheelchair users, as well as users of strollers and carts, to access buildings easily. Roads sometimes have inclined planes to form a gradual slope to allow vehicles to move over hills without losing traction. Inclined planes have also played an important part in history and were used to build the Egyptian pyramids and possibly used to move the heavy stones to build Stonehenge.

## Lombard Street (San Francisco)

Lombard Street is one of the most visited street in San Francisco as seen from Coit Tower. It is best known for the one-way section on Russian Hill between Hyde and Leavenworth Streets, in which the roadway has eight sharp turns (or switchbacks) that have earned the street the distinction of being the crookedest “most winding “street in the world, though this title is contested. (Photo by David Yu).

Lombard Street in San Francisco is famous for its eight tight hairpin turns (or switchbacks) that have earned it the distinction of being the crookedest street in the world (though this title is contested). These eight switchbacks are crucial to the street’s design as the reduce the hills natural 27° grade which is too steep for most vehicles. It is also a hazard to pedestrians, who are more accustomed to a more reasonable 4.86° incline due to wheel chair navigability concerns.

Technically speaking, the “zigzag” path doesn’t make climbing or coming down the hill any easier. As we have seen, all it does is change how various forces are applied. It just requires less effort to move up or down but the tradeoff is that you travel a longer distance. This has several advantages. Car engines have to be less powerful to climb the hill and in the case of descent, less force needs to be applied on the brakes. There are also safety considerations. A car will not accelerate down the switch back path as fast than if it was driven straight down, making speeds safer and more manageable for motorists.

This idea of using zigzagging paths to climb steep hills and mountains is also used by hikers and rock climbers for very much the same reason Lombard Street zigszags. The tradeoff is that the distance traveled along the path is greater than if a climber goes straight up.

# The Descendants of Archimedes

We don’t need strength, we’re physicists. We are the intellectual descendants of Archimedes. Give me a fulcrum and a lever and I can move the Earth. It’s just a matter of… I don’t have this, I don’t have this!

We see that Leonard had the right idea. If we were to assume are to assume — based on the size of the box — that the furniture is approximately 150 lbs (65kg) and the effort is reduced by half, then they need to push with at least 75 lbs of force. This is equivalent to moving a 34kg mass. If they both push equally, they are each left pushing a very manageable 37.5 lbs, the equivalent of pushing a 17kg mass.

Penny’s apartment is on the fourth floor and we if we assume a standard US building design of ten feet per floor, this means a 30 foot vertical rise. The boys are left with the choice of lifting 150 lbs vertically 30 feet or moving 75lbs a distance of 60 feet. The latter is more manageable but then again, neither of our heroes have any upper body strength.

## The Big Bang Theory of Trans-Neptunian objects

Season 02, Episode 04: “The Griffin Equivalency”

Rajesh Koothrappali (Kunal Nayyar) looks pleased as he talks about his inclusion into People magazine’s “30 Under 30 to watch” list for his discovery of the fictional trans-Neptunian object, 2008 NQ17 which exists beyond the Kuiper belt

In “The Griffin Equivalency” episode of The Big Bang Theory, Raj (Kunal Nayyar) announces that he has been chosen as one of People Magazine’s “30 visionaries under 30 years to watch” list for his discovery of the trans-Neptunian object 2008 NQ17. This fictional astronomical body exists just beyond the Kuiper Belt, a region of the Solar System that extends from the orbit of Neptune (about 30 Astronomical units(AU) away), to a distance of 50AU from the Sun. (1AU is roughly the distance of the Earth from the Sun).

The distribution and classification of the trans-Neptunian Objects in our solar system

The first trans-Neptunian object discovered was Pluto in 1930 and is the second most massive known dwarf planet in the Solar System. These objects are so small and distant that it wasn’t until 1992 that the second trans-Neptunian object orbiting the Sun, (15760) 1992 QB1, was discovered. As cryptic as these names sound, i.e 2008 NQ17 and 1992 QB1, the nomenclature comes from a provisional designation in astronomy that names objects immediately following their discovery. Once a proper orbit has been calculated, a permanent designation consisting of a number-name combination is given by the Minor Planet Center. Unfortunately for Raj, so many of these minor planets are discovered that most won’t be named for their discoverers.

# Provisional designation of Minor Planets

The provisional naming system for minor planets, of which dwarf planets, asteroids, trojans, centaurs, Kuiper belt objects, and other trans-Neptunian objects are a part of, have been in place since 1925. The first element in a minor planet’s provisional designation is the year of discovery, followed by two letters and sometimes a number.

The first letter indicates the “half-month” of the object’s discovery. “A” denotes a discovery in the first half of January (between January 1st and January 15th) while “B” denotes a discovery in the second half of January (between January 16th and January 31st). The letter “I” is not used so the letters go all the way up to “Y”. The first half is always the 1st through to the 15th of the month, regardless of the numbers of days in the second “half”.

First Letter (A-G)
A B C D E F G
Jan 1 Jan 16 Feb 1 Feb 16 Mar 1 Mar 16 Apr 1

First Letter (H-O)
H J K L M N O
Apr 16 May 1 May 16 Jun 1 Jun 16 Jul 1 Jul 16

First Letter (P-V)
P Q R S T U V
Aug 1 Aug 16 Sep 1 Sep 16 Oct 1 Oct 16 Nov 1

First Letter (W-Y)
W X Y
Nov 16 Dec 1 Dec 16

The second letter and the number indicate the order or discovery within that half-month.

Second Letter (A-K)
A B C D E F G H J K
1 2 3 4 5 6 7 8 9 10

Second Letter (L-U)
L M N O P Q R S T U
11 12 13 14 15 16 17 18 19 20

Second Letter (V-Z)
V W X Y Z
21 22 23 24 25

So the 14th minor planet discovered in the first half of June 2013 will get the provisional planetary designation 2013 LO. As modern techniques has made it (relatively) easier to detect these objects, there can be more than 25 discoveries in a given half-month. To solve this a subscript number is added to indicate the number of times that the letters have cycled through. So the 40th minor planet to be discovered in the first half of June 2013 will gain the designation 2013 LP1.
\begin{aligned} 40 & = 25 + 15 \\ \therefore P & = 15 \end{aligned}

# Planet Bollywood

Using this information we can calculate when Raj discovered “Planet Bollywood”. It was discovered some time between July 1-15 and it was the 441st minor planet to be discovered in that half month.
\begin{aligned} Q & = 16 \\ 25 \times 17 & = 425 \end{aligned}
And $$425 + 16 = 441$$.

It must have been a particularly busy month in the Big Bang Theory Universe. A quick check at the Minor Planet Center’s Provisional Designations webpage indicates that there were 137 astronomical bodies discovered in that half-month. That would make that last trans-Neptunian object to be discovered to receive the provisional designation 2008 NM4.

Long live Planet Bollywood!

## The Big Bang Theory of the Rolling Ball Problem

Big Bang Theory Season 2, Episode 5: “The Euclid Alternative”

In the opening scene of the “The Euclid Alternative”, we see Sheldon (Jim Parsons) demanding that Leonard (Johnny Galecki)needs to drive him around to run various errands. Leonard, after spending a night in the lab using the new Free Electron Laser to perform X-ray diffraction experiments. In the background, we can see equations that describe a rolling ball problem on the whiteboard in the background.

Scene with Sheldon Cooper. The background shows a whiteboard with the physics equations of a rolling ball.

Rolling motion plays an important role in many familiar situations so this type of motion is paid considerable attention in many introductory mechanics courses in physics and engineering. One of the more challenging aspects to grasp is that rolling (without slipping) is a combination of both translation and rotation where the point of contact is instantaneously at rest.The equations on the white board describe the velocity at the point of contact on the ground, the center of the object and at the top of the object.

# Pure Translational Motion

An object undergoing pure translational motion

When an object undergoes pure translational motion, all of its points move with the same velocity as the center of mass– it moves in the same speed and direction or $$v_{\textrm{cm}}$$.

# Pure Rotational Motion

An object undergoing pure rotational motion. The velocity of each point of the object depends on the distance away from the center. The further away the faster it moves as can be seen by the length of the arrows.

In the case of a rotating body, the speed of any point on the object depends on how far away it is from the axis of rotation; in this case, the center. We know that the body’s speed is $$v_{\textrm{cm}}$$ and that the speed at the edge must be the same. We may think that all these points moving at different speeds poses a problem but we know something else — the object’s angular velocity.
The angular speed tells us how fast an object rotates. In this case, we know that all points along the object’s surface completes a revolution in the same time. In physics, we define this by the equation:

\omega=\frac{v}{r}

where $$\omega$$ is the angular speed. We can use this to rewrite this equation to tell us the speed of any point from the center:

v(r)=\omega r

If we look at the center, where $$r=0$$, we expect the speed to be zero. When we plug zero into the above equation that is exactly what we get:

v(0)= \omega \times 0 = 0
\label{eq:zero}

If we know the object’s speed, $$v_{\textrm{cm}}$$ and the object’s radius, $$R$$, using a little algebra we can define $$\omega$$ as:
$\omega=\frac{v_{\textrm{cm}}}{R}$
or the speed at the edge, $$v_{\textrm{cm}}$$ to be $$v(R)$$ to be:

v_{\textrm{cm}}=v(R) = \omega R
\label{eq:R}

# Putting it all Together

An object that rolls undergoes both translational and rotational motion. To determine the speed at any point we must add both of these speeds. We see the translational speed show in red and the rotational speed show in in blue.

To determine the absolute speed of any point of a rolling object we must add both the translational and rotational speeds together. We see that some of the rotational velocities point in the opposite direction from the translational velocity and must be subtracted. As horrifying as this looks to do, we can reduce the problem somewhat to what we see on the whiteboard. Here we see the boys reduce the problem and look at three key areas, the point of contact with the ground ($$P)$$, the center of the object, ($$C$$) and the top of the object ($$Q$$).

Rendering copy of the whiteboard showing the rolling ball problem as seen on the Big Bang Theory.

We have done most of the legwork at this point and now the rolling ball problem is easier to solve.

## At point $$Q$$

At point $$Q$$, we know the translational speed to be $$v_{\textrm{cm}}$$ and the rotational speed to be $$v(R)$$. So the total speed at that point is

v = v_{\textrm{cm}} + v(R)
\label{eq:Q1}

Looking at equation \eqref{eq:R}, we can write $$v(R)$$ as

v(R) = \omega R

Putting this into \eqref{eq:Q1} and we get,
\begin{aligned}
v & = v_{\textrm{cm}} + v(R) \\
& = v_{\textrm{cm}} + \omega R \\
& = v_{\textrm{cm}} + \frac{v_{\textrm{cm}}}{R}\cdot R \\
& = v_{\textrm{cm}} + v_{\textrm{cm}} = 2v_{\textrm{cm}}
\end{aligned}
which looks almost exactly like Leonard’s board, so we must be doing something right.

## At point $$C$$

At point $$C$$ we know the rotational speed to be zero (see equation \eqref{eq:zero}).
Putting this back into equation \eqref{eq:Q1}, we get
\begin{aligned}
v & = v_{\textrm{cm}} + v(r) \\
& = v_{\textrm{cm}} + v(0) \\
& = v_{\textrm{cm}} + \omega \cdot 0 \\
& = v_{\textrm{cm}} + 0 \\
& = v_{\textrm{cm}}
\end{aligned}
Again we get the same result as the board.

## At point $$P$$

At the point of contact with the ground, $$P$$, we don’t expect a wheel to be moving (unless it skids or slips). If we look at our diagrams, we see that the rotational speed is in the opposite direction to the translational speed and its magnitude is
\begin{aligned}
v(R) & = -\omega R \\
& = -\frac{v_{\textrm{cm}}}{R}\cdot R \\
& = -v_{\textrm{cm}}
\end{aligned}
It is negative because the speed is in the opposite direction. Equation \eqref{eq:Q1}, becomes
\begin{aligned}
v & = v_{\textrm{cm}} + v(r) \\
& = v_{\textrm{cm}} – \omega R \\
& = v_{\textrm{cm}} – \frac{v_{\textrm{cm}}}{R}\cdot R \\
& = v_{\textrm{cm}} – v_{\textrm{cm}} = 0
\end{aligned}
Not only do we get the same result for the rolling ball problem we see on the whiteboard but it is what we expect. When a rolling ball, wheel or object doesn’t slip or skid, the point of contact is stationary.

# Cycloid and the Rolling ball

The path a point on a rolling ball draws is called a cycloid.

If we were to trace the path drawn by a point on the ball we get something known as a cycloid. The rolling ball problem is an interesting one and the reason it is studied is because the body undergoes two types of motion at the same time — pure translation and pure rotation. This means that the point that touches the ground, the contact point, is stationary while the top of the ball moves twice as fast as the center. It seems somewhat counter-intuitive which is why we don’t often think about it but imagine if at the point of contact our car’s tires wasn’t stationary but moved. We’d slip and slide and not go anywhere fast. But that is another problem entirely.

## The Wibbly Wobbly of Continuum

The series Continuum is a time travel science fiction TV show that follows the adventures of City Protective Services (CPS) law enforcement officer Kiera Cameron (Rachel Nichols) as she attempts to stop the self-proclaimed freedom fighters known as “Liber8”. It is easy to dismiss many science fiction shows dealing with time travel for the simple reason so many of them are done badly. Continuum is different in that there is an underlying mystery. A big part of that mystery is the motivation of an older Alec Sadler (William B. Davis) and the principles on which Continuum’s time travel is based.

# The Continuum World of 2077

In 2077, the future of this world is both a distopian and Orwellian. World governments have somehow failed and, by implication, we assume so too has democracy. This has given way to a corporate controlled government that monitors and records every moment of a person’s life. People are born indebted and indentured to  the Global Corporate Congress until they pay off their life debts.

Among the largest corporations in the North American Union and possibly the world is SadTech, owned by Alec Sadler — a genius responsible for inventing and developing much of the technology we see in the world of Continuum. This hasn’t only made Sadler one of the richest men in the world but possibly one of the most powerful.

In an attempt to end the corporation’s rule over the people, Liber8 leader, Edouard Kagame (Tony Amendola) attempts to bring down the Corporate Congress by blowing up the building where a scheduled meeting is to take place thereby killing all 20 members. To Kagame’s surprise Sadler is the sole survivor. Sadler gives Kagame a time travel device to allow Liber8 to escape into the past; Sadler’s full intentions are unknown.

Upon arriving in 2012, Kiera meets and befriends a younger Alec Sadler (Erik Knudsen) who is coming to terms with the loss of his father and has decided to follow his father’s work and research. The beginnings of much of the “tech” that Keira uses was developed by Alec’s father. The young Alec posits two likely time traveling scenarios, both of which have their roots in physics. Evidence for both scenarios has been presented over the course of the first season and they both seem equally valid. The first is a “time loop” where conditions can not be altered. Everything that is happening has already happened and will give way to the future that Kiera knows. The second is an alternate time line and the very presence of both Kiera and Liber8 have altered Continuum’s 2077 future.

## Time Loop

The first possibility is the “time loop” where the older Alec, knowing of his interactions in 2012 with Kiera, deliberately sends her back in time. This fulfills the events in the past and allow the future to progress in the way it has. All the events we see in 2012 have already happened and none of the Continuum characters can deviate from that. In a sense, everything is preordained. One of the most tantalizing clues, though unrelated, clues is the presence of Mr. Escher, the unknown head of the high security government agency, Section 6, who vouches for Kiera to the Vancouver Police Department.

“Ascending and Descending” is a lithograph print by the Dutch artist M. C. Escher which was first printed in March 1960. This perpetual loop illustrates the concept of the time loop used in Continuum.

This name may be a hidden clue that supports the the Time Loop theory. It may  Continuum’s writers way of telling viewers which of the two theories are correct. The name may have been taken from the Dutch artist, Maurits Cornelis Escher or M.C. Escher, who is best known for his mathematically inspired artwork. Escher was known for his depictions of impossible realities, especially those that related to infinite loops in some way. The “Ascending and Descending” litographic print is an artistic depiction of the “Penrose stairs“, an impossible object created by Lionel and Roger Penrose . The reality bending idea of the Penrose Stairs was used in the 2010 movie “Inception”.

The ants crawl along a Möbius strip. This is another illustration of the principle of a time loop in the TV series Continuum.

In addition to impossible objects, Escher’s art also features insects. One of his paintings, Möbius Strip II (Red Ants), shows an ant walking along a surface with only one side — a Möbius strip. This strip looks very much like the infinity symbol. If an ant was to start at one point on the strip it will eventually return to that same point. We can create a Möbius strip of our own by twisting one end of a strip of paper by one half-turn and gluing the ends together. This object was dicovered independently by August Ferdinand Möbius and Johann Benedict Listing in 1858.

If this name is really a clue, then it add credibility to the time loop hypothesis. It could also mean that the reason that the older Sadler sends Keira back into time isn’t just to preserve the future but because he has to; he knows and recalls his interactions with this time traveling cop in his past.

This raises the question, can Kiera or Liber8 do anything to change the future? Does it mean that every little action, from the coffee they drink in the morning to the time they go to bed at night, has already been scripted? Can they do anything that might create a time paradox?

To resolve the problem of time paradoxes, which is permitted in some solutions of Einstein’s Theory of General Relativity, Russian physicist Igor Dmitriyevich Novikov came up with his self-consistency principle . In simplest terms, the Novikov self-consistency principle says that if an event exists that would give rise to a paradox, or to any “change” to the past whatsoever, then the probability of that event is zero. This means that it is impossible to create time paradoxes.

Some may find this idea unpalatable as it interferes with our ideas of free will and destiny. Does it mean that Kiera and Alec and all of Liber8 are doing nothing more than following a script from which they can never deviate? Well, not entirely. The Novikov self-consistency principle does not imply that time traveler have no free-will. It just says that the results of their actions can not produce inconsistent results. Kiera can choose what to have for lunch but not stop the bombing of the building even if she tried. If she succeeded, her actions would be inconsistent with how events unfold in the future.

## Alternate Timelines & the Many Worlds of Continuum

Alec also considers the possibility that Kiera’s and Liber8’s presence may have altered the time line making the fate of 2077 is uncertain. But what does that mean for the inhabitants of 2077 if Liber8 or even Kiera make a change in the present? Do they “blink” out of existence just like old Biff Tannen in Back to the Future II? No, they don’t have to and quantum mechanics may provide an answer.

To resolve some of the strange results observed in quantum mechanics, physicist Hugh Everett came up with his Many-Worlds Interpretation in 1957 . In this version of quantum mechanics, at every single instant of the tiniest portion of a second the Universe is splitting into countless billions of parallel universes. Thus our Universe branches out in which every possibility exists. The arrival of Kiera and Liber8 in the past results in a a new branch and a new alternate reality. This idea was seen in the 2009 Star Trek reboot. This spells bad news for Kiera as she can only travel to the future of the new time-line she is already in. Getting home or to the timeline she came from is an impossibility.

# So which is it?

It’s difficult to say which of the two hypotheses are true as the series has given evidence to support either hypothesis. In “A Test of Time”, Kagame decides to test these theories of time travel. If Liber8 were to kill Kiera’s grandmother, then the threat posed by this future cop would literally cease to exist. While Kiera manages to save her grand-mother, Matthew Kellog’s (a former Liber8 member) teenage grandmother is killed in a confrontation between Kiera and Liber8.

Matthew’s continued existence provides no clear answers as Alec explains at the end of the episode. While we are certain who Kiera’s grandmother was, we are not quite sure in Kellog’s case. For all we know, Kellog could have been mistaken about the young girl’s identity and she was never his grandmother. The young girl could also have been Kellog’s grandmother and though she died thus preventing Matthew’s future birth, Kellog’s journey through time might protect him from this causality paradox. It does mean that the future can be changed which gives Liber8 even more incentive to succeed.

# The good and bad guys in Continuum

If the future is a bad place to live and Kiera is trying to preserve the future, does that mean she is the bad guy? Liber8’s methods and motivations, while they are extreme, are to free the world from a tyrannical and oppressive system from ever taking place. Both sides are fighting to save the future they believe in. Liber8 seeks to create a better world while Kiera is trying to preserve her family’s existence. Neither knows if that is even possible.

It all comes down to one man, the older Alec Sadler and his ultimate goal and motivations. Young Alec discovers at the end of the season finale that he is the reason that Kiera is now living in the past. Did he send Kiera and Liber8 to save the future or to preserve it? Whatever the answer, we are going to have to wait for the answer in future episodes.

## Otto Loewi, the “Father of Neuroscience”

Otto Loewi, Nobel Prize in Physiology or Medicine 1936

June 3, 1873 marks Otto Loewi’s birthday. This German born pharmacologist is known for his discovery of acetylcholine, a neurotransmitter found in both the peripheral and central nervous systems of many organisms including humans. For his discovery, he was awarded the 1936 Nobel Prize in Physiology or Medicine with Sir Henry Dale. Loewi is also known as the “Father of Neuroscience.”

## The problem of Neuron Transmission

Between 1836 and 1838, scientists were first able to describe the first cells in nervous tissue. Gabriel Gustav Valentin (1810-1863) was the first to describe the cell, nucleus and nucleolus of neurons, in 1836. By the time Otto Loewi enters university in 1891, the term neuron is being used the cells in the brain. In 1906, both Santiago Ramón y Cajal and Camillo Golgi are awarded the Nobel Prize in Medicine “in recognition of their work on the structure of the nervous system”. Both men had completely different points of view regarding brain organization with the scientific community divided between the reticularist doctrine and neuronal theory.

Drawing of the cells of the chick cerebellum by Santiago Ramón y Cajal, from “Estructura de los centros nerviosos de las aves”, Madrid, 1905

The reticularist doctrine, supported by C. Golgi, believe that the widespread network of filaments seen in the brain fused into each other. This view was challenged by y Cajal applied the concept of cell theory and said that each neuron is an individual entity and the basic unit of neural circuitry. Neuronal theory eventually won and having established that neurons do not fuse together at any level, the questions of how neurons maintained contact and transmitted signals remained. The neuronal junction was too small to be observed by the microscopes of the time.Many neurophysiologists defended the idea that transmission should be electrical, just like the propagation wave along the axon. While the idea made sense, there were important arguments against this simple picture of the nervous system.

• Information flow along a neural chain is unidirectional — this either occurs between the synapse between one neuron and the dendrite of another (axodendritic) or the synapse between the axon of one neuron and the cell body of another.
• Scientists observed evidence that there were both excitatory and inhibitory synapses. A purely electrical synapse conveying excitation and inhibition would be difficult given that action potentials always have the same potential.
• Scientists also observed a delay in the transmission of impulses through a simple proprioceptive reflex. Electrical transmission should see no delay. A common example of this is the standard knee-jerk response when visiting the doctor.

By the beginning of the 20th century, neuroscientists were convinced that most synapses used chemical transmission. The fundamental proof came in 1921 with experiments carried out by Otto Loewi.

## Discovery of Acetylcholine

Loewi took fluid from one frog heart and applied it to another, slowing the second heart and showing that synaptic signaling used chemical messengers (Image created by Nrets.)

Before the 1920s, it was unclear whether signalling across synapses were electrical or chemical but in 1921, Loewi designed an experiment to answer that question. Loewi claimed that the idea for his experiment came to him in a series of dreams. He took the beating hearts of two frogs. One heart had the vagus nerve attached which acts to lower heart rate while the other had it removed. By electrically stimulating the vagus nerve, Loewi made the first heart beat slower. Loewi then took some of the liquid bathing the first heart and applied it to the second heart causing it to beat slower. This proved that some soluble chemical released by the vagus nerve was controlling and slowing heart rate and not the electrical impulse itself. Loewi called this chemical Vagusstoff and it was later found to be acetylcholine.

Loewi further tested this effect by stimulating the sympathetic nerves to accelerate heart rate. When Loewi bathed the heart with the liquid, it also accelerated the rate of the other heart. This chemical was discovered to be adrenaline.

## The Nobel Prize

Loewi doubted that these neurotransmitters also acted in the somatic nervous system — the nervous system associated with the voluntary control of body movements via skeletal muscles. Research in this area proved much more difficult to carry out but Sir Henry Dale proved this through a series of elegant experiments between 1929 and 1936.

Loewi and Dale, were friends since 1906 and continued their research on neurotransmitters. They shared the Nobel Prize in 1936 for their discoveries.