Free speech zone

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https://en.wikipedia.org/wiki/Free_speech_zone

Free speech zones (also known as First Amendment zones, free speech cages, and protest zones) are areas set aside in public places for the purpose of political protesting. The First Amendment to the United States Constitution states that "Congress shall make no law ... abridging ... the right of the people peaceably to assemble, and to petition the Government for a redress of grievances." The existence of free speech zones is based on U.S. court decisions stipulating that the government may reasonably regulate the time, place, and manner – but not content – of expression.

The Supreme Court has developed a four-part analysis to evaluate the constitutionality of time, place and manner (TPM) restrictions. To pass muster under the First Amendment, TPM restrictions must be neutral with respect to content, be narrowly drawn, serve a significant government interest, and leave open alternative channels of communication. Application of this four-part analysis varies with the circumstances of each case, and typically requires lower standards for the restriction of obscenity and fighting words.

Free speech zones have been used at a variety of political gatherings. The stated purpose of free speech zones is to protect the safety of those attending the political gathering, or for the safety of the protesters themselves. Critics, however, suggest that such zones are "Orwellian", and that authorities use them in a heavy-handed manner to censor protesters by putting them literally out of sight of the mass media, hence the public, as well as visiting dignitaries. Though authorities generally deny specifically targeting protesters, on a number of occasions, these denials have been contradicted by subsequent court testimony. The American Civil Liberties Union (ACLU) has filed, with various degrees of success and failure, a number of lawsuits on the issue.

Although free speech zones existed prior to the presidency of George W. Bush, it was during Bush's presidency that their scope was greatly expanded. These zones continued through the presidency of Barack Obama, who signed a bill in 2012 that expanded the power of the Secret Service to restrict speech and make arrests. Many colleges and universities earlier instituted free-speech-zone rules during the Vietnam-era protests of the 1960s and 1970s. In recent years, a number of them have revised or removed these restrictions following student protests and lawsuits.

History

During the 1988 Democratic National Convention, the city of Atlanta set up a "designated protest zone" so the convention would not be disrupted. A pro-choice demonstrator opposing an Operation Rescue group said Atlanta Mayor Andrew Young "put us in a free-speech cage." "Protest zones" were used during the 1992 and 1996 United States presidential nominating conventions.

Free speech zones have been used for non-political purposes. Through 1990s, the San Francisco International Airport played host to a steady stream of religious groups (Hare Krishnas in particular), preachers, and beggars. The city considered whether this public transportation hub was required to host free speech, and to what extent. As a compromise, two "free speech booths" were installed in the South Terminal, and groups wishing to speak but not having direct business at the airport were directed there. These booths still exist, although permits are required to access the booths.

Police on Union Street in Seattle during the 1999 WTO conference. The WTO protests catalyzed a number of changes in the way law enforcement deals with protesters.

WTO Ministerial Conference of 1999 protest activity saw a number of changes to how law enforcement deals with protest activities. "The [National Lawyers] Guild, which has a 35-year history of monitoring First Amendment activity, has witnessed a notable change in police treatment of political protesters since the November 1999 World Trade Organization meeting in Seattle. At subsequent gatherings in Washington, D.C., Detroit, Philadelphia, Los Angeles, Miami, Chicago, and Portland a pattern of behavior that stifles First Amendment rights has emerged". In a subsequent lawsuit, the United States Court of Appeals for the Ninth Circuit found that "It was lawful for the city of Seattle to deem part of downtown off-limits ... But the court also said that police enforcing the rule may have gone too far by targeting only those opposed to the WTO, in violation of their First Amendment rights."

When then-President George W Bush came to Pittsburgh, Pennsylvania, on Labor Day, 2002, for a speech, the local police, acting on the request of the Secret Service, erected chain-link fence on a baseball field a third of a mile from the speech site, and proclaimed it a "designated free-speech zone."

Free speech zones were used in Boston at the 2004 Democratic National Convention. The free speech zones organized by the authorities in Boston were boxed in by concrete walls, invisible to the FleetCenter where the convention was held and criticized harshly as a "protest pen" or "Boston's Camp X-Ray". "Some protesters for a short time Monday [July 26, 2004] converted the zone into a mock prison camp by donning hoods and marching in the cage with their hands behind their backs." A coalition of groups protesting the Iraq War challenged the planned protest zones. U.S. District Court Judge Douglas Woodlock was sympathetic to their request: "One cannot conceive of what other design elements could be put into a space to create a more symbolic affront to the role of free expression.". However, he ultimately rejected the petition to move the protest zones closer to the FleetCenter.

Free speech zones were also used in New York City at the 2004 Republican National Convention. According to Mike McGuire, a columnist for the online anti-war magazine Nonviolent Activist, "The policing of the protests during the 2004 Republican National Convention represent[ed] another interesting model of repression. The NYPD tracked every planned action and set up traps. As marches began, police would emerge from their hiding places – building vestibules, parking garages, or vans – and corral the dissenters with orange netting that read 'POLICE LINE – DO not CROSS,' establishing areas they ironically called 'ad-hoc free speech zones.' One by one, protesters were arrested and detained – some for nearly two days." Both the Democratic and Republican National parties were jointly awarded a 2005 Jefferson Muzzle from the Thomas Jefferson Center for the Protection of Free Expression, "For their mutual failure to make the preservation of First Amendment freedoms a priority during the last Presidential election".

Falun Gong protesters inside a fenced-off free speech zone at the 2000 Presidential Debate at Washington University in St. Louis

Free speech zones were commonly used by President George W. Bush after the September 11 attacks and through the 2004 election. Free speech zones were set up by the Secret Service, who scouted locations where the U.S. president was scheduled to speak, or pass through. Officials targeted those who carried anti-Bush signs and escorted them to the free speech zones prior to and during the event. Reporters were often barred by local officials from displaying these protesters on camera or speaking to them within the zone. Protesters who refused to go to the free speech zone were often arrested and charged with trespassing, disorderly conduct and/or resisting arrest. A seldom-used federal law making it unlawful to "willfully and knowingly to enter or remain in ... any posted, cordoned off, or otherwise restricted area of a building or grounds where the President or other person protected by the Secret Service is or will be temporarily visiting" has also been invoked.

Criticisms

A "First Amendment Area" at the Muir Woods National Monument.

Civil liberties advocates argue that free speech zones are used as a form of censorship and public relations management to conceal the existence of popular opposition from the mass public and elected officials. There is much controversy surrounding the creation of these areas – the mere existence of such zones is offensive to some people, who maintain that the First Amendment to the United States Constitution makes the entire country an unrestricted free speech zone. The Department of Homeland Security "has even gone so far as to tell local police departments to regard critics of the War on Terrorism as potential terrorists themselves."

The Bush administration has been criticized by columnist James Bovard of The American Conservative for requiring protesters to stay within a designated area, while allowing supporters access to more areas. According to the Chicago Tribune, the American Civil Liberties Union has asked a federal court in Washington, D.C. to prevent the Secret Service from keeping anti-Bush protesters distant from presidential appearances while allowing supporters to display their messages up close, where they are likely to be seen by the news media.

The preliminary plan for the 2004 Democratic National Convention was criticized by the National Lawyers Guild and the ACLU of Massachusetts as being insufficient to handle the size of the expected protest. "The zone would hold as few as 400 of the several thousand protesters who are expected in Boston in late July."

Notable incidents and court proceedings

In 1939, the United States Supreme Court found in Hague v. Committee for Industrial Organization that public streets and parks "have immemorially been held in trust for the use of the public and, time out of mind, have been used for purposes of assembly, communicating thoughts between citizens, and discussing public questions." In the later Thornhill v. Alabama case, the court found that picketing and marching in public areas is protected by the United States Constitution as free speech. However, subsequent rulings – Edwards v. South Carolina, Brown v. Louisiana, Cox v. Louisiana, and Adderley v. Florida – found that picketing is afforded less protection than pure speech due to the physical externalities it creates. Regulations on demonstrations may affect the time, place, and manner of those demonstrations, but may not discriminate based on the content of the demonstration.

The Secret Service denied targeting the president's political opponents. "Decisions made in the formulation of a security plan are based on security considerations, not political considerations", said one Secret Service spokesman.

Bill Neel

"These [free speech] zones routinely succeed in keeping protesters out of presidential sight and outside the view of media covering the event. When Bush came to the Pittsburgh area on Labor Day 2002, 65-year-old retired steel worker Bill Neel was there to greet him with a sign proclaiming, 'The Bush family must surely love the poor, they made so many of us.' The local police, at the Secret Service's behest, set up a 'designated free-speech zone' on a baseball field surrounded by a chain-link fence a third of a mile from the location of Bush's speech. The police cleared the path of the motorcade of all critical signs, though folks with pro-Bush signs were permitted to line the president's path. Neel refused to go to the designated area and was arrested for disorderly conduct. Police detective John Ianachione testified that the Secret Service told local police to confine 'people that were there making a statement pretty much against the president and his views.'" District judge Shirley Trkula threw out the charges, stating that "I believe this is America. Whatever happened to 'I don't agree with you, but I'll defend to the death your right to say it'?"

Brett Bursey

At another incident during a presidential visit to South Carolina, protester Brett Bursey refused an order by Secret Service agents to go to a free speech zone half-a-mile away. He was arrested and charged with trespassing by the South Carolina police. "Bursey said that he asked the policeman if 'it was the content of my sign,' and he said, 'Yes, sir, it's the content of your sign that's the problem.'" However, the prosecution, led by James Strom Thurmond Jr., disputes Bursey's version of events. Trespassing charges against Bursey were dropped, and Bursey was instead indicted by the federal government for violation of a federal law that allows the Secret Service to restrict access to areas visited by the president. Bursey faced up to six months in prison and a US$5,000 fine. After a bench trial, Bursey was convicted of the offense of trespassing, but judge Bristow Marchant deemed the offense to be relatively minor and ordered a fine of $500 be assessed, which Bursey appealed, and lost. In his ruling, Marchant found that "this is not to say that the Secret Service's power to restrict the area around the President is absolute, nor does the Court find that protesters are required to go to a designated demonstration area – which was an issue in this case – as long as they do not otherwise remain in a properly restricted area."

Marchant's ruling however, was criticized for three reasons:

• The ruling found that Bursey was not the victim of selective prosecution because Bursey was the only person who had refused an order to leave the area. However, this overlooks the fact that nobody else refused to leave the zone because nobody else was asked to leave.
• The prosecution claimed that the protected zone around the President was 100 yards wide. However, it was unmarked, with cars and trucks allowed to pass through and drop off ticket-holders, and nobody was willing to tell protesters where the zone's boundaries were. Marchant's decision noted this but did not find this unreasonable.
• Marchant found that in the "age of suicide bombers", the Secret Service should have latitude to get rid of anyone suspicious who is standing near the president's route. However, given that the reason Bursey was singled out by the Secret Service was his sign, "it's enough to make anyone with a dissenting view think twice before deciding to stand out from a crowd."

ACLU litigation

In 2003, the ACLU brought a lawsuit against the Secret Service, ACORN v. Secret Service, representing the Association of Community Organizations for Reform Now (ACORN). "The federal court in Philadelphia dismissed that case in March [2004] after the Secret Service acknowledged that it could not discriminate against protesters through the use of out-of-sight, out-of-earshot protest zones." Another 2003 lawsuit against the city of Philadelphia, ACORN v. Philadelphia, charged that the Philadelphia Police Department, on orders from the Secret Service, had kept protesters "further away from the site of presidential visits than Administration supporters. A high-ranking official of the Philadelphia police told ACLU of Pennsylvania Legal Director Stefan Presser that he was only following Secret Service orders." However, the court found the ACLU lacked standing to bring the case and dismissed it.

The Secret Service says it does establish 'public viewing areas' to protect dignitaries but does not discriminate against individuals based on the content of their signs or speech. 'Absolutely not,' said Tom Mazur, a spokesman for the agency created to protect the president. 'The Secret Service makes no distinction on the purpose, message or intent of any individual or group.' Civil libertarians dispute that. They cite a Corpus Christi, Texas, couple, Jeff and Nicole Rank, as an example. The two were arrested at a Bush campaign event in Charleston, West Virginia, on July 4, 2004, when they refused to take off anti-Bush shirts. Their shirts read, 'Love America, Hate Bush' ... The ACLU found 17 cases since March 2001 in which protesters were removed during events where the president or vice president appeared. And lawyers say it's an increasing trend.

According to Jeff Rank, Nicole Rank's shirt did say "Love America, Hate Bush" while Jeff Rank's shirt said "Regime change starts at home."

The incident occurred several months after the Secret Service's pledge in ACORN v. Secret Service not to discriminate against protesters. "The charges against the Ranks were ultimately dismissed in court and the mayor and city council publicly apologized for the arrest. City officials also said that local law enforcement was acting at the request of Secret Service." ACLU Senior Staff Attorney Chris Hansen pointed out that "The Secret Service has promised to not curtail the right to dissent at presidential appearances, and yet we are still hearing stories of people being blocked from engaging in lawful protest", said Hansen. "It is time for the Secret Service to stop making empty promises." The Ranks subsequently filed a lawsuit, Rank v. Jenkins, against Deputy Assistant to the President Gregory Jenkins and the Secret Service. "The lawsuit, Rank v. Jenkins, is seeking unspecified damages as well as a declaration that the actions leading to the removal of the Ranks from the Capitol grounds were unconstitutional." In August 2007, the Ranks settled their lawsuit against the Federal Government. The government paid them $80,000, but made no admission of wrongdoing. The Ranks' case against Gregory Jenkins is still pending in the District of Columbia.

As a result of ACLU subpoenas during the discovery in the Rank lawsuit, the ACLU obtained the White House's previously-classified presidential advance manual. The manual gives people organizing presidential visits specific advice for preventing or obstructing protests. "There are several ways the advance person" – the person organizing the presidential visit – "can prepare a site to minimize demonstrators. First, as always, work with the Secret Service to and have them ask the local police department to designate a protest area where demonstrators can be placed, preferably not in view of the event site or motorcade route. The formation of 'rally squads' is a common way to prepare for demonstrators ... The rally squad's task is to use their signs and banners as shields between the demonstrators and the main press platform ... As a last resort, security should remove the demonstrators from the event site."

College and university campuses

The free speech area on the campus of Texas Woman's University (above) and the sign that demarcates it (below).

 

The use of free speech zones on university campuses is controversial. Many universities created on-campus free speech zones during the 1960s and 1970s, during which protests on-campus (especially against the Vietnam War) were common. Generally, the requirements are that the university is given advance notice and that they are held in locations that do not disrupt classes.

In 1968, the Supreme Court ruled in Tinker v. Des Moines Independent Community School District that non-disruptive speech is permitted in public schools. However, this does not apply to private universities. In September 2004, U.S. District Court Judge Sam Cummings struck down the free-speech-zone policy at Texas Tech University.

According to the opinion of the court, campus areas such as parks, sidewalks, streets and other areas are designated as public forums, regardless of whether the university has chosen to officially designate the areas as such. The university may open more of the campus as public forums for its students, but it cannot designate fewer areas ... Not all places within the boundaries of the campus are public forums, according to Cummings' opinion. The court declared the university's policy unconstitutional to the extent that it regulates the content of student speech in areas of the campus that are public forums.

In 2007, the Foundation for Individual Rights in Education released a survey of 346 colleges and Universities in the United States. Of those institutions, 259 (75%) maintain policies that "both clearly and substantially restrict freedom of speech."

In December 2005, the College Libertarians at the University of North Carolina at Greensboro staged a protest outside the University's designated protest zones. The specific intent of the protest was to provoke just such a charge, to "provoke the system into action into a critical review of what's going on." Two students, Allison Jaynes and Robert Sinnott, were brought up on charges under the student code of conduct of "violation of respect", for refusing to move when told to do so by a university official. The university subsequently dropped honor code charges against the students. "University officials said the history of the free-speech zones is not known. 'It predated just about everybody here", said Lucien 'Skip' Capone III, the university attorney. The policy may be a holdover from the Vietnam War and civil rights era, he said.'"

A number of colleges and universities have revised or revoked free speech zone policies in the last decade, including: Tufts University, Appalachian State University, and West Virginia University. In August 2006, Penn State University revised its seven-year-old rules restricting the rights of students to protest. "In effect, the whole campus is now a 'free-speech zone.'"

Controversies have also occurred at the University of Southern California, Indiana University, the University of Nevada, Las Vegas, and Brigham Young University.

At Marquette University, an unattributed Dave Barry quote was attached to the door of the office that graduate student Stuart Ditsler shared with three other teaching assistants. It read, "As Americans we must always remember that we all have a common enemy, an enemy that is dangerous, powerful, and relentless. I refer, of course, to the federal government." Philosophy department chairman James South ordered Ditsler to remove the quote, calling it patently offensive. South claimed that the University's free-speech zone rules required Ditsler to take it down. University spokeswoman Brigid O'Brien Miller stated that it was "a workplace issue, not one of academic freedom." Ultimately, the quote was allowed to remain, albeit with attribution.

For example, the Louisiana State University Free Speech Alley (or Free Speech Plaza) was used in November 2015 when Louisiana gubernatorial candidate John Bel Edwards was publicly endorsed by former opponent and Republican Lt. Governor Jay Dardenne. The Consuming Fire Fellowship, a church located in rural Woodville, Mississippi, often sends members to convene at the university's Free Speech Alley to preach their views of Christianity. The members have often been met with strong resistance and resentment by the student body. Ivan Imes, a retired engineer who holds "Jesus Talks" for students at the university, said in an interview that he advised students frustrated with the preachings of the Consuming Fire Fellowship, "to give the church a break. They don't understand love. They don't understand forgiveness. There are a lot of things in the Bible that they don’t understand, or at least don’t live out."

As of March 2017, four states had passed legislation outlawing public colleges and universities from establishing free speech zones. The first state to do so was Virginia in 2014, followed by Missouri in 2015, Arizona in 2016, and Kentucky in 2017.

Other countries

Designated protest areas were established during the August 2007 Security and Prosperity Partnership of North America Summit in Ottawa, Canada. Although use of the areas was voluntary and not surrounded by fences, some protesters decried the use of designated protest areas, calling them "protest pens."

During the 2005 WTO Hong Kong Ministerial Conference, over 10,000 protesters were present. Wan Chai Sports Ground and Wan Chai Cargo Handling Basin were designated as protest zones. Police wielded sticks, used gas grenades and shot rubber bullets at some of the protesters. They arrested 910 people, 14 were charged, but none were convicted.

Three protest parks were designated in Beijing during the 2008 Summer Olympics, at the suggestion of the IOC. All 77 applications to protest there were withdrawn or denied, and no protests took place. Four people who applied to protest were arrested or sentenced to "re-education through labor".

In the Philippines, public spaces that are designated as free speech zones are called freedom parks.

Planck units

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Planck_units 

In particle physics and physical cosmology, Planck units are a system of units of measurement defined exclusively in terms of four universal physical constants: c, G, ħ, and k_B (described further below). Expressing one of these physical constants in terms of Planck units yields a numerical value of 1. They are a system of natural units, defined using fundamental properties of nature (specifically, properties of free space) rather than properties of a chosen prototype object. Originally proposed in 1899 by German physicist Max Planck, they are relevant in research on unified theories such as quantum gravity.

The term Planck scale refers to quantities of space, time, energy and other units that are similar in magnitude to corresponding Planck units. This region may be characterized by particle energies of around 10¹⁹ GeV or 10⁹ J, time intervals of around 5×10⁻⁴⁴ s and lengths of around 10⁻³⁵ m (approximately the energy-equivalent of the Planck mass, the Planck time and the Planck length, respectively). At the Planck scale, the predictions of the Standard Model, quantum field theory and general relativity are not expected to apply, and quantum effects of gravity are expected to dominate. One example is represented by the conditions in the first 10⁻⁴³ seconds of our universe after the Big Bang, approximately 13.8 billion years ago.

The four universal constants that, by definition, have a numeric value 1 when expressed in these units are:

• c, the speed of light in vacuum,
• G, the gravitational constant,
• ħ, the reduced Planck constant, and
• k_B, the Boltzmann constant.

Variants of the basic idea of Planck units exist, such as alternate choices of normalization that give other numeric values to one or more of the four constants above.

Introduction

Any system of measurement may be assigned a mutually independent set of base quantities and associated base units, from which all other quantities and units may be derived. In the International System of Units, for example, the SI base quantities include length with the associated unit of the metre. In the system of Planck units, a similar set of base quantities and associated units may be selected, in terms of which other quantities and coherent units may be expressed. The Planck unit of length has become known as the Planck length, and the Planck unit of time is known as the Planck time, but this nomenclature has not been established as extending to all quantities.

All Planck units are derived from the dimensional universal physical constants that define the system, and in a convention in which these units are omitted (i.e. treated as having the dimensionless value 1), these constants are then eliminated from equations of physics in which they appear. For example, Newton's law of universal gravitation,

${\displaystyle F=G\frac{m_1{m}_2}{r^2}=\left(\frac{F_{\text{P}}{l}_{\text{P}}^2}{m_{\text{P}}^2}\right)\frac{m_1{m}_2}{r^2}}$,

can be expressed as:

${\displaystyle \frac{F}{F_{\text{P}}}=\frac{\left({\displaystyle \frac{m_1}{m_{\text{P}}}}\right)\left({\displaystyle \frac{m_2}{m_{\text{P}}}}\right)}{{\left({\displaystyle \frac{r}{l_{\text{P}}}}\right)}^2}}$.

Both equations are dimensionally consistent and equally valid in any system of quantities, but the second equation, with G absent, is relating only dimensionless quantities since any ratio of two like-dimensioned quantities is a dimensionless quantity. If, by a shorthand convention, it is understood that each physical quantity is the corresponding ratio with a coherent Planck unit (or "expressed in Planck units"), the ratios above may be expressed simply with the symbols of physical quantity, without being scaled explicitly by their corresponding unit:

${\displaystyle F^{\prime }=\frac{m_1^{\prime }{m}_2^{\prime }}{r^{\prime 2}}}$.

This last equation (without G) is valid with F′, m₁′, m₂′, and r′ being the dimensionless ratio quantities corresponding to the standard quantities, written e.g. F′ ≘ F or F′ = F/F_P, but not as a direct equality of quantities. This may seem to be "setting the constants c, G, etc., to 1" if the correspondence of the quantities is thought of as equality. For this reason, Planck or other natural units should be employed with care. Referring to "G = c = 1", Paul S. Wesson wrote that, "Mathematically it is an acceptable trick which saves labour. Physically it represents a loss of information and can lead to confusion."

History and definition

The concept of natural units was introduced in 1874, when George Johnstone Stoney, noting that electric charge is quantized, derived units of length, time, and mass, now named Stoney units in his honor. Stoney chose his units so that G, c, and the electron charge e would be numerically equal to 1. In 1899, one year before the advent of quantum theory, Max Planck introduced what became later known as the Planck constant. At the end of the paper, he proposed the base units that were later named in his honor. The Planck units are based on the quantum of action, now usually known as the Planck constant, which appeared in the Wien approximation for black-body radiation. Planck underlined the universality of the new unit system, writing:

... die Möglichkeit gegeben ist, Einheiten für Länge, Masse, Zeit und Temperatur aufzustellen, welche, unabhängig von speciellen Körpern oder Substanzen, ihre Bedeutung für alle Zeiten und für alle, auch ausserirdische und aussermenschliche Culturen nothwendig behalten und welche daher als »natürliche Maasseinheiten« bezeichnet werden können.

... it is possible to set up units for length, mass, time and temperature, which are independent of special bodies or substances, necessarily retaining their meaning for all times and for all civilizations, including extraterrestrial and non-human ones, which can be called "natural units of measure".

Planck considered only the units based on the universal constants ${\displaystyle G}$, ${\displaystyle h}$, ${\displaystyle c}$, and ${\displaystyle k_{\mathrm{B}}}$ to arrive at natural units for length, time, mass, and temperature. His definitions differ from the modern ones by a factor of ${\displaystyle \sqrt{2\pi }}$, because the modern definitions use ${\displaystyle \hslash }$ rather than ${\displaystyle h}$.

Table 1: Modern values for Planck's original choice of quantities

Name	Dimension	Expression	Value (SI units)
Planck length	length (L)	${\displaystyle l_{\text{P}}=\sqrt{\frac{\hslash G}{c^3}}}$	1.616255(18)×10−35 m
Planck mass	mass (M)	${\displaystyle m_{\text{P}}=\sqrt{\frac{\hslash c}{G}}}$	2.176434(24)×10−8 kg
Planck time	time (T)	${\displaystyle t_{\text{P}}=\sqrt{\frac{\hslash G}{c^5}}}$	5.391247(60)×10−44 s
Planck temperature	temperature (Θ)	${\displaystyle T_{\text{P}}=\sqrt{\frac{\hslash c^5}{G{k}_{\text{B}}^2}}}$	1.416784(16)×1032 K

Unlike the case with the International System of Units, there is no official entity that establishes a definition of a Planck unit system. Some authors define the base Planck units to be those of mass, length and time, regarding an additional unit for temperature to be redundant. Other tabulations add, in addition to a unit for temperature, a unit for electric charge, so that either the Coulomb constant ${\displaystyle k_{\text{e}}}$ or the vacuum permittivity ${\displaystyle {ϵ}_0}$ is normalized to 1. Thus, depending on the author's choice, this charge unit is given by $${\displaystyle q_{\text{P}}=\sqrt{4\pi {ϵ}_0\hslash c}\approx 1.875546\times {10}^{-18}\text{ C}\approx 11.7e}$$ for ${\displaystyle k_{\text{e}}=1}$, or $${\displaystyle q_{\text{P}}=\sqrt{{ϵ}_0\hslash c}\approx 5.290818\times {10}^{-19}\text{ C}\approx 3.3e}$$ for ${\displaystyle {\epsilon }_0=1}$. Some of these tabulations also replace mass with energy when doing so.

In SI units, the values of c, h, e and k_B are exact and the values of ε₀ and G in SI units respectively have relative uncertainties of 1.6×10⁻¹⁰ and 2.2×10⁻⁵. Hence, the uncertainties in the SI values of the Planck units derive almost entirely from uncertainty in the SI value of G.

Compared to Stoney units, Planck base units are all larger by a factor $\sqrt{1/\alpha }\approx 11.7$, where ${\displaystyle \alpha }$ is the fine-structure constant.

Derived units

In any system of measurement, units for many physical quantities can be derived from base units. Table 2 offers a sample of derived Planck units, some of which are seldom used. As with the base units, their use is mostly confined to theoretical physics because most of them are too large or too small for empirical or practical use and there are large uncertainties in their values.

Table 2: Coherent derived units of Planck units

Derived unit of	Expression	Approximate SI equivalent
area (L2)	${\displaystyle l_{\text{P}}^2=\frac{\hslash G}{c^3}}$	2.6121×10−70 m2
volume (L3)	${\displaystyle l_{\text{P}}^3={\left(\frac{\hslash G}{c^3}\right)}^{\frac{3}{2}}=\sqrt{\frac{(\hslash G{)}^3}{c^9}}}$	4.2217×10−105 m3
momentum (LMT−1)	${\displaystyle m_{\text{P}}c=\frac{\hslash }{l_{\text{P}}}=\sqrt{\frac{\hslash c^3}{G}}}$	6.5249 kg⋅m/s
energy (L2MT−2)	${\displaystyle E_{\text{P}}=m_{\text{P}}{c}^2=\frac{\hslash }{t_{\text{P}}}=\sqrt{\frac{\hslash c^5}{G}}}$	1.9561×109 J
force (LMT−2)	${\displaystyle F_{\text{P}}=\frac{E_{\text{P}}}{l_{\text{P}}}=\frac{\hslash }{l_{\text{P}}{t}_{\text{P}}}=\frac{c^4}{G}}$	1.2103×1044 N
density (L−3M)	${\displaystyle {\rho }_{\text{P}}=\frac{m_{\text{P}}}{l_{\text{P}}^3}=\frac{\hslash t_{\text{P}}}{l_{\text{P}}^5}=\frac{c^5}{\hslash G^2}}$	5.1550×1096 kg/m3
acceleration (LT−2)	${\displaystyle a_{\text{P}}=\frac{c}{t_{\text{P}}}=\sqrt{\frac{c^7}{\hslash G}}}$	5.5608×1051 m/s2

Some Planck units, such as of time and length, are many orders of magnitude too large or too small to be of practical use, so that Planck units as a system are typically only relevant to theoretical physics. In some cases, a Planck unit may suggest a limit to a range of a physical quantity where present-day theories of physics apply. For example, our understanding of the Big Bang does not extend to the Planck epoch, i.e., when the universe was less than one Planck time old. Describing the universe during the Planck epoch requires a theory of quantum gravity that would incorporate quantum effects into general relativity. Such a theory does not yet exist.

Several quantities are not "extreme" in magnitude, such as the Planck mass, which is about 22 micrograms: very large in comparison with subatomic particles, and within the mass range of living organisms. Similarly, the related units of energy and of momentum are in the range of some everyday phenomena.

Significance

Planck units have little anthropocentric arbitrariness, but do still involve some arbitrary choices in terms of the defining constants. Unlike the metre and second, which exist as base units in the SI system for historical reasons, the Planck length and Planck time are conceptually linked at a fundamental physical level. Consequently, natural units help physicists to reframe questions. Frank Wilczek puts it succinctly:

We see that the question [posed] is not, "Why is gravity so feeble?" but rather, "Why is the proton's mass so small?" For in natural (Planck) units, the strength of gravity simply is what it is, a primary quantity, while the proton's mass is the tiny number 1/13 quintillion.

While it is true that the electrostatic repulsive force between two protons (alone in free space) greatly exceeds the gravitational attractive force between the same two protons, this is not about the relative strengths of the two fundamental forces. From the point of view of Planck units, this is comparing apples with oranges, because mass and electric charge are incommensurable quantities. Rather, the disparity of magnitude of force is a manifestation of the fact that the charge on the protons is approximately the unit charge but the mass of the protons is far less than the unit mass.

When Planck proposed his units, the goal was only that of establishing a universal ("natural") way of measuring objects, without giving any special meaning to quantities that measured one single unit. However, in 1959, C. A. Mead showed that distances that measured one Planck length, or, similarly, times that measured one Planck time, did carry special implications related to Heisenberg's uncertainty principle:

An analysis of the effect of gravitation on hypothetical experiments indicates that it is impossible to measure the position of a particle with error less than 𝛥⁢𝑥 ≳ √𝐺 = 1.6 × 10⁻³³ cm, where 𝐺 is the gravitational constant in natural units. A similar limitation applies to the precise synchronization of clocks.

Planck scale

In particle physics and physical cosmology, the Planck scale is an energy scale around 1.22×10²⁸ eV (the Planck energy, corresponding to the energy equivalent of the Planck mass, 2.17645×10⁻⁸ kg) at which quantum effects of gravity become significant. At this scale, present descriptions and theories of sub-atomic particle interactions in terms of quantum field theory break down and become inadequate, due to the impact of the apparent non-renormalizability of gravity within current theories.

Relationship to gravity

At the Planck length scale, the strength of gravity is expected to become comparable with the other forces, and it has been theorized that all the fundamental forces are unified at that scale, but the exact mechanism of this unification remains unknown. The Planck scale is therefore the point at which the effects of quantum gravity can no longer be ignored in other fundamental interactions, where current calculations and approaches begin to break down, and a means to take account of its impact is necessary. On these grounds, it has been speculated that it may be an approximate lower limit at which a black hole could be formed by collapse.

While physicists have a fairly good understanding of the other fundamental interactions of forces on the quantum level, gravity is problematic, and cannot be integrated with quantum mechanics at very high energies using the usual framework of quantum field theory. At lesser energy levels it is usually ignored, while for energies approaching or exceeding the Planck scale, a new theory of quantum gravity is necessary. Approaches to this problem include string theory and M-theory, loop quantum gravity, noncommutative geometry, and causal set theory.

In cosmology

Main article: Chronology of the universe

Further information: Time-variation of fundamental constants

In Big Bang cosmology, the Planck epoch or Planck era is the earliest stage of the Big Bang, before the time passed was equal to the Planck time, t_P, or approximately 10⁻⁴³ seconds. There is no currently available physical theory to describe such short times, and it is not clear in what sense the concept of time is meaningful for values smaller than the Planck time. It is generally assumed that quantum effects of gravity dominate physical interactions at this time scale. At this scale, the unified force of the Standard Model is assumed to be unified with gravitation. Immeasurably hot and dense, the state of the Planck epoch was succeeded by the grand unification epoch, where gravitation is separated from the unified force of the Standard Model, in turn followed by the inflationary epoch, which ended after about 10⁻³² seconds (or about 10¹¹ t_P).

Table 3 lists properties of the observable universe today expressed in Planck units.

Table 3: Today's universe in Planck units

Property of present-day observable universe	Approximate number of Planck units	Equivalents
Age	8.08 × 1060 tP	4.35 × 1017 s or 1.38 × 1010 years
Diameter	5.4 × 1061 lP	8.7 × 1026 m or 9.2 × 1010 light-years
Mass	approx. 1060 mP	3 × 1052 kg or 1.5 × 1022 solar masses (only counting stars) 1080 protons (sometimes known as the Eddington number)
Density	1.8 × 10−123 mP⋅lP−3	9.9 × 10−27 kg⋅m−3
Temperature	1.9 × 10−32 TP	2.725 K temperature of the cosmic microwave background radiation
Cosmological constant	≈ 10−122 l −2 P	≈ 10−52 m−2
Hubble constant	≈ 10−61 t −1 P	≈ 10−18 s−1 ≈ 102 (km/s)/Mpc

After the measurement of the cosmological constant (Λ) in 1998, estimated at 10⁻¹²² in Planck units, it was noted that this is suggestively close to the reciprocal of the age of the universe (T) squared. Barrow and Shaw proposed a modified theory in which Λ is a field evolving in such a way that its value remains Λ ~ T⁻² throughout the history of the universe.

Analysis of the units

Planck length

The Planck length, denoted ℓ_P, is a unit of length defined as:$${\displaystyle {\ell }_{\mathrm{P}}=\sqrt{\frac{\hslash G}{c^3}}}$$

It is equal to 1.616255(18)×10⁻³⁵ m (the two digits enclosed by parentheses are the estimated standard error associated with the reported numerical value) or about 10⁻²⁰ times the diameter of a proton. It can be motivated in various ways, such as considering a particle whose reduced Compton wavelength is comparable to its Schwarzschild radius, though whether those concepts are in fact simultaneously applicable is open to debate. (The same heuristic argument simultaneously motivates the Planck mass.)

The Planck length is a distance scale of interest in speculations about quantum gravity. The Bekenstein–Hawking entropy of a black hole is one-fourth the area of its event horizon in units of Planck length squared. Since the 1950s, it has been conjectured that quantum fluctuations of the spacetime metric might make the familiar notion of distance inapplicable below the Planck length. This is sometimes expressed by saying that "spacetime becomes a foam at the Planck scale". It is possible that the Planck length is the shortest physically measurable distance, since any attempt to investigate the possible existence of shorter distances, by performing higher-energy collisions, would result in black hole production. Higher-energy collisions, rather than splitting matter into finer pieces, would simply produce bigger black holes.

The strings of string theory are modeled to be on the order of the Planck length. In theories with large extra dimensions, the Planck length calculated from the observed value of ${\displaystyle G}$ can be smaller than the true, fundamental Planck length.

Planck time

The Planck time t_P is the time required for light to travel a distance of 1 Planck length in vacuum, which is a time interval of approximately 5.39×10⁻⁴⁴ s. No current physical theory can describe timescales shorter than the Planck time, such as the earliest events after the Big Bang. Some conjectures state that the structure of time need not remain smooth on intervals comparable to the Planck time.

Planck energy

The Planck energy E_P is approximately equal to the energy released in the combustion of the fuel in an automobile fuel tank (57.2 L at 34.2 MJ/L of chemical energy). The ultra-high-energy cosmic ray observed in 1991 had a measured energy of about 50 J, equivalent to about 2.5×10⁻⁸ E_P.

Proposals for theories of doubly special relativity posit that, in addition to the speed of light, an energy scale is also invariant for all inertial observers. Typically, this energy scale is chosen to be the Planck energy.

Planck unit of force

The Planck unit of force may be thought of as the derived unit of force in the Planck system if the Planck units of time, length, and mass are considered to be base units. $${\displaystyle F_{\text{P}}=\frac{m_{\text{P}}c}{t_{\text{P}}}=\frac{c^4}{G}\approx 1.2103\times {10}^{44}\mathrm{N}}$$

It is the gravitational attractive force of two bodies of 1 Planck mass each that are held 1 Planck length apart. One convention for the Planck charge is to choose it so that the electrostatic repulsion of two objects with Planck charge and mass that are held 1 Planck length apart balances the Newtonian attraction between them.

Some authors have argued that the Planck force is on the order of the maximum force that can occur between two bodies. However, the validity of these conjectures has been disputed.

Planck temperature

The Planck temperature T_P is 1.416784(16)×10³² K. At this temperature, the wavelength of light emitted by thermal radiation reaches the Planck length. There are no known physical models able to describe temperatures greater than T_P; a quantum theory of gravity would be required to model the extreme energies attained. Hypothetically, a system in thermal equilibrium at the Planck temperature might contain Planck-scale black holes, constantly being formed from thermal radiation and decaying via Hawking evaporation. Adding energy to such a system might decrease its temperature by creating larger black holes, whose Hawking temperature is lower.

Nondimensionalized equations

Physical quantities that have different dimensions (such as time and length) cannot be equated even if they are numerically equal (e.g., 1 second is not the same as 1 metre). In theoretical physics, however, this scruple may be set aside, by a process called nondimensionalization. The effective result is that many fundamental equations of physics, which often include some of the constants used to define Planck units, become equations where these constants are replaced by a 1.

Examples include the energy–momentum relation E² = (mc²)² + (pc)², which becomes E² = m² + p², and the Dirac equation (iħγ^μ∂_μ − mc)ψ = 0, which becomes (iγ^μ∂_μ − m)ψ = 0.

Alternative choices of normalization

As already stated above, Planck units are derived by "normalizing" the numerical values of certain fundamental constants to 1. These normalizations are neither the only ones possible nor necessarily the best. Moreover, the choice of what factors to normalize, among the factors appearing in the fundamental equations of physics, is not evident, and the values of the Planck units are sensitive to this choice.

The factor 4π is ubiquitous in theoretical physics because in three-dimensional space, the surface area of a sphere of radius r is 4πr². This, along with the concept of flux, are the basis for the inverse-square law, Gauss's law, and the divergence operator applied to flux density. For example, gravitational and electrostatic fields produced by point objects have spherical symmetry, and so the electric flux through a sphere of radius r around a point charge will be distributed uniformly over that sphere. From this, it follows that a factor of 4πr² will appear in the denominator of Coulomb's law in rationalized form. (Both the numerical factor and the power of the dependence on r would change if space were higher-dimensional; the correct expressions can be deduced from the geometry of higher-dimensional spheres.) Likewise for Newton's law of universal gravitation: a factor of 4π naturally appears in Poisson's equation when relating the gravitational potential to the distribution of matter.

Hence a substantial body of physical theory developed since Planck's 1899 paper suggests normalizing not G but 4πG (or 8πG) to 1. Doing so would introduce a factor of ⁠1/4π⁠ (or ⁠1/8π⁠) into the nondimensionalized form of the law of universal gravitation, consistent with the modern rationalized formulation of Coulomb's law in terms of the vacuum permittivity. In fact, alternative normalizations frequently preserve the factor of ⁠1/4π⁠ in the nondimensionalized form of Coulomb's law as well, so that the nondimensionalized Maxwell's equations for electromagnetism and gravitoelectromagnetism both take the same form as those for electromagnetism in SI, which do not have any factors of 4π. When this is applied to electromagnetic constants, ε₀, this unit system is called "rationalized". When applied additionally to gravitation and Planck units, these are called rationalized Planck units and are seen in high-energy physics.

The rationalized Planck units are defined so that c = 4πG = ħ = ε₀ = k_B = 1.

There are several possible alternative normalizations.

Gravitational constant

In 1899, Newton's law of universal gravitation was still seen as exact, rather than as a convenient approximation holding for "small" velocities and masses (the approximate nature of Newton's law was shown following the development of general relativity in 1915). Hence Planck normalized to 1 the gravitational constant G in Newton's law. In theories emerging after 1899, G nearly always appears in formulae multiplied by 4π or a small integer multiple thereof. Hence, a choice to be made when designing a system of natural units is which, if any, instances of 4π appearing in the equations of physics are to be eliminated via the normalization.

• Normalizing 4πG to 1 (and therefore setting G = ⁠1/4π⁠):
  • Gauss's law for gravity becomes Φ_g = −M (rather than Φ_g = −4πM in Planck units).
  • Eliminates 4πG from the Poisson equation.
  • Eliminates 4πG in the gravitoelectromagnetic (GEM) equations, which hold in weak gravitational fields or locally flat spacetime. These equations have the same form as Maxwell's equations (and the Lorentz force equation) of electromagnetism, with mass density replacing charge density, and with ⁠1/4πG⁠ replacing ε₀.
  • Normalizes the characteristic impedance Z_g of gravitational radiation in free space to 1 (normally expressed as ⁠4πG/c⁠).^{[note 2]}
  • Eliminates 4πG from the Bekenstein–Hawking formula (for the entropy of a black hole in terms of its mass m_BH and the area of its event horizon A_BH) which is simplified to S_BH = πA_BH = (m_BH)².
• Setting 8πG = 1 (and therefore setting G = ⁠1/8π⁠). This would eliminate 8πG from the Einstein field equations, Einstein–Hilbert action, and the Friedmann equations, for gravitation. Planck units modified so that 8πG = 1 are known as reduced Planck units, because the Planck mass is divided by √8π. Also, the Bekenstein–Hawking formula for the entropy of a black hole simplifies to S_BH = (m_BH)²/2 = 2πA_BH.