Towards the Unification of Gravity and other Interactions: What has been Missed?

Faced with the persisting problem of the unification of gravity with other fundamental interactions we investigate the possibility of a new paradigm, according to which the basic space of physics is a multidimensional space ${\cal C}$ associated with matter configurations. We consider general relativity in ${\cal C}$. In spacetime, which is a 4-dimensional subspace of ${\cal C}$, we have not only the 4-dimensional gravity, but also other interactions, just as in Kaluza-Klein theories. We then consider a finite dimensional description of extended objects in terms of the center of mass, area, and volume degrees of freedom, which altogether form a 16-dimensional manifold whose tangent space at any point is Clifford algebra Cl(1,3). The latter algebra is very promising for the unification, and it provides description of fermions.Comment: 11 pages; Talk presented at "First Mediterranean Conference on Classical and Quantum Gravity", Kolymbari, Crete, Greece, 14-18 September 200

Spin Gauge Theory of Gravity in Clifford Space: A Realization of Kaluza-Klein Theory in 4-Dimensional Spacetime

A theory in which 4-dimensional spacetime is generalized to a larger space, namely a 16-dimensional Clifford space (C-space) is investigated. Curved Clifford space can provide a realization of Kaluza-Klein theory. A covariant Dirac equation in curved C-space is explored. The generalized Dirac field is assumed to be a polyvector-valued object (a Clifford number) which can be written as a superposition of four independent spinors, each spanning a different left ideal of Clifford algebra. The general transformations of a polyvector can act from the left and/or from the right, and form a large gauge group which may contain the group U(1)xSU(2)xSU(3) of the standard model. The generalized spin connection in C-space has the properties of Yang-Mills gauge fields. It contains the ordinary spin connection related to gravity (with torsion), and extra parts describing additional interactions, including those described by the antisymmetric Kalb-Ramond fields.Comment: 57 pages; References added, section 2 rewritten and expande

Spin Gauge Theory of Gravity in Clifford Space

A theory in which 16-dimensional curved Clifford space (C-space) provides a realization of Kaluza-Klein theory is investigated. No extra dimensions of spacetime are needed: "extra dimensions" are in C-space. We explore the spin gauge theory in C-space and show that the generalized spin connection contains the usual 4-dimensional gravity and Yang-Mills fields of the U(1)xSU(2)xSU(3) gauge group. The representation space for the latter group is provided by 16-component generalized spinors composed of four usual 4-component spinors, defined geometrically as the members of four independent minimal left ideals of Clifford algebra.Comment: 9 pages, talk presented at the QG05 conference, 12-16 September 2005, Cala Gonone, Ital

A Novel View on the Physical Origin of E8

We consider a straightforward extension of the 4-dimensional spacetime $M_4$ to the space of extended events associated with strings/branes, corresponding to points, lines, areas, 3-volumes, and 4-volumes in $M_4$. All those objects can be elegantly represented by the Clifford numbers $X\equiv x^A \gamma_A \equiv x^{a_1 ...a_r} \gamma_{a_1 ...a_r}, r=0,1,2,3,4$. This leads to the concept of the so-called Clifford space ${\cal C}$, a 16-dimensional manifold whose tangent space at every point is the Clifford algebra ${\cal C \ell }(1,3)$. The latter space besides an algebra is also a vector space whose elements can be rotated into each other in two ways: (i) either by the action of the rotation matrices of SO(8,8) on the components $x^A$ or (ii) by the left and right action of the Clifford numbers $R=$exp [\alpha^A \gam_A] and $S=$exp [\beta^A \gam_A] on $X$. In the latter case, one does not recover all possible rotations of the group SO(8,8). This discrepancy between the transformations (i) and (ii) suggests that one should replace the tangent space ${\cal C \ell}(1,3)$ with a vector space $V_{8,8}$ whose basis elements are generators of the Clifford algebra ${\cal C \ell}(8,8)$, which contains the Lie algebra of the exceptional group E$_8$ as a subspace. E$_8$ thus arises from the fact that, just as in the spacetime $M_4$ there are $r$-volumes generated by the tangent vectors of the spacetime, there are $R$-volumes, $R=0,1,2,3,...,16$, in the Clifford space ${\cal C}$, generated by the tangent vectors of ${\cal C}$.Comment: 14 page

The effects of socio-political context on tourism

Purpose: The purpose of this paper is to examine the effects of tourists’ perceptions of political and economic instability and risks of terrorism on their intentions to travel to countries associated with various risks. Design/methodology/approach: A total of 648 Greek, Israeli and Portuguese students completed a questionnaire focusing on their perceptions concerning factors that shape their travel decisions. Findings: The findings showed that among tourists from Greece and Portugal, the experience of economic crisis and the salience of economic and political hardships mitigated their intentions to travel to destinations with similar problems. These factors had no effect on Israelis, who have not experienced such problems in their country. Frequent terrorist incidents diminished the intentions of Greek tourists to travel to destinations marked by terrorism, such as Israel. Thus, different factors affect tourists’ travel-related decisions in each of the three countries. Originality/value: The study sheds light on how potential tourists construe the risks of traveling to specific destination countries based on hazards in their home countries, a topic that to date has received little research attention.info:eu-repo/semantics/acceptedVersio

Factors shaping young tourists' intentions to travel to Greece, Israel and Portugal: Universal or idisyncratic perceptions of young Greeks, Israelis and Portugese?

Tourism constitutes an important branch of economy, especially in countries experiencing economic crisis and harsh socio-political events. The current study compares the intention of young people from three different countries – Greece, Israel and Portugal - to travel to two selected destinations. For each country of origin the other two countries were the destination of interest. This research examined the factors affecting young tourists' intention to travel to different destinations assuming that those determinants depend on the country of origin as well as on the destination country. The sample comprised of 648 students: Israelis (277), Portuguese (200), Greeks (171). The research questionnaire was distributed in Israeli, Greek and Portuguese academic institutions in 2014. The results indicate that over half of the Israelis intend to visit Greece or Portugal. The majority of the Portuguese anticipate visiting Greece, while only 32.5% expect to visit Israel. Among the Greeks nearly 50% intend to visit Portugal and do not intend to visit Israel. The study showed that the main factors affecting the decisions of young Portuguese to travel to Israel were: the image of Israel, the perceived risk of traveling to a country with political unrest and the number of trips abroad. The main factors affecting the decisions of young Greeks were the perceived risk of traveling to a country with political unrest and Israel's image. Israelis' decision to travel to Greece was affected by their image of Greece; the Portuguese also took into account the perceived risk regarding economic situation. For Israelis, considering Portugal as a traveling destination was related to the destination's image. The Greeks were affected by the number of Facebook friends and the Innovation, Entrepreneurship and Digital Ecosystems perceived economic risk. This research suggests that the socio-economic, political context of the country of origin and of the tourist destination plays an important role in young tourists' travelling-related decision-making.info:eu-repo/semantics/publishedVersio

Analyzing the effect of socio-political context on tourism: perceptions of young tourists in Greece, Portugal and Israel

International crises that affect tourism, such as terror attacks, political unrest, and economic crises have become more frequent, and their influence has become broader. The influence of such extreme events depends on their salience in the tourists' awareness. Hence, it is important to understand the mechanisms underlying tourists' selection of travel destinations, especially their perceptions of crisis-related events and the impact of the sociopolitical and economic context in their countries of origin. The current study examined how the socio-political and economic context in the home countries of potential young tourists affected their selection of travel destinations. The objective was to elucidate how the salience of various crises (economic and political) in the tourists' perceptions, due to their experiences at home, color their construal of destinations affected by similar hazards and influence their travel intentions. The study focused on student tourists from Israel, Greece, and Portugal. Today about a fifth of international tourism is based on young people, especially students. These countries were chosen since Greece and Portugal are in the midst of economic crises. In addition, Greece and Portugal have experienced political instability, while Israel has security-related problems (including terrorist incidents). In 2013, a total of 648 students, responded to a questionnaire that included questions concerning attitudes and risk perceptions regarding travel to destinations with various risk hazards as well as socio-demographic details. The results indicate that over half of the Israelis intend to visit Greece or Portugal. The majority of the Portuguese intend to visit Greece, while less than a third of them intend to visit Israel. About half of the Greeks intend to visit Portugal, and most of them do not intend to visit Israel. The results indicate that greater perceived importance of economic crises mitigates the intention to travel to destinations with economic crises for tourists from origin countries that are also marked by economic crises, such as Greece and Portugal. However, for tourists from Israel, a country with a relatively stable economy, issues related to the economy barely affect their intention to travel to the other two countries. The findings also suggest that Greeks and Portuguese who are highly concerned about political unrest are unlikely to select Israel as a tourist destination. In addition, strong apprehension regarding terrorism impedes the intention to travel to destinations marked by terrorist incidents, such as Israel. The current research contributes to the existing literature by highlighting the impact of travelers' personal previous experience with crisis on their risk perceptions and in turn on their intentions to travel to countries with similar risks. Therefore, in a world where such incidents are on the rise, understanding tourists' risk perceptions and behavior and the factors influencing their destination-related decisions are crucial for countries that wish to increase the numbers of incoming tourists.info:eu-repo/semantics/publishedVersio

Mooney et al. Respond to "observing Neighborhood Physical Disorder"

[No abstract available

Street Audits to Measure Neighborhood Disorder: Virtual or In-Person?

Neighborhood conditions may influence a broad range of health indicators, including obesity, injury, and psychopathology. In particular, neighborhood physical disorder - a measure of urban deterioration - is thought to encourage crime and high-risk behaviors, leading to poor mental and physical health. In studies to assess neighborhood physical disorder, investigators typically rely on time-consuming and expensive in-person systematic neighborhood audits. We compared 2 audit-based measures of neighborhood physical disorder in the city of Detroit, Michigan: One used Google Street View imagery from 2009 and the other used an in-person survey conducted in 2008. Each measure used spatial interpolation to estimate disorder at unobserved locations. In total, the virtual audit required approximately 3% of the time required by the in-person audit. However, the final physical disorder measures were significantly positively correlated at census block centroids (r = 0.52), identified the same regions as highly disordered, and displayed comparable leave-one-out cross-validation accuracy. The measures resulted in very similar convergent validity characteristics (correlation coefficients within 0.03 of each other). The virtual audit-based physical disorder measure could substitute for the in-person one with little to no loss of precision. Virtual audits appear to be a viable and much less expensive alternative to in-person audits for assessing neighborhood conditions