الصفر المطلق

(تم التحويل من Absolute zero)
هذا المقال هو عن the minimum temperature limit. إذا كنت تريد other uses، انظر Absolute Zero (disambiguation).
Zero kelvin (−273.15 °C) is defined as absolute zero.

الصفر المطلق تعني الحالة التي تكون درجة حرارة المادة فيها أقل ما يمكن ان تصل اليه. وتقضي بان ذرات أوجزيئات المادة تكون لها أقل طاقة في تلك الحالة. اكتشف العلماء ان أقل درجة حرارة يمكن الوصول اليها هي 273.15 درجة سيلزيوس تحت الصفر. تم الوصول إلى معرفة هذا القياس بالاعتماد على العلاقة الطردية بين درجة حرارة غاز ما وضغطه وبالتجربة تبين أن ضغط الغاز يساوي صفرا عند درجة حرارة 273.15 درجة سيلسيوس تحت الصفر.
يسمى مقياس الحرارة الذي له قيمة صفر عند درجة الصفر المطلق بمقياس حرارة مطلق. وهناك مقياس واحد يطابق هذا الوصف وهو مقياس كلفن. الرقم صفر على هذا المقياس يساوي الصفر المطلق أو (0 كلفن) ولا تستعمل كلمة درجة للقياس به.
مقياس كلفن مرتبط بمقياس سيلزيوس حيث ان كل واحد درجة سيلزيوس تساوي واحد كلفن، ولكن الفرق سيلزيوس يبدأ عد درجات الحرارة من -273.15 أما كلفن فيبدأ من 0، وهكذا يمكن معرفة درجة حرارة سيلسيوس من كلفن بتنقيص 273.15 من كلفن والعكس بالعكس. فاذا افترضنا ان درجة حرارة مادة تساوي 50 كلفن فانها تساوي أيضا 50-273.15 فيكون الناتج -223.15 درجة سيلسيوس.
يعتقد الفيزيائيين ان درجة الحرارة لا يمكن ان تصل إلى الصفر المطلق تماما، وأقل درجة حرارة تم الوصول اليها هي واحد في الالف مليون من الدرجة تحت الصفر المطلق.ويحاولون العلماء لان اثبات عمليا الصفر المطلق للغاز والذى تنعدم عندة ضغط الغاز وحجمة على تدرج كلفن.

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بعض مقاييس درجات الحرارة

وهناك عدة أنواع من الترمومترات تيعا لنوع الماة الترمومترية المستخدمة ,فمنها الترمومتر السائل , والترمومتر الغازي والترمومتر الصلب. وفي جميع الأنواع يتم اختيار صفة فيزيائية تتغير بتغير درجة الحرارة(الحجم, ضغط. كثافة ,مقاومة) ومن خلال قياس التغير في هذه الصفة يمكن تعيين درجة الحرارة. ولكي تحدد الترمومترات المختلفة نفس درجة الحرارة تدرج بناء على نقاط مختارة لاجسام تكون درجة حرارتها ثابتة دائما في الظروف المعتادة مثل درجة انصهار الجليد ودرجة غليان الماء تحت الضغط العياري وبناء على ذلك فهناك عدة تدريجات:

1- التدريج السيليزي (Celsius Scale) :

صممه العلم السويدي أندرس سلسيوس وفيه اعتبر درجة انصهار الجليد تحت الضغط العياري هي الصفر. ودرجة غليان الماء تحت الضغط العياري هي 100° وقسم المسافة بينهما إلى 100 قسم متساو, كل قسم يعادل درجة واحدة سيليزية.

2- التدريج الفهرنهيتي (Fahrenheit Scale) :

صممه العالم جابريل فارنهايت، حيث اعتبر أبرد درجة حرارة في انجلترا (وتبلغ -20° س) هي الصفر, ودرجة حرارة الانسان هي 100° وقسم المسافة بينهما إلى 100 قسم متساو كل قسم يعادل درجة فهرنهيتية واحدة (1°F) .

عند مقارنة هذا المقياس بمقياس سلسيوس كانت درجة انصهار الجليد تقابل 32°ف، ودرجة غليان الماء تقابل 212°ف، وبالتالي عند التحويل من سلسيوس (Tc) إلى فارنهايت (Fc) نستخدم العلاقة التالية:

1- Tc × 9/5 + 32 = Tf

وعند التحويل من فارنهايت إلى سلسيوس نستخدم العلاقة التالية:

2-( Tf – 32 ) × 9/5 = Tc

3 -التدريج المطلق أو الكلفني (Absolute or Kelvin Scale) :

صممه اللورد كيلفن حيث اعتبر درجة الحرارة التي ينعدم عندها الطاقة الداخلية للمادة هي الصفر , وتقابل هذه الدرجة في التدريج السيليزي -273.15° , وبإهمال الكسور فإنه يمكن الحصول على الدرجة الكلفنية (المطلقة) من العلاقة:

T°k= Tc + 273 , T°c = T°k – 273

وبذلك تكون درجة انصهار الجليد تقابل على التدريج الكلفني273°K ودرجة غليان الماء 373° K.

الصفر المطلق: هو درجة الحرارة التي ينعدم عندها ضغط كمية معينة من الغاز عند ثبات حجمها. أو هو درجة الحرارة التي ينعدم عندها حجم كمية معينة من الغاز عند ثبات ضغطها.


العلاقة بمكثفات بوز-آينشتاين

المقالة الرئيسية: مكثف بوز-آينشتاين
Velocity-distribution data of a gas of rubidium atoms at a temperature within a few billionths of a degree above absolute zero. Left: just before the appearance of a Bose–Einstein condensate. Center: just after the appearance of the condensate. Right: after further evaporation, leaving a sample of nearly pure condensate.

A Bose–Einstein condensate (BEC) is a state of matter of a dilute gas of weakly interacting bosons confined in an external potential and cooled to temperatures very near absolute zero. Under such conditions, a large fraction of the bosons occupy the lowest quantum state of the external potential, at which point quantum effects become apparent on a macroscopic scale.[1]

This state of matter was first predicted by Satyendra Nath Bose and Albert Einstein in 1924–25. Bose first sent a paper to Einstein on the quantum statistics of light quanta (now called photons). Einstein was impressed, translated the paper from English to German and submitted it for Bose to the Zeitschrift für Physik, which published it. Einstein then extended Bose's ideas to material particles (or matter) in two other papers.[2]

Seventy years later, in 1995, the first gaseous condensate was produced by Eric Cornell and Carl Wieman at the University of Colorado at Boulder NIST-JILA lab, using a gas of rubidium atoms cooled to 170 nanokelvin (nK)[3] (1.7×10−7 K).[4]

A record cold temperature of 450 ± 80 picokelvin (pK) (4.5×10−10 K) in a BEC of sodium atoms was achieved in 2003 by researchers at the Massachusetts Institute of Technology (MIT).[5] The associated black-body (peak emittance) wavelength of 6,400 kilometers is roughly the radius of Earth.

مقاييس درجات الحرارة المطلقة

Absolute, or thermodynamic, temperature is conventionally measured in kelvin (Celsius-scaled increments)[6] and in the Rankine scale (Fahrenheit-scaled increments) with increasing rarity. Absolute temperature measurement is uniquely determined by a multiplicative constant which specifies the size of the degree, so the ratios of two absolute temperatures, T2/T1, are the same in all scales. The most transparent definition of this standard comes from the Maxwell–Boltzmann distribution. It can also be found in Fermi–Dirac statistics (for particles of half-integer spin) and Bose–Einstein statistics (for particles of integer spin). All of these define the relative numbers of particles in a system as decreasing exponential functions of energy (at the particle level) over kT, with k representing the Boltzmann constant and T representing the temperature observed at the macroscopic level.[بحاجة لمصدر]

درجات الحرارة السالبة

المقالة الرئيسية: درجة حرارة سالبة

الصفر المطلق درجة الحرارة النظرية التي تكتسب فيها ذرات المادة وجزيئاتها أقلّ قدرٍ ممكن من الطاقة. تساوي هذه الحرارة، التي يعتقد العلماء أنها الحد الأدنى الممكن بلوغه (- 273,15°م). وقد أُسست هذه القيمة جزئيًا على ملاحظات العلاقة بين الحرارة وضغط الغاز. حين تنخفض درجة حرارة الغاز المعبّأ في جسم ما، فإن ضغطه ينخفض في تناسب طردي بحيث يساوي صفرًا عند - 273,15°م.

ويسمىّ مقياس درجة الحرارة ذو الصفر المطلق في نقطة الصفر، مقياس الحرارة المطلق، ومن أمثلته مقياس كلفن، وهو المعيار العالمي للقياس العلمي للحرارة. يساوي الصفر المطلق في مقياس كلفن صفر كلفن، (صفر ك). ولا تستعمل كلمة درجة ورمز الدرجة (°) في قراءات حرارة كلڤن.

ينتمي مقياس كلفن إلى المقياس سلسيوس (المئوي). ويمكن الحصول على درجة الحرارة بالكلفن بإضافة 273,15° إلى الدرجة المئوية المقابلة فدرجة الحرارة 20°م، على سبيل المثال، تساوي 293,15ك.

ويقول علماء الطبيعة إنّ من المستحيل تحصيل درجة حرارة للصفر المطلق تمامًا. وأدنى درجة حرارة سجّلت حتى الآن هي نحو 0,00001ك، وكان قد تمّ الحصول عليها بتبريد بعض أنواع السبائك. تم مغنطة نوى تلك الفلزات في درجة حرارة منخفضة للغاية في مجال مغنطيسي. وحين أزيح المجال المغنطيسي، أصبحت النوى عديمة الخصائص المغنطيسية، وهبطت درجة حرارتها إلى ما يقرب من الصفر المطلق.

Temperatures that are expressed as negative numbers on the familiar Celsius or Fahrenheit scales are simply colder than the zero points of those scales. Certain systems can achieve truly negative temperatures; that is, their thermodynamic temperature (expressed in kelvins) can be of a negative quantity. A system with a truly negative temperature is not colder than absolute zero. Rather, a system with a negative temperature is hotter than any system with a positive temperature, in the sense that if a negative-temperature system and a positive-temperature system come in contact, heat flows from the negative to the positive-temperature system.[7]

Most familiar systems cannot achieve negative temperatures because adding energy always increases their entropy. However, some systems have a maximum amount of energy that they can hold, and as they approach that maximum energy their entropy actually begins to decrease. Because temperature is defined by the relationship between energy and entropy, such a system's temperature becomes negative, even though energy is being added.[7] As a result, the Boltzmann factor for states of systems at negative temperature increases rather than decreases with increasing state energy. Therefore, no complete system, i.e. including the electromagnetic modes, can have negative temperatures, since there is no highest energy state,[بحاجة لمصدر] so that the sum of the probabilities of the states would diverge for negative temperatures. However, for quasi-equilibrium systems (e.g. spins out of equilibrium with the electromagnetic field) this argument does not apply, and negative effective temperatures are attainable.

وفي 3 يناير 2013، أعلن فيزيائيون أنهم لأول مرة تمكنوا من خلق غاز كمي مصنوع من ذرات پوتاسيوم بدرجة حرارة سالبة في درجات حرية حركة.[8]

التاريخ

Robert Boyle pioneered the idea of an absolute zero.

One of the first to discuss the possibility of an absolute minimal temperature was Robert Boyle. His 1665 New Experiments and Observations touching Cold, articulated the dispute known as the primum frigidum.[9] The concept was well known among naturalists of the time. Some contended an absolute minimum temperature occurred within earth (as one of the four classical elements), others within water, others air, and some more recently within nitre. But all of them seemed to agree that, "There is some body or other that is of its own nature supremely cold and by participation of which all other bodies obtain that quality."[10]

حد لـ"درجة البرودة"

The question of whether there is a limit to the degree of coldness possible, and, if so, where the zero must be placed, was first addressed by the French physicist Guillaume Amontons in 1703, in connection with his improvements in the air thermometer. His instrument indicated temperatures by the height at which a certain mass of air sustained a column of mercury—the pressure, or "spring" of the air varying with temperature. Amontons therefore argued that the zero of his thermometer would be that temperature at which the spring of the air was reduced to nothing.[11] He used a scale that marked the boiling point of water at +73 and the melting point of ice at +51+1⁄2, so that the zero was equivalent to about −240 on the Celsius scale.[12] Amontons held that the absolute zero cannot be reached, so never attempted to compute it explicitly.[13] The value of −240 °C, or "431 divisions [in Fahrenheit's thermometer] below the cold of freezing water"[14] was published by George Martine in 1740.

This close approximation to the modern value of −273.15 °C[6] for the zero of the air thermometer was further improved upon in 1779 by Johann Heinrich Lambert, who observed that −270 °C (−454.00 °F; 3.15 K) might be regarded as absolute cold.[15]

Values of this order for the absolute zero were not, however, universally accepted about this period. Pierre-Simon Laplace and Antoine Lavoisier, in their 1780 treatise on heat, arrived at values ranging from 1,500 to 3,000 below the freezing point of water, and thought that in any case it must be at least 600 below. John Dalton in his Chemical Philosophy gave ten calculations of this value, and finally adopted −3,000 °C as the natural zero of temperature.

قانون تشارلز

From 1787 to 1802, it was determined by Jacques Charles (unpublished), John Dalton,[16] and Joseph Louis Gay-Lussac[17] that, at constant pressure, ideal gases expanded or contracted their volume linearly (Charles's law) by about 1/273 parts per degree Celsius of temperature's change up or down, between 0° and 100° C. This suggested that the volume of a gas cooled at about −273 °C would reach zero.

عمل اللورد كلڤن

After James Prescott Joule had determined the mechanical equivalent of heat, Lord Kelvin approached the question from an entirely different point of view, and in 1848 devised a scale of absolute temperature that was independent of the properties of any particular substance and was based on Carnot's theory of the Motive Power of Heat and data published by Henri Victor Regnault.[18] It followed from the principles on which this scale was constructed that its zero was placed at −273 °C, at almost precisely the same point as the zero of the air thermometer,[12] where the air volume would reach "nothing". This value was not immediately accepted; values ranging from −271.1 °C (−455.98 °F) to −274.5 °C (−462.10 °F), derived from laboratory measurements and observations of astronomical refraction, remained in use in the early 20th century.[19]


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السباق إلى الصفر المطلق

انظر أيضاً: خط زمني لتكنولوجيا درجات الحرارة المنخفضة
لوح تذكاري في لايدن

With a better theoretical understanding of absolute zero, scientists were eager to reach this temperature in the lab.[20] By 1845, Michael Faraday had managed to liquefy most gases then known to exist, and reached a new record for lowest temperatures by reaching −130 °C (−202 °F; 143 K). Faraday believed that certain gases, such as oxygen, nitrogen, and hydrogen, were permanent gases and could not be liquefied.[21] Decades later, in 1873 Dutch theoretical scientist Johannes Diderik van der Waals demonstrated that these gases could be liquefied, but only under conditions of very high pressure and very low temperatures. In 1877, Louis Paul Cailletet in France and Raoul Pictet in Switzerland succeeded in producing the first droplets of liquid air at −195 °C (−319.0 °F; 78.1 K). This was followed in 1883 by the production of liquid oxygen −218 °C (−360.4 °F; 55.1 K) by the Polish professors Zygmunt Wróblewski and Karol Olszewski.

Scottish chemist and physicist James Dewar and Dutch physicist Heike Kamerlingh Onnes took on the challenge to liquefy the remaining gases, hydrogen and helium. In 1898, after 20 years of effort, Dewar was the first to liquefy hydrogen, reaching a new low-temperature record of −252 °C (−421.6 °F; 21.1 K). However, Kamerlingh Onnes, his rival, was the first to liquefy helium, in 1908, using several precooling stages and the Hampson–Linde cycle. He lowered the temperature to the boiling point of helium −269 °C (−452.20 °F; 4.15 K). By reducing the pressure of the liquid helium, he achieved an even lower temperature, near 1.5 K. These were the coldest temperatures achieved on Earth at the time and his achievement earned him the Nobel Prize in 1913.[22] Kamerlingh Onnes would continue to study the properties of materials at temperatures near absolute zero, describing superconductivity and superfluids for the first time.

درجات الحرارة شديدة الانخفاض

The rapid expansion of gases leaving the Boomerang Nebula, a bi-polar, filamentary, likely proto-planetary nebula in Centaurus, has a temperature of 1 K, the lowest observed outside of a laboratory.

The average temperature of the universe today is approximately 2.73 kelvins (−454.76 °F), or about −270.42 °C, based on measurements of cosmic microwave background radiation.[23][24] Standard models of the future expansion of the universe predict that the average temperature of the universe is decreasing over time.[25] This temperature is calculated as the mean density of energy in space; it should not be confused with the mean electron temperature (total energy divided by particle count) which has increased over time.[26]

Absolute zero cannot be achieved, although it is possible to reach temperatures close to it through the use of evaporative cooling, cryocoolers, dilution refrigerators,[27] and nuclear adiabatic demagnetization. The use of laser cooling has produced temperatures of less than a billionth of a kelvin.[28] At very low temperatures in the vicinity of absolute zero, matter exhibits many unusual properties, including superconductivity, superfluidity, and Bose–Einstein condensation. To study such phenomena, scientists have worked to obtain even lower temperatures.

  • In November 2000, nuclear spin temperatures below 100 pK were reported for an experiment at the Helsinki University of Technology's Low Temperature Lab in Espoo, Finland. However, this was the temperature of one particular degree of freedom—a quantum property called nuclear spin—not the overall average thermodynamic temperature for all possible degrees in freedom.[29][30]
  • In February 2003, the Boomerang Nebula was observed to have been releasing gases at a speed of 500,000 km/h (310,000 mph) for the last 1,500 years. This has cooled it down to approximately 1 K, as deduced by astronomical observation, which is the lowest natural temperature ever recorded.[31]
  • In November 2003, 90377 Sedna was discovered and is one of the coldest known objects in the Solar System. With an average surface temperature of -400°F (-240°C),[32] due to its extremely far orbit of 903 astronomical units.
  • In May 2005, the European Space Agency proposed research in space to achieve femtokelvin temperatures.[33]
  • In May 2006, the Institute of Quantum Optics at the University of Hannover gave details of technologies and benefits of femtokelvin research in space.[34]
  • In January 2013, physicist Ulrich Schneider of the University of Munich in Germany reported to have achieved temperatures formally below absolute zero ("negative temperature") in gases. The gas is artificially forced out of equilibrium into a high potential energy state, which is, however, cold. When it then emits radiation it approaches the equilibrium, and can continue emitting despite reaching formal absolute zero; thus, the temperature is formally negative.[35]
  • In September 2014, scientists in the CUORE collaboration at the Laboratori Nazionali del Gran Sasso in Italy cooled a copper vessel with a volume of one cubic meter to 0.006 kelvins (−273.144 °C; −459.659 °F) for 15 days, setting a record for the lowest temperature in the known universe over such a large contiguous volume.[36]
  • In June 2015, experimental physicists at MIT cooled molecules in a gas of sodium potassium to a temperature of 500 nanokelvin, and it is expected to exhibit an exotic state of matter by cooling these molecules somewhat further.[37]
  • In 2017, Cold Atom Laboratory (CAL), an experimental instrument was developed for launch to the International Space Station (ISS) in 2018.[38] The instrument has created extremely cold conditions in the microgravity environment of the ISS leading to the formation of Bose–Einstein condensates. In this space-based laboratory, temperatures as low as 1 picokelvin (10−12 K) are projected to be achievable, and it could further the exploration of unknown quantum mechanical phenomena and test some of the most fundamental laws of physics.[39][40]
  • The current world record for effective temperatures was set in 2021 at 38 picokelvin (pK), or 0.000000000038 of a kelvin, through matter-wave lensing of rubidium Bose–Einstein condensates.[41]

انظر أيضاً

المراجع

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